GEOTHERMAL ENERGY ll R&D PROGRAM

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GEOTHERMAL ENERGY R&D PROGRAM

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ANNUAL PROGRESS REPORT FOR

FISCAL YEAR 1993

APRIL, 1994

prepared for:

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GEOTHERMAL DMSION U.S. Department of Energy

prepared by:

Princeton Economic Research, Incorporated 1700 Rockville Pike, Suite 550

Rockville, MD 20852

Under Contract No. DEAC01-93CE35060

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

DISCLAIMER

"This report was prepared as an account of work sponsored by an agency of the United States Government. Nzither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute nor imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof."

This report has been reproduced directly from the best available copy.

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TABLE OF CONTENTS

EXECUTIVESUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

PROGRAM MANAGEMENT AND BUDGET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

EXPLORATION TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 GEOPHYSICAL METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Enhanced Self Potential Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Heat Flow Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

GEOCHEMICALMETHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 LONGVALLEYEXPLORATORYWELL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

DRILLINGTECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 LOST CIRCULATION CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 MEMORYLOGGINGTOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 ADVANCED SYNTHETIC-DIAMOND DRILL BITS . . . . . . . . . . . . . . . . . . . . . 37 ACOUSTIC DATA TELEMETRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 SLIMHOLE DRILLING FOR GEOTHERMAL EXPLORATION . . . . . . . . . . . . . . 43 GEOTHERMAL DRILLING ORGANIZATION . . . . . . . . . . . . . . . . . . . . . . . . . 46

RESERVOIR TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 RESERVOIR ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Reservoir Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Improved Dual-Porosity Models for Simulating the Behavior of Fractured

Geothermal Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Flow Visualization and Relative Permeability Measurements in Rough-Walled

Fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Conceptual and Numerical Models of Geothermal Reservoirs . . . . . . . . . . . . 53 International Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Characterization of Fracture and Vein-Controlled Porosity and Permeability in

Active Geothermal Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Thermodynamics and Phase Relations in Granite Melts . . . . . . . . . . . . . . . . 57 Experimental and Theoretical Investigation of the Production of HCl and Some

Metal Chlorides in MagmaWHydrothermal Systems . . . . . . . . . . . . . 58 BRINE INJECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Well Test and Tracer Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Water Injection into Vapor Dominated Geothermal Reservoirs . . . . . . . . . . . . 61 Tracer Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

BRINECHEMISTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Liquid Vapor Distribution of HCl (as> . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Aluminum Speciation and Hydroxide Solubility . . . . . . . . . . . . . . . . . . . . . 66 L-V Distribution of Isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Geochemical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

HOTDRYROCKRESEARCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 GEYSERS COOPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Reservoir Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Adsorption and Tracer Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Corrosion Mitigation at The Geysers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

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Microearthquake Monitoring at The Geysers . . . . . . . . . . . . . . . . . . . . . . 84

86 Gas and Isotope Geochemistry of Geysers Steam . . . . . . . . . . . . . . . . . . . . 85 Lake County Effluent Pipeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Geysers Steamfield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Geysers Geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Geology and MagmatidHydrothermal History of the Hypabyssal Felsite Beneath

Vapor-Phase Tracer Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 GEOTHERMAL TECHNOLOGY ORGANIZATION . . . . . . . . . . . . . . . . . . . . . . 95

CONVERSION TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 HEATCYCLERESEARCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 ADVANCED HEAT REJECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 ELASTOMER BONDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 THERMALLY CONDUCTIVE POLYMER CONCRETES . . . . . . . . . . . . . . . . . . 110 FIELD TESTING OF THERMALLY CONDUCTIVE POLYMER CONCRETE . . . . 113 WELLCEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 LOST CIRCULATION CONTROL MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . 118 ADVANCED BIOCHEMICAL PROCESSES FOR GEOTHERMAL BRINES . . . . . . 121 BOISECI TY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 LOW-TEMPERATURE RESOURCE ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . 126 LOW-TEMPERATURE APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

Cascaded Direct-Use Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 GEOTHERMAL HEAT PUMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

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D EXECUTIVE SUMMARY

Overview u

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Research in Geothermal Energy has been conducted, on a national scale, since 1971 under the supervision and funding of the Department of Energy (DOE) and its predecessors. To develop the technology needed to harness the nation’s vast geothermal resources, DOE’S’ Geothermal Division oversees a network of national laboratories, industrial contractors, universities, and their subcontractors. The following mission and vision statements guide the overall activities of the Geothermal Division.

Mission

In partnership with industry and other stakeholders, plan and manage a balanced program of research, development, and demonstration that wi l l stimulate an expanding use of geothennul energy for environmentally sound electric power genemtion and direct use applications.

Vision

Achieve furr competitive status for the geothennul industry in domestic markets.

Mainlain leadership for U.S. geothennul industry in world markets.

Gain recognition of geothermal as an abundant, reliable, economic, and environmentally beneficid energy resource.

This Annual Progress Report reviews the specific objectives, status, and accomplishments of DOE’s geothermal R&D program. The information contained in this Annual Progress Report illustrates how the mission and vision of the Geothermal Division is reflected in each R&D activity. The geothermal R&D program, from its guiding principles to the most detailed research activities, is focused on expanding the use of geothermal energy.

Research Focus

In accordance with the mission and vision, the R&D program is currently designed to serve two broad purposes: 1) to assist industry in overcoming near-term barriers by conducting cost-shared research that allows geothermal energy to- compete in today’s aggressive energy markets; and 2) to undertake fundamental (or core) research with potentially large commercial payoffs.

Since the inception of the Geothermal Program, the Federal Government and private industry have worked closely together - in promising new research directions, as well as in overcoming difficult technical barriers -- to establish an extensive geothermal knowledge base. Over the-past two decades industry, in turn, has succeeded in creating an infrastructure that translates research results into marketplace applications. The DOEhndustry partnership guides the DOE research program towards more cost-competitive power generation from geothermal resources. This partnership assesses the value of long-term research options as well. Private-sector inputs to DOE’s planning process are critical to a logical, balanced strategy for the geothermal research program. This joint strategy serves to increase geothermal energy’s role in the U.S. electric utility sector.

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The Work Breakdown Structure (WBS) for FY93 (see Figure 1) reflects DOE’S commitment to both continuing research (identified as Core Research) and short-term, cooperative research with industry (identified as Industrial Development). This research is organized by the four components of a geothermal project (see Figure 2).

INDUSTRIAL DEVELOPMENT

I CATEGORY I TASK I PROJECT

DRILLING APPLICATIONS

RESERVOIR ENGINEERING APPLICATIONS

DIRECT HEAT APPLICATIONS

CORE RESEARCH

EXPLORATION TECHNOLOGY Geophysical Methods Geochemical Methods

DRILLING TECHNOLOGY

RESERVOIR TECHNOLOGY

Lost Circulation Control Instrumentation Acoustic Data Telemetry

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Reservoir Analysis Brine Injection Brine Chemistry

CONVERSION TECHNOLOGY Heat Cycle Research Heat Rejection Systems Materials Development Waste Disposal

INDUSTRY-COUPLED DRILLING

Basin and Range Exploration Long Valley Exploration

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Slimhole Drilling Systems Geothermal Drilling Organization

Geysers Cooperation Geothermal Technology Organization

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Boise City Low Temperature Resource Assessment Low Temperature Applications Heat Pump Technology Transfer

ngure 1. Geothermal Program Work Breakdown Structure

EXPLORATION TECHNOLOGY: Most of the hydrothermal systems with obvious surface manifestations have been explored. New hydrothermal discoveries will require exploration in frontier areas where the reservoirs are either concealed or lie at greater depths. The Exploration Technology task focuses on developing instruments and techniques to discover hidden hydrothermal systems and to explore the deep portions of known systems.

Research in geophysical and geochemical methods is expected to yield increased knowledge of hidden geothermal systems. Improved exploration techniques and data interpretation methods will facilitate expanding the geothermal resource base. Cost-shared exploration to discover new geothermal fields in the Basin and Range Province. Deep drilling at Long Valley offers new insights into the nature of young silicic volcanic centers and also serves as a testing ground for new drilling and logging equipment.

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Figure 2. Schematic Diagram of a Geothermal System and its Component Technologies.

DRILLING TEcmoUx;~: Drilling and completion of wells for exploration, production, and injection account for 35 to 50 percent of the cost of generating electricity from geothermal resources. Current geothermal drilling and completion technology derives primarily from the oil and gas industry. This technology is often unsuitable for the high temperatures, hard rock, and highly corrosive fluids found in the hostile geothermal environment. The Drilling Technology task focuses on developing improved, economic drilling and completion technologies for geothermal wells.

Ongoing research to avert lost circulation episodes in geothermal drilling is yielding positive results. Field testing of two prototype packer elements is underway to confine and regulate cementing operations in geothermal wells. Flow meters capable of measuring flow rates into and out of a well are also being field tested. The borehole televiewer for fracture characterization has reached the commercialization stage. Advanced drilling bits are under development. Slimhole drilling, which reduces exploration drilling costs by as much as 50 percent, will facilitate reservoir confirmation. Cost-shared investigations to develop the acoustic telemetry system for measurement-whiledrilling is also underway.

RESERVOIR TECHNOLOGY: The geothermal industry has made progress in devising techniques for characterizing and developing hydrothermal reservoirs. Nevertheless, reservoir technology still suffers from several major uncertainties, such as those encountered in assessing reservoir productivity and sustainability, and in assessing the extent of field reserves. These uncertainties may lead to overproduction in a field and premature pressure and production declines. The Reservoir Technology task combines laboratory and analytical investigations with equipment development and field testing to establish practical tools for resource development and management for both hydrothermal and hot dry rock reservoirs.

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Research in various reservoir analysis techniques is generating a wide range of information that facilitates development of improved reservoir management tools. Improved tracer data interpretation techniques will optimize injection strategies and increase resource longevity. Capabilities for predicting scaling and corrosion caused by different chemical reactions have improved markedly with the ongoing research in brine chemistry. Long-term flow testing at the Fenton Hill hot dry rock site has enabled data gathering that will facilitate commercialization of the technology. Efforts are also underway to minimize reservoir pressure depletion at The Geysers and extend the resource lifetime.

CONVERSION TECHNOLOGY: The three conversion technologies in use for electricity generation are: 1) Dry steam conversion, such as that used at The Geysers in California since 1960; 2) Flash steam plants, favored for liquiddominated or two-phase resources when the resource temperature is over 150°C (360°F); and 3) Binary cycles, favored for low to moderate resource temperatures in the range of 100" to 150°C. Dry steam and flash steam plants are mature technologies generating cost competitive electricity. Binary-cycle power plant technology is less mature, only recently coming into general use as an economic conversion alternative. The Conversion Technology task focuses on reducing costs and improving binary conversion cycle efticiency to permit greater use of the more abundant moderate- temperature geothermal resource.

Increased output and improved performance of binary cycles will result from investigations in heat cycle research. High-temperature, scale- and corrosion-resistant, and thermally-conductive liner materials are under development for heat exchanger applications and energy conversion processes. C0,-resistant well cements which are able to withstand the aggressive chemistry of geothermal fluids are also under development. Biotechnology solutions for geothermal waste disposal problems are being investigated. An assessment of low-temperature resources will facilitate increased use of these abundant resources for district heating and heat pump applications.

Major R&D Accomplishments for FY93 =Data was compiled and a U.S. map was published for heat flow, rock type, and conductivity to

basement. This new compilation is at a spatial resolution of about 5 minutes (about 3 to 5 km) and will allow estimation of temperatures at depth, particularly in the eastern and central United States, with much greater precision than in the past. The heat flow map will help to identify geothermal prospects.

fp A detailed model of the Cos0 geothermal system was developed. Comparison of the fluid inclusions in rocks and measured temperatures indicates that cooling has occurred along the top and margins of the geothermal system while temperatures have continued to increase within the core of the field. The model will serve as a reservoir management tool that will assist in identifying production and injection well sites, zones of aggressive brine chemistry, and changes in reservoir-related parameters.

fp A new method was developed for simulating fluid flow in fractured geothermal reservoirs. The method is more accurate than the current model used by industry and has been incorporated into a computer module compatible with the MULKOM/TOUGH family of reservoir simulators. Since the flow in geothermal reservoirs is mostly fracture-based rather than porosity-based, this model will allow better predictions of reservoir capacity and longevity.

Numerical techniques were developed for the simultaneous interpretation of pressure transient and tracer tests. This will allow tracking of fluid flow paths and serve as a reservoir management tool.

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ciu Numerical modeling studies of injection of liquid water into vapordominated geothermal reservoirs confirmed the existence of a very efficient heat transfer process in vapor zones due to the development of heat pipes (water and vapor counterflow) and that the water saturation near the injection point will increase. These studies also showed that: 1) in relatively high-permeability systems, single-phase liquid zones prevail, with convection providing the energy throughput; 2) in lower permeability systems a two-phase liquiddominated zone develops; and 3) for regions with high heat flow, a high- temperature single-phase vapor zone can develop below a typical vapordominated zone. Understanding the heat transfer process is key to maintaining optimum energy production from geothermal reservoirs.

A more accurate equation of state was developed for the NH,-H,O binary system. The equation, which predicts thermodynamic properties within experimental accuracy, has been incorporated into the GEOFLUID brine chemistry model. This will enhance GEOFLUID’s capabilities in exploration and power system design.

A model was developed to predict the origin of distinct (but connected) reservoirs in the northwest and southeast Geysers based on differences in depth, access to recharge water, and rock types. This model will assist in identifying future production and injection strategies, and in increasing the reservoir iife- time.

GP Three wells were successfully logged using newly developed borehole televiewer data acquisition and display software. Further, UNOCAL began commercial operation of the high-temperature borehole acoustic televiewer in Indonesia. The televiewer, developed at Sandia National Laboratories with government funding, is used to measure the thickness of fractures associated with lost circulation and fracture zones. Its use facilitates detecting better flow zones increasing the flow rate of production wells and the net output per well.

e A-Z Grantfinternational, a member of the Geothermal Drilling Organization, completed an improved stripper rubber design for geothermal wells in a cost-shared effort with the Government. The stripper rubber design will contribute to improved geothermal drilling practices.

Limited long-term testing was completed at the Fenton Hill hot dry rock test facility. This concludes eight months of flow operations including two long, steady-state flow segments of 112 days and 65 days, respectively. It was verified that no atmospheric emissions resulted from operation of the facility under the standard closed-loop operating conditions. These test results will assist in gaining confidence to commercialize hot dry rock electricity systems. - All component development and testing was completed for the drillable straddle packer, including the shroud mechanism, drillstring coupler, and two bag designs for reliably sealing 20 psi with an appropriate safety factor. Conceptual design of the Packer Demonstration Facility was also completed. Packers are important tools in geotherma well-cementing operations, preventing mud from plugging production zones or directing mud to plug lost circulation zones.

ciu Heat transfer calculations were completed and cost evaluations of thermally-conductive polymer concrete linings were performed that confirmed the potential cost effectiveness of the material. Polymer concretes are corrosion resistant and, therefore, enable power production from reservoirs with aggressive chemical characteristics.

Researchers observed the behavior of metastable expansions of hydrocarbon working fluids in binary cycles. If such expansions can be realized in commercial binary-units, higher thermodynamic efficiencies and lower costs can be achieved.

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PROGRAM MANAGEMENT AND BUDGET

a PROGRAM MANAGEMENT AND BUDGET

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As Figure 3 depicts, the Geothermal Division operates under the administrative oversight of the Office of Renewable Energy Conversion under the Office of the Deputy Assistant Secretary for Utility Technologies. With the oversight of these offices, the Geothermal Division is responsible for overall program management, implementing energy policy at the program level, and allocating technical and budgetary resources for program activities. In addition, the Division works in cooperation with other offices within the Department of Energy (e.g., the Office of Energy Research, and the Office of Technical and Financial Assistance) on activities of mutual interest.

The Geothermal Division’s research and development program is conducted with the participation of national laboratories, universities, and industrial contractors. The Albuquerque and Idaho Operations Offices and the Golden Field Office are responsible for implementing program plans, executing prime contracts for research, directing contractors and reviewing their performance, and providing the Geothermal Division with recommendations on program needs and direction. Actual implementation of the geothermal research program and day-today management of the research activities are performed by contractors, including national laboratories, universities, and industry. Industry participation is coordinated through liaison committees organized by the national laboratories.

Office of Renewable Energy Conversion

Geothermal Division

National Laboratories, Universities, Industrial Contractors

Figure 3. Geothermal Research and Development Program Participants.

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Figure 4 presents the management organization of the Geothermal Division. The Division Director implements energy research policy and allocates resources for program activities, The Division Director also provides guidance to field offices and national laboratories, and approves their annual plans in accordance with national energy policy. The Division is organized into two teams, geosciences and energy conversion, with each team having a leader that oversees project activities in accordance with the work breakdown structure. The geosciences team is responsible for tasks including exploration technology, reservoir technology, industry-coupled drilling, and reservoir engineering applications. The remaining tasks, drilling technology, conversion technology, drilling applications, and direct heat applications are the responsibility of the energy conversion team. A staff member of the division is assigned to manage and oversee individual tasks and projects.

Through research, development, demonstration, and commercialization activities, the Geothermal Division’s goal is to foster the use of geothermal energy to take full advantage of the Nation’s geothermal resources. The Division administers research programs through the management-by-objectives approach. n e Division measures progress by matching accomplishments against research objectives set for each major task, project, or activity. Annual peer-review sessions are conducted to evaluate the quality of each research activity, the performance of researchers, and the anticipated benefits of the research. An annual program review meeting is also convened to discuss research results with members of the geothermal community and industry. As part of this annual meeting, industry sessions are conducted to discuss industry needs and cost-shared research topics. Ad-hoc meetings are held, as required, to address any emergent or unplanned issues.

MARSHALL J REED Manager

ExpbraborvResewolr T e c h b g y

GLADYS J HKJPER Manager

Hot Dry RocklBrm Cknnsby

RAYMOND FORTUNA Marager

Geopesswed Program / GeothrmalTest Facilty

LEWW PRATSCH Manager

Drilltrg Technow I Heat Pump

RAYMOND J LASALA Manager

Hear Cycb IMatermk Oevebpnent

STANLEY CALVERT Manager

Direct Use Ap@lcabons

Figure 4. Management Structure of the Geothermal Division

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The table in Figure 5 presents the Geothermal Research and Development Budget for Fiscal Years 1992 through 1995. Management and operations includes staff support and equipment to support programmatic laboratory and field efforts.

CORE RESEARCH Exploration Technology Drilling Technology Reservoir Technology Conversion Technology Environment

INDUSTRIAL DEVELOPMENT Industry-Coupled Drilling Drilling Applications Reservoir Engineering Applications Direct Heat Applications

TOTAL

MANAGEMENT & OPERATIONS Program Direction Capital Equipment

TOTAL

TOTAL GEOTHERMAL R&D

1992

578 2,000 13,600 3,975

--

622 900

2,000 1,325

25,000

1,000 900

1,900

26,900

Actual Est.

1994

2,500 2,200 5,412 6,615 1,000

200 1,200 2,500 325

22,072

1,000 900

1,900

23,972

1995

2,700 4,900 6,800 4,875 10,177

2,000 1,500 2,000 325

35,277

1,000 900

1,900

37,177

Figure 5. Geothermal Research and Development Budget ($1,000~)

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EXPLORATION TECHNOLOGY

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Most of the obvious hydrothemal systems have been explored. New hydrothemal discoveries will require exploration incfiontier areas where the reservoirs are either concealed or at greater depths. The Exploration Technology task develops techniques to locate and characterize hidden geothemal resources. Geophysical and geochemical exploration techniques are validated and improved through cost-shared exploration within the Basin and Range province. The Long Valley deep exploration well is providing valuable infonnation that is used to study the subsurface geology, chemistry, structure, and geothermal potential. The well also serves as a testing ground for new tools and techniques.

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FY93 ANNUAL PROGRESS REPORT EXPLORATION TECHNOLOGY

GEOPHYSICAL METHODS

To expand its resource base, the geothermal industry needs to reduce exploration and field development costs. Exploratory drilling accounts for much of these costs, and can be reduced by making geophysical methods for locating and characterizing reservoirs more accurate. More effective techniques to evaluate reservoir potential serve to reduce geothermal development front-end costs. These costs frequently reflect the developers’ equity investment, and limit the extent and speed of development. A more accurate understanding of the reservoir, in turn, facilitates better plant design. And, finally, lowered exploration costs stimulate exploration on a regional level.

In view of the above, researchers at Southern Methodist University, the University of Utah Research Institute (UURI), and Lawrence Livermore National Laboratory are conducting research to improve existing geophysical methods.

Objectives

b To @Ether develop, improve, and test selected geophysical techniques for exploring geothemal resources and to direct drilling and monitoring production in disconnected reservoirs.

F To reduce geothermal exploration and development costs, mainly associated with drilling, and to minimize the environmental impact in exploring for and producing new resources.

To develop improved data collection and interpretation techniques for the self potential method.

b To produce a heat flow data set in contour and grid form for the U.S. at a resolution of less than 10 km.

Enhanced Self Potentia/ Techniques Background

Improved measurement and interpretation methods, and exploration strategies can reduce the cost of discovering and operating geothermal fields. Researchers at Lawrence Livermore National Laboratory (LLNL) are conducting studies on enhanced self-potential techniques to provide these improvements.

Electrical self-potential (SP) surveys provide the only geophysical method that directly measures the effects of heat and mass transport, which are crucial for the detection and observation of geothermal fields. Most SP surveys are relatively crude, with widely spaced lines and relatively simple interpretation approaches. While this makes SP attractive as a relatively inexpensive exploration tool, researchers believe much more information can be gained by applying advanced data collection and interpretation techniques. Enhanced SP methods can thus be an inexpensive means to acquire more information about the patterns of heat and mass flow within a geothermal system. The information will provide two benefits: 1) in the short run, it allows operators to better understand the changes induced within their fields by production and injection; 2) in the longer run, it provides better tools to locate possible geothermal systems in unexplored districts in the western U.S. These tools will provide new candidates for geothermal production.

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Approach

Phase I Field surveys in various geothermal environments (SP, MT).

Phase I1 Instrumentation and field methodology improvement.

Phase III Algorithm and interpretation development.

Phase IV Reporting and technology transfer.

UUFU researchers will develop improved electrical geophysical techniques that have broad applicability to mapping geothermal resources on both regional and detailed scales. They will continue to test existing methods, improve techniques and equipment for gathering field data, and improve interpretation algorithms and computer programs. Integrated geoscience interpretations will provide additional insight into these methods. At present, research is focused on the magnetotelluric (MT), self-potential (SP), and cross-borehole electrical methods. Improvements in signalhoise ratios, cost-effective data gathering, and numerical and geological interpretations are expected. F The LLNL research approach has two parts: 1) work with the University of Arizona to enhance existing data interpretation codes, including a compilation of all existing laboratory data on cross-coupling coefficients in rocks, and to model more complex 2-D structures; and 2) conduct field experiments to test the value of spatial and areal filtering methods on SP data. By eventually combining the results of these two efforts, an improved exploration and monitoring technology will be developed.

Research Status and Findings

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L figure 6. Grey-scale rendition of finite element model cross section.

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fl93 ANNUAL PROGRESS REPORT EXPLORATION TECHNOLOGY

Researchers completed field surveys over several hidden and exposed geothermal systems in cooperation with industry and state resource t e r n (see Figure 6) including: Carson Lake, Nevada (an Oxbow Power Corporation prospect); Meadow-Hatton Hot Springs and Table Butte area, Utah; Pilgrim Springs, Arkansas; and Tortugas Mountain-Las Cruces East Mesa, New Mexico. They characterized SP anomalies for these resources (see Figure 7), and identified significant geologic noise sources (sand dunes at Carson Lake, Nevada; caliche-capped hills at Tortugas Mountain). Data interpretation is underway. Results of earlier SP studies in Utah during FY91 and FY92 were published and presented at technical meetings.

SP field studies are well underway but quantitative and geologic interpretation lags behind the field effort. Some innovation in field survey techniques, adaptable to regional-scale exploration, is possible. Results to date have led to more requests for detailed SP surveys by state teams and industry.

Magneto iefluric:

Figure 7. Self-potential survey results, Rincon area, New Mexico. SP Contour intervals are 10 and 50 mV.

Researchers continued the upgrade of MT instrumentation and noise-reduction algorithms for the UURI MT system. The field-tested capability of the wideband MT system includes simultaneous, dual-site measurement with each site acquiring five channels of EM field time series (Ex, Ey, Hx, Hy, HJ. Time series are transmitted in digital form via radio telemetry to a recording truck and processed in real time. Operation at truck is cmied out using an IBM compatible PC-80486 and a multi-tasking control program (Quarterdeck’s DeskView (R)) to prioritize individual jobs each running under MS-DOS. Time series processing at the truck is based on cascade decimation, allowing real-time data quality assessment and a virtually finished MT sounding on-site (see Figure 8). The time series are archived together with the MT spectra and impedance functions for further processing. Field tests were conducted to resolve instrument and telemetry problems. Interpretation of a high-quality tensor CSAMT survey at Valles Caldera, New Mexico was completed and compared scalar natural field (MT) results. Development of 2-D and 3-D resistivity structure simulation and inversion algorithms is underway, but tome and costs for complex model interpretations can be further reduced. A major upgrade for the MT field recording system nears completion, minor improvements will be ongoing. Field surveys are needed to define new recording efficiencies and to demonstrate the viability of SP methods for deep electrical explorations in priority geothermal areas.

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FY93 ANNUAL PROGRESS REPORT EXPLORATION T E C ~ O L O G Y

Eastern Great Basin MT Transect

% --\ 0

'm Thrust Fault Normal Fault

thin rhwe Inferred) dashed where MT Site (tb.th On Upper plate, (ball on down rlde, Outcrop

Inferred)

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114.W 113'W

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Figure 8. Location of study area in southern Cordilleran hingeline of Utah and Nevada, and detailed MT site positions.

k Cross-Borehole Electrical Methods:

Researchers completed integration of a first generation cross-borehole field system which consists o f

1. A small logging truck with a winch containing 3,500 feet of logging cable rated to 250°C (the receiver is mounted in the truck and uses this cable);

2. A trailer-mounted winch containing 2,500 feet of largerdiameter cable rated to 250°C for transmitting current downhole; and

3. A modem transmitter and 6-channel receiver manufactured by Zonge Engineering and Research.

Researchers surveyed two coreholes in central Utah that UURI had drilled on a project funded by the Gas Research Institute, the State of Utah and several industrial partners. This area was used as a test bed because of its nearness to Salt Lake City and because, besides the core, a wealth of logging data was donated to the project by Schlumberger. Data analysis is in progress.

Researchers developed a preliminary algorithm and model results were used to design a multi-array cross- borehole system. UURI acquired and modified a logging system, and completed a field test in a shallow non-geothermal environment. A deeper test in a well documented geothermal environment is next.

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EXPLORATION TECHNOLOGY ! ' $ FY93 ANNUAL PROGRESS REPORT

Organizations

New Mexico State University

Industry Interest and Technology Transfer

Extent of Interest:

Possible power and greenhouse development at Rincon, NM; resource delineations

Masson S.W. Inc.

Milgro, Inc.

Greenhouse development at Radium Springs

Greenhouse development, Newcastle, UT

Unknown lease applicant

Utah Geological Survey

Oxbow Power Corp.

The Geophysics Group, and Transpacific Geothermal

Pilgrim Springs Corporation

Implications for Future Geothermal Development

Geothermal lease applicants, Thermo H.S. UT

Geothermal resource assessment

Siting drill targets at Carson Lake prospect.

Methodology and SP technique development

Possible development of Pilgrim Springs area, AK.

Enhanced self-potential techniques increase the required accuracy in siting drill targets for low- temperature utilization and for testing moderate- to high-temperature resources. This allows the pursuit of an aggressive exploration effort wherever geothermal power economics is attractive.

! Expected Outcome

~ = Sensitive exploration methodologies and algorithms, resulting in cost-eflective exploration and increased geothermal reserves.

= A spreadsheet to estimate SP cross-coupling coefficients from rock descriptions.

e An improved SP modelling code that can handle realistically complex geological models.

An evaluation of an innovative approach to SP data collection.

Publications and Presentations

Ross, H.P. and Witcher, J.C., 1992, Self-potential expression of hydrothermal resources in the southern Rio Grande Rift, New Mexico: Geothermal Resources Council Transactions, 16, 247-253.

Ross, H.P., Blackett, R.E., Shubat, M.A., and Gloyn, R.W., 1993, Self-potential and fluid chemistry studies of the Meadow-Hatton and Abraham Hot Springs, Utah: Geothermal Resources Council Transactions, v. 17, p. 167-174.

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Wannamaker, P.E., 1993a, Tensor controlled-source audio magnetotelluric survey over the Sulphur Springs thermal area, Valles Caldera, New Mexico, U.S.A.; implications for structure of the western caldera and for CSAMT methodology, University of Utah Research Institute Report DOE/ER/14083-2.

Wannamaker, P.E., 1993b, Fluids in the Earth's crust; Electromagnetic constraints on existence and distribution, in Fluids and Faulting, Proc. U.S.G.S. Redbook Conf., Fish Camp, CA, in press.

Mackie, R.L., Madden, T.R., and Wannamaker, P.E., 1993, Three-dimensional magnetotelluric modeling using difference equations - theory and comparisons to integral equations solutions, Geophysics, 58, 215-226.

Wannamaker, P.E., Pellerin, L., Trip, A.C., and Xiong, Z., 1993, Three-dimensional interpretation of short-offset loop electromagnetic data, paper presented at the International Workshop on Airborne Electromagnetic Methods (AEM), Dept. of Mining and G a l . Engr., Univ. Arizona, Tucson, AZ, Sept. 13-16, 1993.

Heat F/o w Studies

Background

Heat flow and temperatures at depth are needed to assess the potential for exploring and developing geothermal resources. Such data is particularly important to geothermal exploration groups which need improved accuracy in predicting subsurface temperatures. Correction of thermal conductivity and heat flow values can also be realized based on knowledge of subsurface flow of water. Estimates of basement heat production based on lithology are used to infer heat flow in areas of sparse direct measurements.

Approach

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Thermal conductivity values for the sedimentary section above basement were collected for the central and Eastern conterminous United States (see Figure 9). These conductivity values will be matched with their respective stratigraphic COhmns and existing heat flow data to Calculate the distribution O f telllperature at depth. Highly accurate heat flow measurements will be stored as digital, map-based data to provide reliable information over large areas of the United States.

figure 9. Generalized areal distribution of temperature gradients in the Rincon area. Simplified structural geology, and radon anomalies are also shown.

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Geothermal Developers

FY93 ANNUAL PROGRESS REPORT + - EXPLORATION TECHNOLOGY

Extent of Interest

Development planning using heat flow map.

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Researchers at Southern Methodist University completed data compilation for heat flow, rock type and conductivity to basement for the United States. This new compilation is at a spatial resolution of about 5 minutes (about 3 to 5 km) and allows estimation of temperatures, particularly in the eastern and central U. S . , with much greater precision than in the past.



The heat flow and temperature data can be used to plan and execute viable exploration strategies for future geothermal projects.

Expected Outcome

Priority drill targets for moderate and low-temperature resources at Newcastle, Woods Ranch, and irhermo in Utah; and at Rincon and Radium Springs in New Mexico.

Map-based heat flow and subsurface temperature data for the eastern and central United States.


Blackwell, D.B., et. al., 1993. Geothermal resource evaluation for the eastern United States based on heat flow and thermal conductivity distribution: GRC Transactions, v. 17, p. 97-100.

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FY93 ANNUAL, PROGRESS REPORT EXPLORATTON TECHNOLOGY

GEOCHEMICAL METHODS

Background

The primary objective of the geochemical investigations of geothermal systems is to develop techniques that will lead to a better understanding of the chemistry and fluid flow patterns within geothermal reservoirs. This information is needed at all stages of geothermal development, from early exploration to full exploitation. At the initial stage of a project, generalized hydrogeochemical models are used by the explorationist to interpret geochemical, geophysical and geologic observations in different geologic environments and to site thermal gradient wells. Later, detailed hydrogeochemical models help the developer by providing information on the natural state of the reservoir, which is needed as input for reservoir modelling. At the time researchers at the University of Utah Research Institute (UURI) initiated these studies, suitably detailed models of geothermal systems had not yet been developed.

This research directly addresses priorities established by the geothermal industry. The direction of current studies on liquiddominated systems reflects the results of a 1989 industry survey which reiterated the need for developing a better understanding of reservoir processes, properties, conditions, and boundaries in different geologic environments.

There were two important findings from earlier studies: 1) that fluid inclusion data could provide quantitative information on the reservoir, and 2) that fluid inclusion data could be combined with chemical analyses of geothermal fluids to extend the hydrogeochemical models to regions of the reservoir that could not be sampled directly.

High- to moderate-temperature liquiddominated geothermal systems may be broadly categorized as granitic, volcanic, or sediment hosted. Although geothermal systems share a number of common characteristics, recent studies conducted at UURI and at other institutions demonstrate that there are significant differences in the hydrogeochemical characteristics of geothermal systems in, for example, granitic and volcanic environments. There are several questions that are currently being addressed. These include: 1) What are the similarities and differences between geothermal systems in similar environments? 2) What physical and chemical boundaries are present within the reservoir and how can they be recognized? and 3) What is the extent and importance of reservoir processes such as boiling, mixing, and conductive cooling in different environments?

Objective

To refine existing hydrogeochemical models of geothennal systems in diferent environments, including vapordominated systems.

Approach

Researchers first demonstrated that fluid inclusions did record the chemical data that was required. Salinities and temperatures determined from the inclusions in paragenetically late minerals were compared to temperatures measured in the well bore and to the salinities of the production fluids to establish the relationship between the fluid inclusion data and the present conditions.

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FY93 ANNUAL PROGRESS REPORT I B EXPLORA~~N TECEINOLOGY

The second stage involved the application of fluid inclusions as a means of determining the CO, contents of the reservoir. Several approaches were taken to insure the validity of the work. Fluid inclusion measurements conducted at UURI were crosschecked using independently calibrated equipment at other institutions. Direct evidence for CO, in the fluid inclusions was sought and established by crushing individual samples. Computer models were developed to predict the characteristics of the inclusions under changing temperatures, compositions and gas contents. These predictions were compared with the measurements made on the inclusions.

In the third stage, fluid inclusion data is combined with results of fluid analyses to develop detailed hydrogeochemical models of the systems being studied.

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Figure 10. homogenization temperatures of the samples studied.

North-South cross section of the Cos0 geothermal system showing the average


The present work significantly expand@ upon earlier investigations. As a result, a detailed evolutionary model of the Cos0 geothermal system was developed. Previous studies had shown that the Cos0 geothermal system consists of a well defined, asymmetric plume that originates in the southern part of the field and then spreads laterally to the north (Moore et al., 1989, 1990) as can be seen in Figure 10. As the thermal fluids move away from the upwelling center, the top of the plume rises vertically from a depth of 1500 m in the core of the system to less than a few hundred meters in the north. New mineralogic data suggest that the geometry of the plume is related primarily to the presence of a narrow zone of partially sealed, steeply dipping structure that extends the len,oth of the field.

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Investigation results indicate that the main features of the system’s present thermal structure were already developed at the time the fluid inclusions were formed. These data show both the existence of the plume and the presence of a permeability barrier between the main production zone and the faults that fed hot spring deposits on the eastern side of the geothermal field. Comparison of the fluid inclusion and measured temperatures indicates that cooling has occurred along the top and margins of the geothermal system while temperatures have continued to increase within the core of the field. The apparent salinities of the fluid inclusions within the interior of the plume, however, were only slightly higher in the past than they are today. These compositional differences reflect dilution by ground waters and the sporadic flux of CO, generated by local boiling.

Cool, low-salinity ground waters extended over much of the present geothermal system during the emplacement of the thermal plume. Dilution of thermal waters occurred along the margins of the plume, producing strong gradients in the compositions of the mixed waters that were preserved in the fluid inclusions. In response to dilution of the thermal fluids and heating of the ground water, clays and carbonates precipitated along the margins of the reservoir. This mineralization reduced the permeabilities of the shallow fractures and formed an effective seal over the thermal system.


I Organizations

California Energy Company Far West CaDital

I Morrison KnudsedGuatemala

Calpine Inc. Ormat Mother Earth Resources Russian River Geothermal Cop. UNOCAL

Comisi6n Federal de Electricidad (Mexican National Utility)

Instituto Nacional de Electrificacion (Guatemalan National Utility)

J a m m e Geological Survey

Extent of Interest

Provided samples and production data

Funded research activities

Cost-shared studies

Cost-shared studies


This research will ultimately yield reduced costs for exploring and developing geothermal systems. This will be particularly beneficial to geothermal developments in granitic hosted reservoirs within the western U.S. Results from these studies are already being used by various groups including:

1) the U.S. Navy in its review of California Energy Company’s development program at Coso;

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2) Calpine Inc. in its exploration program of the Cos0 area;

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Expected Outcome

Basic hydrogeochemicd data needed for the development of conceptual modeIs in digerent geologic environments.

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Moore, J. N., Adams, M. C., Copp, J. F., The Geochemistry of the Cos0 Geothermal System: Data from Production Fluids and Fluid Inclusions, in review.

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FY93 A i i A L PROGRESS REPORT INDUSTRY-COUPLED DRILLING

BASIN AND RANGE EXPLORATION

Background

Most of the geothermal systems of the conterminous U.S. presenting obvious surface manifestations (e.g., hot springs, geysers, fumaroles) have been explored and evaluated. Some have been developed for electricity generation or for direct use applications. The geothermal community shares a perception that vast amounts of geothermal resources have yet to be identified in this country. Because of the lack of manifestations, finding these resources requires a major exploration effort. Unfortunately, at present the private geothermal sector does not have the financial resources for such a costly project.

DOE, in consultation with industry, decided that a first step in the search of these "hidden" geothermal systems would entail a review of field data from geothermal areas under exploitation in the Basin and Range Province (mainly in California, Nevada, and Utah).

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Objective

F To develop geological and conceptuaI models of known geothermalfields in the Basin and Range Province that could aid in planning and executing jirther exploration.

Approach

The approach entails participating in joint DOEAndustry studies of the Cos0 (California), Dixie Valley, (Nevada), Roosevelt (Utah), and Steamboat (Nevada) geothermal fields. Researchers will review existing field data, develop conceptual models of these systems, and appraise the effectiveness of various techniques in locating, characterizing and evaluating liquiddominated geothermal systems in the Basin and Range Province.

Idaho National Engineering Laboratory (INEL); Lawrence Berkeley Laboratory (LBL); Stanford and the University of Utah Research Institute (UURI) are conducting analyses of field data, exploration data and early reservoir testing data. This information could indicate what geological environments are most favorable for hosting geothermal resources, as well as what exploration and development techniques could be most successful for developing geothermal fields at lower costs.

Researchers at Lawrence Livermore National Laboratory (LLNL) and UURI are ais0 testing geophysical methods, most notably self-potential methods at several geothermal systems in cooperation with geothermal developers


INEL, in a collaborative effort with the Electrical Power Research Institute (EPRI), reviewed ten geothermal areas and producing fields to provide EPRI with typical or expected values for a range of reservoir parameters. EPRI will use this information to develop feasibility economics and a conceptual design for the next generation of geothermal power plants able to handle a wider range of resource characteristics. A letter report was prepared for EPRI which documented the findings and included the extensive bibliography used.

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Organizations

California Energy Company and Electric Power Research Institute (EPRI)

Utility Industry

Basin and Range Operators

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Extent of Interest

In kind contribution towards project.

Interested in the next generation of geothermal power plants that can operate more efficiently and at a lower life cycle cost.

Interested in improved management plans for existing fields, and reduced life cycle costs of existing and future developments.

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FY93 ANNUAL PROGRESS REPORT INDUSTRY-COUPLED D U G

INEL and UURI started a case study of the Roosevelt Hot Springs, Utah geothermal field with the California Energy Company. The extensive pressure transient data collected from 1978 through 1987 was reviewed. Preliminary analysis of select portions of this data were performed using the eclipse of interference technique to locate undetected boundaries. This technique was unable to resolve the location of undetected linear boundaries in the reservoir due to proximity of the responding wells to nearby, known linear boundaries.



The EPRI project will ultimately result in the next generation geothermal power plants that operate over a wider range of geothermal resource characteristics, possibly leading to a tripling of the on-line power in the U.S. by the year 2000 at a reduced life cycle cost.

The INELKJURI Roosevelt case study will result in an enhanced understanding of successful field development. Specific goals are integration of diverse sets of geological, geophysical, geochemical, and reservoir engineering data for use in future Basin and Range exploration and development projects. Experience gained at Roosevelt Hot Springs will result in improved procedures and tools for resource evaluation and characterization.

Expected Outcome

e Maps showing the most promising areas in the Basin and Range Province to explore for hidden geothennal resources, as well as the identification of the most effective exploration techniques.


INEL prepared a letter report for EPRI documenting the estimates of reservoir parameters.

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FY93 ANNUAL PROGRESS W R T INDUSTRY-COUPLED D W G

LONG VALLEY EXPLORATORY WELL

Much of the future geothermal development, in general, will depend on the presence of large thermal reservoirs in young silicic calderas. It is believed that very large heat sources exist in such formations as the Long Valley Caldera (the USGS circular 790 estimates 4800 quads within the caldera). So far, however, power on-line at Long Valley remains limited, in spite of significant commercial exploration, because coupling between the heat source and the hydrothermal system is not well understood.

On a broader scale, it is also uncertain that caldera heat sources, with much of their thermal energy in molten rock, can be reliably detected with surface measurements. Since Long Valley is one of the most thoroughly studied calderas in existence, it provides an ideal location for validation of the current surface data interpretation.

Finally, the scientific value of deep drilling at Long Valley is unique, in that access to the near-magmatic environment in a young caldera is available nowhere else. The existing well is already the deepest to penetrate the caldera, and drilling during the next phase is predicted to penetrate the basement rock’s brittlejductile transition zone, estimated to be at a temperature of approximately 350°C.

Objectives

b To resolve questions about deep fluid circulation patterns in the caldera.

b To test the hypothesis of the existence of large amounrs of thermal energy in young silicic calderas.

b To provide a realistic environment for testing advanced drilling hardware.

b To provide a unique scientific access to the near-magmatic regime and understand the formation and evolution of calderas.

Approach

The drilling and scientific activities on this well will be coordinated to satisfy a wide spectrum of needs defined by government agencies, the scientific community, and the geothermal industry. The project has already been supported with $1.5 million from the California Energy Commission, and cost sharing with industry will be pursued for the remainder of the project.

Although there are several leaseholders in the caldera, and many thermal-gradient and exploratory wells have been drilled, actual development has not been particularly active. The primary reason for this is the lack of understanding concerning fluid circulation in the deep caldera structure. None of the exploratory wells drilled to date have been much deeper than 6,000 feet, and analysis indicates that even a very large and hot reservoir at greater depth can be masked by lateral fluid flow above it. Drilling far enough, to give a better definition of the deep circulation patterns, will be an indispensable aid to further hydrothermal development in this region of extremely high thermal potential.

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FY93 ANNUAL PROGRESS REPORT INDUSTRY-COWLED DRILLING

Results from the hole will permit the following:

1) Assessment of the hydrothermal resource beneath the resurgent dome.

2) Investigation of the patterns and conditions of deep fluid circulation and heat transport below the caldera floor.

3) Determination of the amount of collapse and subsequent resurgence of the central portion of Long Valley Caldera.

4) Determination of the intrusion history of the central plutonic complex beneath the caldera, and establishment of the relationship of intrusive to eruptive events.

5) Tests of advanced drilling hardware in a rigorous, realistic environment.


Just before the beginning of the fiscal year (September 1992) researchers emplaced a downhole seismometer at a depth of 6,600 feet, and it continued to collect high-quality data well past the end of the calendar year. Although this data set has not been analyzed in detail because of budget limitations, it is notably clean and undistorted.

During phase I1 drilling in 1991 an equipment malfunction prevented a complete cement job on the 13-318 inch liner. This casing, run from 1,600 to 6,825 feet, was cemented from bottom to approximately 3300 feet, leaving an open channel from the formation between 3,300 and 2,568 feet (bottom of 20-inch casing) into the wellbore. The combination of this flow path and the open corehole at the bottom of the well produced ambiguous data on temperature logs and water level readings. It appeared clear that there was internal flow between these zones in the wellbore, but it was not obvious in which direction the flow was going. To satisfy BLM’s permit requirements, a major part of this fiscal year’s work was remedial cementing around the liner and a tie-back casing string from the top of the liner to surface.

Cement was squeezed at the bottom of the casing to plug the corehole and seal any potential flow, and into the liner lap to seal around the uncemented top of the 13-3/8 inch liner. Researchers pressure tested the cement joint to 3,000 psi (as required by the Bureau of Land Management), cleaned out excess cement in the wellbore, and ran a 13-3/8 inch casing from the top of the liner to surface. A high-pressure (5,000 psi) wellhead was welded to the new casing (as required by BLM for further drilling) and a new 12-1/4 inch hole was drilled to 7,188 feet. This latter drilling was done directionally, since the previous hole had deviated almost 5 degrees at 7,130 feet. Directional drilling corrected the 2.78 degree deviation at the 6,825 feet casing shoe to 1.5 degree at the bottom of the new hole. The Long Valley Exploratory Well is now prepared for extension to 14,000 feet either by conventional rotary drilling or by wireline continuous coring.

A final activity involved supporting two other Sandia projects aimed at improving downhole data transmission. One of these projects uses mechanical vibrations in the drill string to carry data bits, while the other investigates the survivability of fiber-optic cables with drilling mud pumped by it at high flow rates. Both projects were successfully completed, with encouraging results for further work.

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DRILLING TECHNOLOGY

Drilling

The high temperature, hard rock, and corrosive environments encountered with geothermal resources are hostile to drilling and the completion of exploration, production, and injection wells. Drilling and completion of geothemal wells account for much of the cost of generating electricity fiom such resources. The Drilling Technology task develops improved and economic drilling and completion technologies, specialized downhole instruments to measure reservoir characteristics, downhole devices to perform cementing operations and measure well flow rates, and advanced bits to achieve faster penetration rates.

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LOST CIRCULATION CONTROL

Background

Lost circulation is defined as the loss of drilling fluids to pores or fractures in a wellbore during drilling. This loss of fluids is expensive and causes problems related to hole stability and wellbore completion. Lost circulation accounts for 10 to 20 percent of the total cost of drilling a typical geothermal well. Well costs, in turn, represent 35 to 50 percent of the total cost of a geothermal project. Consequently, 3.5 to 10 percent of the costs of a typical geothermal project are attributable to lost circulation. If significant reductions in lost circulation costs could be realized, the cost of geothermal power could be reduced.

Objective

b To develop downhole and surjiace tools, materials, and techniques that can be used to reduce the cost of detecting, diagnosing, and treating lost circulation zones encountered in geothermal drilling.

Approach

Researchers identified eight technology areas for lost circulation research covering the various aspects of the problem: detection, diagnosis, and treatment of lost circulation zones.

Each technology area is investigated to identify those areas that have the greatest potential impact on lost circulation costs. Technology areas with significant potential impact are then further developed. Feasibility studies, conceptual design, laboratory scoping studies, detailed design, laboratory testing, and field testing are undertaken for each tool or technique investigated.

The project is organized in six phases:

Phase I

Phase II

Phase lII

Phase IV

Phase V

Phase VI

Entailed investigation of each of the eight technology areas. This consisted of literature searches, contact with industry, conceptual design, and analysis to evaluate the feasibility of developing a specific tool or technique and the potential lost circulation cost savings associated with it. A prioritization of technology areas was developed, based on the potential cost savings, development feasibility, and potential acceptance by industry.

Detailed design of hardwaremd procedures for downhole or surface use. The design process itself is an important component of feasibility evaluation.

Design and construction of laboratory facilities that may be needed for testing purposes.

Laboratory testing of downhole or surface hardware; laboratory testing is used to evaluate and refine hardware designs.

Field testing, in which designs and procedures are exercised and evaluated in the field.

Technology transfer, in which a tool or technique is made available to industry through publication of results and assistance in implementing the technology in the field.

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FY93 ANNUAL PROGRESS REPORT DRILLING TECHNOLOGY


Drillable Straddle Packer

The drillable straddle packer is a downhole tool for isolating and directing the flow of cement into a selected loss zone interval. The goal is to maximize the volume of cement delivered to the loss zone, and to minimize dilution of the cement remaining in the wellbore. Although straddle packers are currently available for open hole applications, they are seldom used for lost circulation applications because of their high cost. The low cost packer under development differs from conventional packers in three important ways: 1) the new packer uses low pressure, flexible fabric bags as the sealing elements above and below the loss zone; 2) it achieves inflation with the differential pressure that develops across the cement ejection ports during cement pumping; and 3) it is designed to be disposable, remaining in the wellbore after the cementing operation, to be drilled through after the cement hardens.

The goal set at the beginning of this project is to develop a flexible fabric bag withstanding a 40 psi internal pressure differential. It is believed that this goal was met during FY92 by using woven fiberglass-reinforced silicone rubber fabric and designing a flange/O-ring clamp that provides closure on each end of the fabric tube. Bags capable of withstanding pressures in excess of 40 psi were fabricated and tested; however, further testing in early FY93 showed that the bags sometimes fail at pressures between 30 and 40 psi. Although this would be a sufficient inflation pressure to accomplish the intended purpose of the packer, an alternate method of closing the ends of the fabric tubes was sought as a means of increasing the maximum inflation pressure and improving manufacturability of the packer bags.

It was discovered that Peterson Products Company of Wisconsin manufactures stopper bags for temporary blocking and sealing of pipelines during maintenance and repair. The end closures for these bags employ swaged aluminum end caps that appeared to be ideal for the drillable straddle packer. Peterson agreed to fabricate packer bags for the development project, and several bags were received and tested in FY93.

Laboratory testing of the bags with the Peterson swaged end closures indicates that a reliable maximum inflation pressure of 30 psi is attainable using the fabric selected two years ago. This allows the packer to be designed for a 20 psi inflation pressure with an appropriate safety factor. This should be sufficient to provide significant zonal isolation during the cement pumping process. The results of the bag development project include two designs that provide this capability: one (the flange/O-ring design) that can be fabricated by a machine shop, and the other (the swaged end cap) that can be manufactured by Peterson on a larger scale at lower cost.

In addition to burst tests, several flow-by tests were conducted with the fabric bags in FY93. In these tests, wellbore pressure differentials were established across the bag (above and below it), and the leakage rate between the bag and the wellbore was measured. It was found that the fabric bags provide a virtually perfect seal on a smooth wellbore, with no measurable leakage, at pressure differentials up to the bag inflation pressure. Tests were also conducted with a length of 5/8-inch half-round wood trim situated to run the entire length of the bag between the bag and the wellbore wall, to simulate a rough wellbore. It was found that even with such a significant obtrusion to seal around, the bag restricted flow between the wellbore wall and the bag to only 1 to 2 gpm with a driving pressure differential of 30 psi. These tests indicate that the fabric bags should be capable of providing significant sealing in open (uncased) wellbores.

Fabrication and testing of the packer’s shroud assembly was also conducted during FY93. The shroud assembly is a protective case that encloses the fabric bags during emplacement of the packer downhole.

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Once the packer is in place, a 1.5-inch;nylon ball is dropped do&n%the drillstring, where it is pumped downhole to engage in a piston that slides the shroud off the packer assembly to uncover and inflate the fabric bags. The piston assembly utilizes aluminum shear pins to hold the shroud assembly in place until the ball engages in the piston and pressure builds behind the ball to shear the pins. Laboratory testing has shown that the piston assembly operates reliably, requiring a nominal 160 (+/-30) psi to shear the pins and initiate shroud removal.

With successful testing of all packer components now completed, the next step in the development process is to demonstrate the operation of a full scale packer assembly using cement under simulated downhole conditions. It is believed that this is a prerequisite before field testing in order to demonstrate the utility and effectiveness of the packer under known, controllable conditions. Consequently, the design of a Packer Demonstration Facility was initiated in FY93.

The Packer Demonstration Facility will consist of an above ground, concrete structure employing three walls that contain a 15’xlS’x15’ volume of packed clay and gravel beds. The gravel beds, which simulate loss zones, will be connected to a plumbing system that saturates the beds with water and controls their relative pressures. The purpose of this is to simulate underpressured and overpressured conditions typical of lost circulation and production zones intersecting a geothermal wellbore. A concrete tube in the center of the packed volume will simulate the wellbore and provide realistic sealing surfaces for the packer bags.

A typical test in the Packer Demonstration Facility will consist of pumping a volume of cement, allowing the cement to harden, and excavating the clay and gravel to map the cement flow throughout the simulated rock formation. The effectiveness of the packer in isolating and filling the selected gravel bed while minimizing the volume of cement that remains in the wellbore and leaks into other gravel beds can then be ascertained. The facility can also be used to evaluate experimental cements and cementitious muds using large scale batches. The gravel zones can be heated to temperatures as high as 200°F to test temperature activation of the cements.

Rolling Float Meter

The rolling float meter is a device that measures the flow rate of drilling fluid exiting the well. This information is useful for detecting and quantifying lost circulation. The rolling ffow meter was developed and laboratory tested in FY90-91 and field tested in late FY91. In FY92, results of a six-week field test were analyzed to evaluate the performance of the meter relative to that of the other flow transducers that were also tested. The results indicated that the rolling flow meter is capable of much better accuracy in measuring outflow rates than are current conbercial transducers, and is also much more sensitive in detecting lost circulation and fluid influx.

Two conference papers and a Sandia report were written describing the development and testing results of the rolling float meter. Detailed design drawings of the meter were also released. The conference papers generated sufficient industry interest that a concentrated technology transfer effort was undertaken. Seven rolling float meter units were fabricated and loaned to seven different service companies for independent field testing and evaluation. In addition, one of the companies built five additional units for a comprehensive field testing program.

During FY93, one of the service companies requested a second rolling float meter unit so that it could simultaneously test two meters at different geothermal well sites. In addition, another company expressed interest in marketing the rolling float meter to the drilling industry.

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FY93 ANNUfi PROGRESS REPORT DRILLING TECHNOLQGY

A third company discontinued its testing program, citing insufficient repeatability with extremely heavy muds, up to 17 Ib/gal. This company, which built five of its own meters for testing, modified the design of the meter, using a different wheel shape and size than the one developed at Sandia. Sandia's development tests showed that repeatability is a function of wheel design; therefore, the conclusions reached by the company may be applicable only to its modified design. Furthermore, Sandia's laboratory testing showed no effect of mud weight for muds as heavy as 12 lb/gal. Sandia did not test heavier muds because they are seldom, if ever, used in geothermal drilling. Further investigation of this issue will be conducted over the next year.

Acoustic Doppler Flowmeter Evafuation

An improved method for measuring drilling fluid inflow rates to a well is needed in order to fully utilize the improved accuracy of the rolling float meter for outflow measurements. Currently, inflow measurements are made by measuring the mud pump stroke rate and assuming a pump efficiency to calculate flow rates. This method suffers from fluctuating pump efficiency and is notoriously inaccurate.

A potentially more accurate measurement technique is the acoustic Doppler flowmeter. This type of meter is attractive because it is non-intrusive with transducers clamping onto the outside of the pipe containing the fluid. This is a necessary characteristic for any mud inflow measurement technique because of the abrasive nature of the drilling fluid and the risk of pumping a dislodged transducer downhole if the mud erodes it loose. Acoustic Doppler flowmeters are routinely used in many industrial applications. Their use on drilling rigs, however, has not met much success, presumably because of noise and vibration problems. A field test was undertaken to evaluate the long-term performance of Doppler flowmeters on a coring rig and to determine if development work could be undertaken to improve their performance in drilling applications.

A coring rig at the Steamboat geothermal field was instrumented in the summer of 1993. Both the inflow and outflow lines were fitted with magnetic flowmeters and two types of acoustic Doppler flowmeters. The two types of Doppler flowmeters employed different Doppler-shift detection circuits. The magnetic flowmeters were used to provide an accurate measure of flow rates for comparison with the Doppler readings. Magnetic flowmeters are highly accurate but are expensive and have pressure limitations that do not permit their routine use on the larger drill rigs used to drill production-size geothermal wells.

Flow rates were recorded during the drilling of a 4,000 ft corehole over a period of six weeks. The results indicate that the Doppler flowmeters can be calibrated in the field to accurately measure flow rates, but their calibration tends to drift significantly over time. The cause of this drift is not clear. Noise measurements indicate that the acoustic noise generated by the rig equipment (mud mixing equipment, shale shaker, drillstring rotation) occurred at frequencies of 0-5 kHz. This is much lower than the frequency of the acoustic transducers (660 kHz), but it is on the order of the Doppler shift in frequency caused by the moving fluid. Modifications to the Doppler flowmeter filtering or transducer frequency may be necessary to overcome the possible interference caused by rig noise.

Plans for this project include working with the manufacturer to modify the flowmeter - if possible, to accommodate rig noise below 5 kHz. Sandia's Wellbore Hydraulics Flow Facility will be used to test any modifications. The facility has full scale flow capabilities with independent flow rate measurements. Rig noise will be simulated with mechanical shakers to determine the effectiveness of flowmeter modifications. Other nonintrusive flowmeters will also be evaluated and, if promising, will be tested in this facility.

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FY93 ANNU& PROGRESS REPORT DRILLING TECHNOLOGY

Organizations

Martin-Decker Totco Shlumberger-Anadrill Electro-Flow Control Ltd. International Logging Epoch Tecton Geologic

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Extent of Interest

Rolling float meter testing.

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Borehole Televiewer Fracture:$Characterization Stuay

The purpose of the borehole televiewer (BHTV) fracture characterization study is to develop techniques for using a BHTV to accurately measure the apertures of fractures associated with lost circulation zones. Although the BHTV has been in use for many years to locate fractures and to determine their spacing, dip, and strike, quantitative fracture measurement is not readily accomplished because of the effects of signal amplifier settings on the apparent size of features as seen with the televiewer. In FY90, Sandia developed a technique for determining the optimal amplifier settings for filtering out unwanted signal perturbations and displaying only significant fractures that may be associated with a loss zone. This work, based on laboratory experiments in fractured rock samples, resulted in a technique that appears to enable fracture thicknesses to be measured within 15 percent accuracy, as long as the fractures are at least 0.15 inches in thickness. Fractures as thin as 0.03 inches can be detected but not accurately measured.

During FY93, the new software developed for acquiring and displaying televiewer data was field tested in three wells. Two coreholes at the Steamboat geothermal area were logged. The smaller hole, 2.75 inches in diameter, tested the lower limit of the slimhole televiewer’s borehole-size capability. A 12.25- inch section of the Long Valley Exploratory Well tested the upper limit of its borehole-size capability. In both cases, the software and the tool functioned properly. Data resolution in the 1.25-inch hole was rather poor, although significant borehole-wall features could be delineated.

Other developments on this project include the acquisition of a faster computer for acquiring, displaying, and analyzing televiewer data. The higher speed was found to be necessary for performing real-time data reduction related to calculating fracture apertures. Significant effort has also been expended in overhauling and repairing the televiewer to keep it operational. Some of the wellbore logging done in FY93 tested the televiewer’s upper temperature limit of 150°C.

Cementitious Mud Testing

Planning was initiated on a proposed joint work with industry to evaluate cementitious muds for lost circulation control. A draft proposal was written for the project, which will include California Energy Corporation, Halliburton Services, and DOE, through Sandia National Labs. Laboratory and field testing of cementitious muds will be undertaken to determine their effectiveness in treating severe loss zones. A new well at the Cos0 geothermal field will be instrumented during drilling to detect and characterize loss zones and diagnose cementitious mud treatments. The cause of any failures will be determined and corrected, if possible. Effective treatment techniques will be further tested in other wells of opportunity to determine effectiveness under less controlled conditions. This project, if approved, will be undertaken as a project of the Geothermal Drilling Organization and will be cost-shared between DOE and industry.


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FY93 ANNUAL PROGRESS REPORT DRILLING "ECEINOLOGY

Halliburton Services Rolling float meter testing; cementitious mud evaluation

G n e r g y C o r p o r i t ion I Cementitious mud evaluation I


If found to be feasible and development is successful, the following products will result from this research:

Rolling float meter Drillable straddle packer BHTV fracture characterization software and hardware Drilling fluid flow testing procedures for lost circulation characterization Porous packer Cementitious mud formulations for lost circulation control Downhole injector system for cementitious mud deployment Rig-site expert system for assistance with detecting, characterizing, and treating lost circulation

All the tools and techniques under development in the lost circulation program have short-term industrial applications in geothermal drilling. Additionally, some of the technology has near-term application in petroleum drilling. For example, the rolling float meter has considerable petroleum industry interest because of its potential for detecting gas kicks often encountered in oil and gas wells.

Expected Outcome - A 30 to 50 percent reduction in lost circulation costs that would result in a one to jive percent I I reduction in the cost of a rypical geothedproject. I

Publications or Presentations

"Development and Use of a Return Line Flowmeter for Lost Circulation Diagnosis in Geothermal Drilling," Geothermal Resources Council Transactions, Vol. 16, October, 1992.

"Status of Lost Circulation Research," Geothermal Program Review XI, U.S. Dept. of Energy, Berkeley, CA, April 27028, 1993.

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MEMORY LOGGING TOOLS

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Background

Downhole logging and surface geological measurements have become a backbone for hydrocarbon reservoir analysis. Since the first recorded borehole measurements in 1927, advances in hardware and interpretative methods have produced an impressive series of successes. Some individuals envision that within five years there will be an industry-wide consensus regarding a multidisciplinary approach to reservoir definition. This approach will range from the petrophysics of individual pores at a scale of lo4 meters (0.004 inches) to surface geophysical investigations with investigative lengths of 102 meters (328 feet).

An effort of this magnitude is not a feature of the geothermal thrust in the United States. While some surface geophysical studies are used, these studies are limited, and there is a general lack of downhole measurements even though they are required to interpret surface studies, to extrapolate core data away from a hole, and to correct production difficulties.

An often obstacle to downhole measurements is the fact that tools used in low temperature formations are not compatible with the geothermal environment, and the cost of developing and maintaining a suitable tool suite exceeds the anticipated revenues from logging services. But a market can only be supported if measurements produce a meaningfd output. Since interpretative techniques developed for hydrocarbon reservoirs are not proven in geothermal formations, a second obstacle is the general inability to relate log data to meaningfbl information. In some respects, the development of a viable geothermal logging industry is impeded by the chicken-egg syndrome.

Objectives

b To develop quality tools using self-contained data storing computers (memory tools) so that measurements can be made simply in extreme environments withut the use of an electric wireline.

b To insure that the cost of tools and/or logging services is not prohibitive to the geothemal industry.

b To develop appropriate inversion algorithms that relate tool response to geothemal production parameters.

b To transfer tools and somare to the geothennal and geothennal support industries by involving industry personnel.

Approach

An inherent difficulty with "memory" tools is that an operator is forced to "fly blind." The new generation of tools will be "smart" in the sense that some decisions may be made by the tool itself through appropriate programming of the computer. A goal is to make this programming simple so that it can be done by inexperienced personnel.

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FY93 ANNUAL PROGRESS REPORT DRILCING TECHNOLOGY

Memory tools are relatively new, and prototype tools are costly. For example, the first slimhole (2 inch diameter), high-temperature (700°F) temperature measuring tool cost $58,000. This cost is too high for many anticipated applications. Presently, with improved technology and the use of a more practical approach to engineering design, similar tools should cost less than $lO,OOO. It is envisioned that this cost will drop even further.

An evolutionary step is to broaden the measurement capabilities by developing a modular tool that features a universal computerhattery section that may be attached to one or more sensor packages. While this vision is somewhat futuristic, it is feasible, and will result in further cost reductions.

Inversion algorithms relate a tools response, formation temperature, gamma ray count rate, etc., to formation parameters of interest. often these algorithms are proprietary. The intent of the Memory Logging Tool Program is to work with industry, to the extent possible, in the development of inversion algorithms. Interactions are envisioned with the U.S. Continental Scientific Drilling Program and the NSF Ocean Drilling Program.

The Memory Logging Tool Program consists of the following phases:

Phase I (past years) assessed the state of the art regarding downhole measurements in a geothermal environment. This work arose in the DOE/OBES Thermal Regimes studies that were done as part of the Continental Scientific Drilling Program. It was completed in 1991.

Phase 11 (past years) interactions with Geothermal Operators, particularly UNOCAL, and involved temperature measurements in industrial holes. The resulting data were given to the operators for their comment and criticism. Comments were always favorable, especially when it was noted that memory temperature tools could return in a few hours about two orders of magnitude more data that the operators had amassed in several months of work using rudimentary instruments. This phase was completed in 1992.

Phase III (present) interactions with suppliers of tool components, and the calibration of prototype tools. Also, overtures are being made to ultimate instrument users to insure compatibility with their needs.

Phase IV (future) will deal with the use of a memory tool suite in industry holes with the intent of developing appropriate algorithms for the reduction of tool data.

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Calibration of Memory-Logging Devices for Pressureflempera ture Tools

Memory loggers must be self-contained. This means that all measurements of voltage, frequency, or phase must be made remotely, and appropriate standards must be carried on board the tool. Stated otherwise, references traceable to U.S. National Standards must exist in extreme environments.

Secondary Sandia standards, traceable to the National Institute of Science and Technology, were used to calibrate the clock (frequency standard) on the Onset Model 5F computer as the computer was being temperature-cycled. It was found that the standard clock was unacceptable in that it possessed an

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FY93 ANNUAL PROGRESS REPORT DRILLING TECHNOLOGY Y

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unacceptable temperature dependence. A special clock designed for high temperature applications was put into the system. While this clock also exhibits a temperature effect, it is not as large as the original, and temperature effects can be mitigated with proper calibration. A similar situation occurred in the voltage-controlled-oscillator, a device that converts an analog voltiigBto a frequency. With proper care, the pressure measurements are now accurate to + /- 1 .O psi, and the temperature measurements to + /- 1.0"C. It must be emphasized that the quality control placed on the pressure/temperature measurements is a strong selling point with industry since different tools can be used at different times, while retaining investigators' confidence in the data.

Calibration of Spectral Gamma Tool

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The spectral gamma tool was designed and built by Geophysical Research Corporation, Tulsa, Oklahoma. Calibration of the tool is the responsibility of Sandia.

The calibration of spectral gamma tools must take into account hole-size effects, casing thicknesses, and the presence of fluids in the borehole. The initial calibration of the spectral tool was accomplished at the DOE-certified test pits at Grants, New Mexico. These pits contain known concentrations of potassium, and the daughter products of uranium and thorium. The spectra obtained in the pits were inverted to produce calibration numbers for the tool when placed in holes similar to the Grants holes (4 inch diameter, 0.25 inch thick steel casing, water filled). While these conditions are applicable to holes drilled with slimhole equipment, a further generalization of the calibration is needed to satisfy hole conditions more in line with those drilled by the geothermal industry. The more general DOE test pits at Grand Junction will be used in further calibrations.

De war/Pressu re Vessels

The Dewadpressure vessel is the one most costly item in a modem high-temperature logging system. Three systems were purchased from National K Works, Houston, and they were incorporated into the prototype temperature/pressure tools.

Field Tests of Prototype Pressure/Temperature Tool

The pressure/temperature tool was used to make logs of a DOE-sponsored hole drilled near Steamboat Springs, Nevada. The results of these trials were satisfactory. The tools were flown by commercial air carrier to the site. The first deployment was unsuccessful when a computing system powered up in a wrong sequence. A subsequent test returned all required data. Unfortunately, the pressure sensor was damaged on shipment back to Albuquerque; it is being replaced by a more robust model.


I Organizations I Extent of Interest I UNOCAL California Energy Co. Calpine NCPA

Interested in all areas of research on memory logging tools.

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The ultimate goal of the Memory Logging Tool Program is to establish a credited logging industry supportive of the needs of the geothermal industry. The first tool will be a low-cost temperature-pressure tool suitable for use in slim, diamond cored holes. The first few copies of the tool will be loaned to geothermal operators so that they may see the gains that are made when logs are run often. Even such simple logs will aid in reservoir evaluation and in establishing engineering solutions for such difficulties as lost circulation control.

The second tool is a spectral gamma device for the identification of Potassium, Uranium and Thorium. These elements are carried by hydrothermal solutions, and they can be used to identify fractures when they are precipitated on the wall rock. The tool can also be used to identify scaling conditions when it occurs in cased wells.

An ancillary program, not funded by DOE/GD involves the development of a high temperature fluid sampler. This DOE/OBES effort involves scientists from the Ocean Drilling Program. This scientific program will utilize industry wells for the testing of the new sampler device.

The Memory Logging Tool Program is starting to see a suite of tools moving into the fielding stage. Work is needed in the area of selling the concept of logging to geothermal operators. This latter effort suffered a setback when UNOCAL sold many of its holdings in California. New bridges to the geothermal industry are being established.

Ewected Outcome I 1 10 Memory logging tools capable of operating in high-temperature environments. 1

Presentations and Publications

Lysne, P. "Memory Logging Tools", Geothermal Program Review XI, U.S. Department of Energyhergy Efficiency and Renewable EnergylGeothermal Division

Lysne, P. "Evolution of Downhole Measurement Systems", JOIDES Journal, October, 1993.

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ADVANCED SYNTHETIC-DIAMOND DRILL BITS

Background

Geothermal reservoirs are typically found in or beneath hard, abrasive, and fractured formations. Because of this, geothermal wells are often difficult and expensive to drill; well costs represent 35-50 percent of the total costs of a geothermal project. Doubling a drill bit's penetration rate and life would reduce the time necessary to drill a geothermal well, resulting in an estimated 15 percent reduction in total well costs (a five to seven percent reduction in overall geothermal project costs). Development of the syntheticdiamond bit design will provide bit performance improvements for hard rock environments.

Drilling costs in soft to medium-hard formations were significantly reduced by replacing roller bits with syntheticdiamond bits, which drill faster and last much longer. For instance, drilling costs in the Gulf of Mexico have been cut in half in some cases by using PDC bits; cost savings of $lOO,OOO per bit run have been reported in the literature. The hard, abrasive, and fractured rock formations drilled to access geothermal reservoirs are generally considered beyond the capabilities of current syntheticdiamond bit technology. Roller bits (see Figure l l ) , which are generally used for this application, suffer from inherently low penetration rates, accelerated bit wear, and often severe loss of hole gauge and roller bearing failure. If the syntheticdiamond bit technology can be extended into harder rocks, it would have a significant cost-saving impact in the geothermal industry.

Objective

b To develop advanced syntheticdiamond drill bits which can drill hard rock formations faster and with a longer life than roller-cone bits.

Approach

Eight drill bit and cutter companies have teamed with Sandia Labs to work on five projects as part of a cooperative effort to advance the state-of-the-art in synthetic-diamond drill bit design and manufacturing. Each project explores different approaches to develop a syntheticdiamond cutter and bit design. Each approach builds on the respective companies.' capabilities and current product interests. Sandia assures integration of individual projects into a coherent program and provides unique testing and analytical capabilities where needed. A complete program plan is delineated in the Sandia Report (SAND93-1953) "Program Plan for the Development of Advanced Synthetic-Diamond Drill Bits For Hard Rock Drilling."


Completed a comprehensive plan for the Hard Rock Drill Bit Technology Development Program

Completed detailed statements of work for each company under the Hard Rock Bit Program, and

which includes five projects for joint research with eight different companies.

completed the cost-shared contracting process with each involved company.

Developed a facility for testing syntheticdiamond cutters for hard-rock drill bits. The facility utilizes a vertical lathe which can transmit enough force to the cutter to properly simulate the drilling process.

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FY93 ANNUAL PROGRESS REPORT DRTLLING TECHNOLOGY

Initiated testing of single PDC cutters in the facility; developed a baseline measurement with which to compare other cutters.

Figure 11. A tricone roller bit for geothermal drilling.


Oreanizations

Smith International Megadiamond Dennis Tool Company DBS, A Baroid Company Security Diamond Products SlimDril Hughes Christensen

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Amoco Production Research

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Industry Partners

Field test facility and PDC research.

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Implications for Future Geothermal Developmenk .%

This research will yield improved cutters and bits with near-term industrial applications for geothermal, natural gas, and petroleum drilling in hard formations including:

0 Polycrystalline diamond compact (PDC) cutters that more efficiently fail hard rock, are more impact- resistant, and able to survive the high loads associated with hard rock drilling.

An advanced thermally-stable polycrystalline (TSP) drill bit capable of handling the higher temperatures associated with hard-rock geothermal drilling.

0 An optimized claw PDC cutter design combining the abrasion resistance of diamond and the impact resistance of tungsten carbide.

0 An optimized Track-Set PDC bit that effectively reduces lateral vibrations and impacts in hard rock.

Emected Outcome

nw A five to seven percent reduction in the cost of a typical g e o t h e d project by doubling the penetration rate and life of the bit.


Program proposal presented for industry review at the Drilling Engineering Association Meeting, Houston, TX, February 18, 1993.

Program presented to DOE'S Bartlesville Project Office Contractor's Review Meeting, Eufaula, OK, July 18-22, 1993.

"Program Plan for the Development of Advanced Synthetic-Diamond Drill Bits for Hard-Rock Drilling, " Sandia Report SAND93-1953, Sandia National Laboratories, Albuquerque, NM, September 1993.

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FY93 ANNUAI, PROGRESS REPORT DRILLING " E ~ O O L O G Y

ACOUSTIC DATA TELEMETRY

Background

Collection of navigation data at the drill bit and transmission to the surface rig is done in real time in virtually every off-shore drilling rig in the world. Logging data is often included in this transmission. This technology is called "Measurement-While-Drilling." The hardware to transmit data from the drill bit to the surface is key to the success of the measurement-whiledrilling industry. Current commercial technology is based upon constricting the flow through the drill string. This service is expensive (about $lO,OOO per day) and, therefore, relatively inaccessible to the geothermal industry.

The transmission rates using mud pulse telemetry are also slow (< 1 binary bit per second), which limits the service primarily to collecting drilling navigation data. Telemetry with acoustical carrier signals propagating through the steel drill pipe offers the promise of greatly increased data rates. More comprehensive logging data can be transmitted in this type of system. Because of these advantages, acoustical telemetry was first attempted in the 1940's but, due to the complex wave physics associated with this type of data transmission, no successful commercial system has yet been developed.

Measurement-whiledrilling (MWD) is a critical industry to the development of many energy resources including geothermal energy. The MWD industry is in excess of one billion dollars in gross annual revenues. Today, the MWD service hinges on the ability to transmit data along the length of a subterranean well by a sequence of pressure pulses generating in the drilling fluid. It is virtually axiomatic that these data rates are a factor of 10 to 100 too slow to accommodate the customer demands for real-time transmission of drilling parameters and formation data. Acoustic telemetry can meet this need by transmitting data via elastic waves in the steel pipe of the drill string. Numerous advances have been made, including feasibility studies which demonstrate that even weak elastic waves will propagate over a mile in drill strings. This work has produced several patents, numerous technical publications and active industrial participation. Novel hardware has also been designed and successfully field tested.

I Objective

I b To develop a new data communications link for measurement-whiledrilling (MUD) operations I and to reduce economic uncertainties associated with the acoustic data telemerry system.

Approach

In Sandia's past work, researchers augmented the empirical approach of industry with a more systematic approach directed at the fundamentals of acoustic telemetry. Researchers assembled computer simulations, experimental data, and field test results which demonstrated the existence of acoustic transmission bands strongly correlated to theoretical predictions. Another past objective was to demonstrate that transducer arrays could be developed and used to directionally project and measure acoustic energy in the drill string. Several devices have been designated, built, patented, and licensed to Baker HughesDNTEQ, an industrial partner.

This project was originally conceived because of the principal investigator's familiarity with wave propagation in solids with periodic structure. It was quickly realized that the physical concepts,

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m93 ANNUAL PROGRESS REPORT DRILLJNG TECHNOLOGY

Organization

Baker Hughes INTEQ

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Cost-sharing and patent licensing.

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computer algorithms, and experimental methods that were developed by the principal investigator for studying stress wave phenomena i: $ssile hear shields could be directly applied to the telemetry problem. Throughout this work, exceptional correlations between'this model and field test data have been demonstrated. Recent analysis and field tests of the attenuation mechanism have yielded significant insight into this aspect of the problem. It is evident that the majority of signal loss is due to coupling between axial, torsional, and bending motion in the drill string.

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Much of the work on the transducer design, as well as the evaluation of array responses, is now in progress. A new downhole signal generator (the Oracle) is near completion. This equipment will be used to test signal modulation methods in test wells. Other future work will build upon the existing system code, the surface simulation facility, and the field test system. Transducers which can efficiently produce sound, but which are not an integral structural component of the drill string, will be designed and tested. More economical field test devices that collect information on attenuation and ambient noise will emerge. Finally, the surface simulation facility will serve as a testbed for full scale cancellation and repeater arrays.


In a recent experiment at the Long Valley Well near Mammoth Lakes, California, researchers confirmed a new aspect of the telemetry problem which has greatly increased expectations of success. Sandia researchers have shown that by simply reordering the pipes in the drillstring according to length, the effective transmission distance can be tripled. Therefore, single-stage transmission may be possible over distances of 15,000 feet. Coupled with this confirmation of the "pipe-length" effect, researchers also developed a model of the fundamental attenuation mechanism in drillpipes. This model leads the research team to believe that surface simulations of the telemetry system are particularly relevant to the actual drilling situations and are far less expensive than field tests.

The surface simulation facility has been assembled. Site development tasks included:

1) assembling several sizes and types of drill strings to a maximum length of 1500 feet;

2) calibration of a new downhole acoustic signal generator;

3) obtaining acoustic measurements using a new real-time, data acquisition and signal-processing system;

4) acquisition and preparation of a field-test instrumentation trailer for future field-testing of downhole hardware.


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FY93 AIUNUAL PROGRESS REPORT DRILUNG TECHNOLOGY


The results of this research will provide a technology base to reduce the economic risks of the industrial partner, allowing industry to invest in the commercialization of acoustic telemetry.

Near-term industrial applications include improvements in geophysical imaging while drilling (TOMEX) for Baker HughesflNTEQ and analysis and control of vibratory drilling methods (Sonic Drill-Water Development).

Ewected Outcome

s Increased data transmission rates of mud pulse telemetry that contribute to lower geothermal drilling costs.

19 Doubling or tripling of the h4WD Industry 3 gross income amounting to a potential $1 to 2 billion in short-term wowth of annual revenues.

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D.S. Drumheller, "Attenuation of Sound Waves in Drill Strings." J. Acoust. SOC. Am 94, October 1993.

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SLIMHOLE DRILLING FOR GEOTHERMAL EXPLORATION

Background

Although the vast majority of the drilling technology used in the geothermal industry is derived from the oil and gas industry, geothermal requirements are qualitatively different. There are hard, abrasive, and fractured rocks; high temperatures; and underpressured formations, frequently containing corrosive fluids. All these factors impose a more rigorous environment than that normally found in oil and gas drilling. The service and drilling tool industries have little incentive to address these problems, since the number of geothermal wells drilled in a year is about 0.1 percent of the corresponding number for oil and gas. This lack of commercial R&D is the primary rationale for DOE’S support of technology development.

A systems analysis of geothermal development identified drilling costs for exploration and reservoir assessment as a major factor limiting expansion of proven geothermal reserves. The geothermal industry (utilities and geothermal operators) needs to reduce these costs to be competitive in meeting expanding Western requirements for environmentally benign, alternative energy sources. Although slimhole drilling bas been shown to reduce oil and gas exploration costs by 25 to 75 percent, there is not enough geothermal experience to fully evaluate its cost impact. Using slimhole data to confirm a reservoir discovery is also less well-defined in geothermal than in oil and gas. Once demonstrated and documented, however, slimhole exploration will have an application to both the U.S. and international geothermal markets.

Objectives

w To correlate production and injection test data between slimholes and production sue wells.

b To transfer slimhole exploration drilling to industry so that it becomes an accepted method for geothennal reservoir identijication.

F To develop and validate a coupled wellbore-reservoir flow simulator which can be used for reservoir evaludon from slimhole flow data.

b To collect data from slimhole and production wells in existing geothermal Jields.

w To cooperate with industry in a cost-shared slimhole drilling program.

Approach

A working group including personnel from Sandia, Lawrence Berkeley Lab, University of Utah Research Institute, U.S. Geological Survey, and independent consultants focused on test procedures for this program. This group is involved to some-extent in all decisions affecting the direction of the research. In addition to the Geothermal Research staff of this program, other Sandia organizations such as the Fluid Flow and Transport, Computational Fluid Dynamics, and Thermal and Fluid Engineering Departments are providing significant support.

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Principal research findings this year were associated with an exploratory slimhole drilled at Steamboat Hills near Reno, Nevada. This was the first attempt to design a well and develop a strategy for testing and data collection, all aimed at verification of a slimhole’s utility. The well was successfully completed, just at the end of the fiscal year, to a depth of 4,001 feet and was extensively tested during and after drilling.

A major result with direct benefit to the operator was identification of a producing fracture with commercial potential. This fracture can be intersected by moderate deepening of an existing well and, based on modeling of flow results from the exploratory slimhole, would approximately double production from the existing well. The slimhole also demonstrated high temperature and permeability to a greater depth than previously known in this field.

Although analysis is yet incomplete, the data set is of generally high quality and is appropriate to the nature of the drilling done. The following information is available: downhole (pressure, temperature, spinner) and surface (wellhead temperature and pressure, flow rate, lip pressure) measurements during four series of production and injection tests; continuous core (99-t percent recovery) and lithology log; numerous temperature logs; daily reports from toolpusher and mud engineer; televiewer borehole images of the top 500 feet of the hole; complete cost breakdown; downhole and surface fluid samples; and a narrative report of the project.

Although there are ambiguities in the data caused by internal flow in the wellbore, downhole measurements during the flow tests are in good agreement with a wellbore model available at Sandia. Sandia is also working closely with LBL to analyze field data with their models and, possibly, to develop a synthesis of the tools for more accurate simulation.


Organization

Far West Capital

Extent of Interest I Drilling and testing the corehole. To compile and release complete drilling, testing, and cost data on the existing wells (3 slimhole, 12 production, and 5 injection), geologic information on the local area, and production histories for the wells and power plants.


Even preliminary results from this research can have immediate industrial impact if it encourages exploration or development. The shortest-term application would be the use of slimhole data for basic reservoir evaluations and as a support for financing by lending institutions. Clearly, the more widely this could be done, the more widely it would be accepted.

Current initiatives such as the Bonneville Power Authority agreement are a stimulus to geothermal development in previously poorly-characterized areas, which is an ideal setting for slimhole exploration

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techniques. But the overall level of activity in the industry will depend heavily on such global issues as energy prices and the national economy.

Ercpected Outcome

sir Guidelines for drilling and completing exploration slimholes.

= Recommended test procedures and strategies, including data requirements, for slimholes.

Improved downhole instrumentation to collect needed data.

a Data interpretation techniques, possib€y in the fonn of a PC-compatible flow simulator, which could be distributed at a nominal eqense to independent developers.

10 Publication of the analysis and experimental procedures which have led to the above products.


Presentation to DOE Geothermal Program Review; Berkeley, CA; April, 1993.

Presentation to Geothermal Industry Advisory Panel; Albuquerque; April, 1993.

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FY93 ANNU& PROGRESS REPORT DRILLTNG APPLICATIONS

GEOTHERMAL DRILLING ORGANIZATION

Background

Geothermal drilling technology is based on oil and gas technology. The service industry that provides drilling and logging equipment has, as its primary market, the oil and gas industry. Since the geothermal market is relatively small, modification of the technology for geothermal applications usually requires payment of development costs. Drilling and completing wells represent from 30 to 50 percent of the cost of putting geothermal power on-line. The Geothermal Drilling Organization (GDO) provides a mechanism for the geothermal industry to pool its resources when developing a product or service of direct (and usually broad) use to the geothermal industry. Projects are cost-shared by the Department of Energy (through Sandia) and industry.

Objective

b To develop drilling technology thut results in a new product or service for the geothermal industry.

Approach

The GDO is composed of geothermal operators and service companies. Potential projects are screened by an executive committee to ensure they will result in a new product or service in the near-term. Project proposals are then presented to the members at periodic meetings. Projects require at least two industry participating members with DOE (through Sandia). Cost sharing by industry is at least 50 percent and can be in cash or in-kind services.


Several GDO projects were active during FY 93. Major results include:

The high temperature borehole acoustic televiewer began commercial application in Indonesia, operated by UNOCAL.

Baker HughesDNTEQ evaluated the temperature performance of elastomers for downhole positive displacement motors operating with air.

A-2 Granthternational completed an improved stripper rubber design for geothermal wells.

A-Z Granthternational began designing a retrievable whipstock for geothermal well drilling applications.

BNL, UNOCAL, and Halliburton began a new project to develop advanced cements for geothermal applications.

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Organizations !,

A-Z Granthternational Baker HughesDNTEQ Calpine Halliburton UNOCAL

Extent of Interest

Industrial partners


Each GDO project is designed to develop a new product or service. Although all projects have not been successful in commercializing a product, several new capabilities that will facilitate geothermal development have been introduced including:

0 A high temperature borehole acoustic televiewer for operation up to 300°C.

A new configuration for rotating head seals with improved performance.

A downhole air turbine for geothermal drilling.

Ewected Outcome

IT Improved drilling technology that has a major impact on the cost of g e o t h e d power by lowering the cost of exploration and production drilling


"Hard-Rock Penetration-Overview", Geothermal Program Review XI, U.S. DOE, Berkeley, CA, April 21-28, 1993.

47


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Optimum geotheml production and injection strategies are vital to maintaining reservoir pressure and 4xtending the resource lifetime. Understanding both reservoir processes and changes in resemir pressure and chemistry as a result of continued production are necessary for efective reservoir management systems. The ExplorQtion Technology task combines laboratory and analytical investigations to develop &$?field-test tools and techniques necessary to understand, assess, locate, and define key reservoir parameters. Reservoir chemistry is studied and analyzed to develop models that enable prediction of corrosion and scale formation. Cost-shared studies with industry also attempt to pressure-stabilize The Geysers reservoir, and to mitigate chemistry-related problems there.

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m93 ANNUAL PROGRESS RJPORT RESERVOIR TECHNOLOGY

RESERVOIR ANALYSIS

Background

Geothermal developers must understand fluid and heat flow within geothermal reservoirs to properly develop and operate geothermal fields. They must also understand how the chemistry of a system changes through time. A fundamental problem in characterizing geothermal reservoirs is lack of understanding of fracture and porosity patterns and their influence on multi-phase flow. Limited knowledge of the evolution of geothermal systems also hinders development of accurate models.

Geothermal resources are complex systems. In order to optimize production from reservoirs, developers must have accurate models of geothermal systems ahd the ability to predict the consequence of changing the operational parameters of the system. To develop accurate conceptual models developers must understand the genesis and evolution of geothermal systems, the fracture and porosity patterns which control fluid flow in the reservoir, the nature of multi-phase flow in fractured systems, and the chemistry of geothermal systems through time.

Objectives

b

To develop models for the flux of magmatic fluids and heat into geothermal systems.

To improve understanding offractures, veins, and breccia cements as reservoir controls in active geothermal systems.

To better understand hydrothermal reservoir characteristics and processes, and to identify the critical phenomena in geothermal systems located in diflerent geological and hydro-geological environments.

b

b

b

b

To collect thermodynamic data needed for accurate modeling of geothermal systems.

To develop more accurate conceptual and numerical models of geothermal reservoirs.

To develop improved dual-porosity models for simulating the behavior of fracrured reservoirs. I

Approach

Researchers at the University of Utah Research Institute (UURI) are carefully characterizing cores from various 6ortions of active, high-temperature geothermal systems. They are also investigating the use of various new borehole imaging techniques for determination of in situ stress orientation, as well as determining fracture attitudes, apertures, and degree of mineralization. Another promising research approach is the use of imaging techniques to study h e geometries and internal textures of fractures and miscellaneous pores in geothermal cores.

Researchers at Lawrence Berkeley Laboratory (LBL) and the Idaho National Engineering Laboratory (INEL) are analyzing field data from geothermal systems located in different geologic and hydro-geologic environments, and developing or improving reservoir engineering techniques to identify and characterize

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FY93 ANNUAL PROGRESS REPORT RESERVOIR TECHNOLOGY

Organizations

the physical and chemical processes in geothermal reservoirs. Data on U.S. and foreign geothermal fields is gathered and analyzed. Results of analysis and predictions are discussed with researchers from industry, universities and federal and state organizations. Researchers are conducting theoretical and laboratory studies of phenomena associated with multiphase (steam, liquid and non-condensible) flow in porous and fractured rock masses, and are developing mathematical techniques to improve the modeling of heat and mass transport in liquid- and vapordominated reservoirs.

Extent of Interest

Researchers at Oak Ridge National Laboratory (ORNL) are studying selected chemical equilibria. Of particular importance are the liquid-vapor distribution of HCl, aluminum speciation, liquid-vapor isotopic distributions, and bisulfate ionization.

Comisidn Federal de Electricidad (CFE)

UNOCAL and LBL

U.S. Geothermal companies

Improved practices and tools for .description and management of volcanic-hosted reservoirs.

Cost-share fractured media project in FY 94.

Improved simulation tools for reservoir management and monitoring.

I

Reservoir Analysis


Preliminary parametric studies at INEL indicate that pressure and saturation transients in fractured porous media can be simulated with a modification of the Warren and Root model, typically used in a conventional dual-porosity simulator. Flow in fractured media was simulated using fine grid methods looking at explicit fractures. These studies considered wide ranges of reservoir properties, and provide the basis for developing useful expressions to couple flow in fractures and rock matrix in fractured media, thereby improving simulation capabilities of fractured geothermal reservoirs.

INEL began a collaborative effort with Mexico’s Comisi6n Federal de Electricidad (CFE) to improve knowledge of volcanic-hosted geothermal reservoirs. A week-long workshop on reservoir simulation was held in Morelia, Mexico, and extensive data on Los Azufres was shared between CFE and INEL. An initial reservoir description and preliminary model of Los Azufres was developed during the workshop for CFE engineers to further enhance. Additional collaboration is anticipated between INEL and CFE on other geothermal resources in volcanic-hosted environments.

INEL started a new project to evaluate the use of earth tides in slim holes and estimate important reservoir parameters such as conductivity and storativity. These parameters are typically not measured in a slim hole due to the small wellbore diameter, which precludes the use of traditional flow testing and pressure transient analysis.


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-93 ANNUAL PpOGREsS REP0


The INEL fractured media project will develop a modification to the conventional dual-porosity reservoir simulator that will improve simulation of pressure and saturation transients in fractured media. It will also reduce the CPU usage to perform the matrix-fracture calculations. Such a tool improves the accuracy for simulating fluid flow in a large number of geothermal reservoirs worldwide. The use of earth tides to measure reservoir parameters in slimholes will result in an evaluation technique and a

.software package to conduct both forward and inverse analyses of tidal information.

The INEL collaborative effort with CFE promotes a win-win relationship which provides technology transfer to CFE colleagues and, in return, provides a greater understanding of volcanic-hosted geothermal systems to the U.S. industry for application in a Cascades type geothermal environment.


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Organizations

UNOCAL

Other Geothermal Developers


INEL lead a two day workshop on the use of TETRAD for advanced users at the annual GRC conference in Burlingame, CA. In addition INEL presented four technical talks. n

1)

1 Extent of Interest

' a Cost-sharing to jointly complete this research.

1 Expressed interest in the results of the project. 1

Improved Dual-Porosity Models for Simulating the Behavior of Fractured Geothermal Reservoirs


LBL developed a new method for simulating fluid flow in fractured geothermal reservoirs. The method is more accurate than the widely-used Warren and Root model and has been incorporated into a computer module compatible with the MULKOM/TOUGH family of reservoir simulators.

y !! !I Implications for Future Development-

LBL will develop a fdter, less computer-intensive, b d low cost method to simulate the complex mass and heat transfer occurring in geothermal reservoirs !'between fractures and neighboring rock mass.

Publications and 'Presentations Ii

Zimmerrnan, R.W., Chen, G., Hadgu, T. and Bodvarsson, G.S., 1993. A numerical dual-porosity model with semianalytical treatment of fracture/matrix flow. Water Resources Research, Vol. 29, No. 7, pp.

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Organizations

UNOCAL

Zimmerman, R.W., Hadgu, T., Chen, G. and Bodvarsson, G.S., 1993. Development of a dual-porosity model for vapordominated fractured geothermal reservoirs using a semi-analytical fracture/matrix interaction term. Proceedings 18th Workshop on Geothermal Reservoir Engineering, January 26-28, 1993, Stanford, CA (in press).

Extent of Interest

Contributed core samples and expressed high interest in the research.

Flow Visuaization and Relative Permeability Measurements in Rough- Walled Fractures

Calpine Corporation Northern California Power Agency Central California Power Agency


Expressed high interest in the research.

LBL studies have shown that the relative permeability behavior of fractures is similar to that of porous media, with even stronger flow interference at intermediate saturations and, that two-phase gas-water flows in fractures are prone to non-steady cycling-type behavior.


Oxbow Geothermal Corporation California Energy Company Magma Power ComDanv

Expressed moderate interest in the research.

Implications for Future Development

LBL research will yield a better understanding of phenomena associated with the simultaneous flow of steam and water in geothermal reservoirs hosted in fractured rock masses. Improved knowledge on multiphase flow in fractured geothermal reservoirs will enhance the capabilities of geothermal field operators to plan, optimize, and manage production and injection operations. Values of permeability and other physical properties of cores obtained from The Geysers geothermal field will also become available.


Persoff, P. and Pruess, K., 1993. Flow visualization and relative permeability measurements in rough-walled fractures. Proceedings Fourth Annual International High-Level Radioactive Waste Management Conference, April 26-30, 1993, Las Vegas, NV, Vol. 2, pp. 2033-2041.

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Organizations

U.S. and Foreign field developers

Conceptual and Numerical Models of Geothermal Reservoirs

Extent of Interest

Provided field data and expressed high interest in the research.


The 1986 LBL numerical model of the Nesjavellir field in Iceland predicted adequately the behavior of many production wells during the 1987-91 period. However, because of the short calibration time, the model needed to be recalibrated to improve the match between the observed and computed flow rate, as well as the pressure and enthalpy data.

Numerical modeling studies of injection of liquid water into vapordominated geothermal reservoirs confirmed the existence of a very efficient heat transfer process in vapor zones due to the development of heat pipes (water and vapor counterflow) and of an increase in the water saturation near the injection point. These studies also showed that: 1) in relatively high-permeability systems, single-phase liquid zones prevail, with convection providing the energy throughput, 2) in lower permeability systems a two- phase liquiddominated zone develops, and 3) for regions with high heat flow, a high-temperature single- phase vapor zone can develop below a typical vapordominated zone. Understanding the heat transfer process is key to maintaining optimum energy production from geothermal reservoirs.



The U.S. geothermal industry will be provided with reservoir models that can be used for field case studies to develop: 1) initial development programs for systems that are still in their characterization and evaluation stages, and 2) preliminary reservoir management plans for systems in their development stage. The use of these models will help illustrate: 1) the pros and cons of different reservoir development and exploitation strategies, and 2) the methodology for recalibrating computer models that predict the future behavior of fields to be studied. Such information helps avoid the pitfalls encountered by others during the different stages of,a geothermal project.


Bodvarsson, G.S., et al., 1993. Accuracy of reservoir predictions for the Nesjavellir geothermal field, Iceland. Proceedings '18th Workshop on Geothermal Reservoir Engineering, January 26-28, 1993, Stanford, CA (in press).

Lai, C.H., Bodvarsson, G.S. and Truesdell, A.H., 1993. Modeling studies of heat transfer and phase-structure of two-phase geothermal reservoirs. Accepted for publication in Geothermics.

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' Organizations

U.S. and Foreign organizations

International Cooperation

Extent of Interest

Updated information and field data.


U.S. companies interested in developing geothermal abroad

LBL developed a simulation model of the Cerro Prieto, Mexico, geothermal field to analyze the effects of large-scale injection. The model was transferred to the Comisidn Federal de Electricidad, operator of the field.

Expressed high to moderate interest in the project .


Increased international cooperation will facilitate development of field case studies on exploration, development, and exploitation of geothermal systems with different geological and thermodynamic characteristics. Data on the characteristics of geothermal fields abroad will be made available to the U.S. geothermal industry.

Direct lines of communication will be established with foreign organizations in charge of the development of geothermal energy. This will provide the U.S. geothermal industry access to updated information on geothermal activities worldwide and facilitate U.S. companies and U.S. technology to penetrate markets in countries interested in developing geothermal energy.


Antunez, E., Lippmann, M. and Marquez, R., 1993. Numerical study on the brine injection effects in the CPI production area of Cerro Prieto. Lawrence Berkeley Laboratory internal report. Presented in April 1993 to the Comisi6n Federal de Electricidad of Mexico.

54

FY93 ANNUAL PROGRESS REPORT - RESERVOIR TECHNOLOGY

Characterization of Fracture and Vein-Controlled Porosity and PermeabiFty in Active Geothermal Systems


The ability to handle large amounts of data using electronic media can improve the efficiency of collecting and archiving reservoir data. Increasingly, geothermal exploration is taking advantage of core drilling because of lowered costs of production wells and increased lithologic information that can be realized through core analysis. This research concentrates on image analysis of reservoir core samples. Images of whole or slabbed core can replace traditional photography and offer a means of analysis that was previously only qualitatively available.

Data is collected using either a still or video imaging camera. Images are annotated to describe lithology and identify important features (see Figure 12). Color enhancement techniques are used to emphasize or classify important features such as veins, fractures, or matrix porosity. This in turn is used to establish the statistical distribution of these features in the core.

-1 Adsorption Interface Solid Mineral = Pore Space

figure 12. Processed scanning electron microscope image showing an adsorbed water layer as white.

Image analysis can also be accomplished at the microscopic level. This approach was used to document the character of permeability in cores from The Geysers, and simulate the process of adsorption. Several techniques are useful depending on the objectives of the project. Pore space can be injected with a doped epoxy and then analyzed under laser light through a confocal microscope. Fluorescence of the epoxy

55


Organizations

UNOCAL

Geysers Geothermal Russian River Energy Company

allows pore space to be easily distinguished from rock. The laser light penetrates the rock matrix so that the path of the permeability can be imaged. This resulted in a method to statistically analyze the distribution of porosity around fractures.

Extent of Interest

Contributed core samples, use of this method in their Sarulla project in Indonesia.

Contributed core samples.

Volume Percent

50 loo 150

Feature Size (microns)

Figure 13. Volume percent void space as a function of chord length for a sample from well Prati State 12.

The size and shape of pores is the objective of digital image analysis using the scann,.ig electron microscope (SEM). Core samples from The Geysers have allowed quantification of pore sizes (see Figure 13). Digital simulation of adsorption suggests that even the most intricate pores have only negligible capability of containing significant adsorbed fluid reserves. The principal finding is that, at adsorption thicknesses of 10 to 100 angstroms, adsorption would not be a significant process in the retention of liquid reserves at The Geysers. Efforts to increase the life of the reservoir must be based on fluid injection.


... - -. .. ... . . . . . . . . . . . . . -. . . . . . . . . . . . . . . . . . . .. -. - . . .. . . - . . . . . . -. . -


,* * .


Archiving and manipulating core images and associated digital data using a personal computer will be possible. The advantages are: 1) data can be more effectively transferred within a company and between researchers; 2) core features, such as veins, can be isolated, allowing statistical treatment; and 3) images at,microscopic scales can be contained in a database, allowing interpretation of pore space or the description of permeability. This archiving system should be equally applicable in certain oil fields or in various underground waste-storage repositories.


Nielson, D.L., Nash, G., Hulen, J.B., and Tripp, A.C., 1993. Core image analysis of matrix porosity in the Geysers reservoir. 18th Workshop on Geothermal Reservoir Engineering, Stanford University, preprint.

Thermodynamics and Phase Relations in Granite Melts


Researchers are investigating the phase relations and thermodynamic mixing properties of synthetic granite ("haplogranitic") melts to develop a low-pressure (500 rp(bars) 5 4000) thermodynamic model.

This new experiment emphasizes: (1) determining the solubility of water in haplogranitic melts, (2) acquiring new and more accurate data on the boundaries of crystal-melt phase fields in haplogranitic systems, (3) ascertaining the amounts and chemical compositions of silicate materials dissolved in aqueous fluids that have equilibrated with haplogranitic melts, and (4) measuring the equilibrium partitioning of Na and K between haplogranitic melts and coexisting alkali chloride-bearing aqueous fluid.

Current research is focused on developing a thermodynamic model for albite-quartz-water (ab-qz-w) melts at 2500 bars, 730-10oO"C. Results of preliminary Fermodynamic modeling indicate that hypersolidus phase equilibrium data tightly constrain the excess free energies of melts. It can be shown that a total of six chemical-potential-equivalence equations hold at the intersections of the L(Ab), LW) and L(Qz) boundary curves. Consequently, experimental data that delimit these intersections can be used to evaluate the mixing parameters of an empirical thermodynhic model for ub-qz-w melts.

Industry Interest and Technology Transfer I I

NIA Y

!,

Implications for Future Geothermal Dejelopment

There are numerous locations world-wide where it is evident that geothermal resource areas are linked genetically to granitic magmatism. Two phenomena that relate directly to this link are heat transfer from granitic magmas to superjacent geothermal areas and mingling of magmatic-hydrothermal fluids with meteoric waters. In the latter event, it is important to recognize that the initial chemical compositions

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FY93 ANNUAL. PROGRESS REPORT RESERVOIR TECHNOLOGY

of magmatic hydrothermal fluids are strongly influenced by the bulk composition and thermodynamic mixing properties of the granitic magma, and that various geochemical reactions can potentially produce significant changes in the compositions of these fluids prior to the time that they mix with hot, circulating meteoric waters.

These and other geochemical issues pertinent to the granitic intrusion-geothermal system association have been addressed qualitatively in numerous field studies of active and fossil geothermal fields. However, complementary experimentalltheoretical investigations, which are essential for quantitative modeling of igneous-geothermal processes, are few in number. A significant fraction of the data required to perform such modeling can be obtained from systematic experimental and theoretical investigations of the phase relations and thermodynamics of synthetic systems that serve as analogs for natural granitic rocks.


NIA

€xperimental and Theoretical Investigation of the Production of HCI and Some Metal Chlorides in MagmatitYHydrothermaI Systems


Plutonic areas of California thought to be analogous to those associated with geothermal systems have been sampled and analytical work has begun to predict the chemistry of solutions emanating from the magmas during cooling. Experimental work with artificial melts was conducted. The experimental data suggest that aqueous mixtures associated with melts of high aluminum content are more acidic. This dependence has implications on the pH of solutions associated with geothermal systems.


NIA


The evolution of geothermal systems and the effects of magmatic gases h, these systems will be better understood.


fluids on the canemistry of

Piccoli, P.M., and Candela, P.A., 1993a. Apatite in felsic rocks: a model for the estimation of initial halogen contents in the Bishop Tuff (Long Valley) and Tuolumne Intrusive Suite (Sierra Nevada Batholith) Magmas. Accepted for publication in American Journal of Science.

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FY93 ANNUAL PROGRESS REPORT RESERVOTR TECHNOLOGY

Piccoli, P.M., and Candela, P.A., 1993a, 1993b. Magmatic-hydrothermal volatile history of the Billy Lake-Rush Creek Volcano-plutonic Complex, Ritter Range, Sierra nevada Batholith, California. EOS- Transactions of the American Geophysical Union, v. 74, p. 333-

Williams, T.J., Candela, P.A., and Picoli, P.M., 1993. An experimental study of the hydrogen-sodium exchange between a high-silica rhyolite and a two-phase aqueous mixture: comparison of results at 1 kbar, 800°C and 1/2 kbar, 850°C. EOS-Transactions of the American Geophysical Union, v. 74, p. 322.

Expected Outcomes from the Reservoir Analysis Project

e New tools for eflective targeting of productive geothermal-reservoir rocks, while allowing more content reservoir modeling through more realistic constraints for fracture/ breccia/ vein- controlled porosity and permeability.

Better understanding of geothermal reservoir processes in response to production and injection of fluids. 7% allows development of reservoir management plans that extend the resource commercial lifetime, and augment the amount of energy that can be extracted economically.

sir Improved geothermal reservoir models facilitating better reservoir management strategies. Such models may allow up to one-third fewer dry holes to be drilled resulting in an unquant@ed amount of additional energy to be produced from reservoirs.

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FY93 ANNUAL PROGRESS REPORT IRESERVOIR TECHNOLOGY

BRINE INJECTION

Background

In most geothermal fields, the spent, cooled brines must be injected back into the reservoir, primarily to maintain reservoir pressure and secondarily to avoid surface and ground,water pollution. The location of injection wells within the three-dimensional network of fractures that form a reservoir are critical to the successful exploitation of a field. Field experience and simulation ;studies of the Brine Injection Program have also shown that the amount of injection in any well is also critical to successful injection strategies.

In order for industry to successfully plan injection strategies, it must hav;e an understanding of the flow paths within the reservoir, and the interaction between the reservoir and the injected fluid. The brine injection program is providing industry with the tools necessary for injection planning.

Objectives 1

b To identicfir and test compounds for use as geothermal tracers.

b To reduce uncertainty in geothermal reservoir engineering design by improving reservoir analysis techniques.

b To develop the capability for accurately modeling and predicting two-phase flow and heat transfer during injection in geothermal reservoirs.

Approach

UURI researchers are evaluating the utility of various compounds as tracers and have identified the immediate need of organic tracers for the geothermal industry. T h k e compounds must have the following characteristics: 1) nontoxic, 2) thermally stable or easily quantifiable rates of decay under geothermal conditions, 3) minimal rock-tracer interaction, 4) detectable at low conditions, and 5) are relatively inexpensive. Researchers tested geothermal tracers currently used by industry and the most commonly used groundwater tracers for stability in a geothermal environment. Although very few groundwater tracers proved to be stable at high temperatures, the results 11ed to generalizations on which types of compounds might be most stable in a geothermal environment. After identifying tracer compounds and testing them in the laboratory, field testing is carridd out in cooperation with the geothermal industry.

Researchers at Stanford University are investigating several well test configurations, including flow into fractures and flow in a reservoir with a two-phase or gas zone overlying a liquid zone. In addition, researchers are looking at simultaneous analysis of pressure transient and tracer test information and are developing mathematical models, most of which require solutions using computer-based techniques.

INEL and LBL researchers are improving existing reservoir simulators used to model geothermal systems and using them to predict the effects of injection, and to optimize injection strategies in operating fields.

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FY93 ANlWAL PROGRESS REPORT RESERVOIR TECHNOLOGY

Organizations

Stanford Geothermal Program Industrial Affiliate Companies (PG&E, UNOCAL, Calpine, and NCPA)

Well Test4 and Tracer Analysis

Research Status and Findings I : ;

Extent of Interest

Contributed financially to the research program.

Researchers developed numerical techniques for the simultaneous interpretation of pressure transient and tracer tests. An intermediate paper was written outlining the physical consequences of heterogeneities on the results of well tests. Researchers are now considering tracer tests in heterogeneous reservoirs.

'

- Organizations Extent of Interest

UNOCAL, Central California Power Agency, and Calpine Corporation

Northern California Power Agency

Pacific Gas and Electric Company

Contributed field data and expressed high interest in the research.


Expressed moderate interest in the research.


Improved methods for testing wells and interpreting tracer test returns in geothermal fields will be developed and made available to the geothermal industry.


Deng, X.F., and Home, R.N., 1993. "Well Test Analysis of Heterogeneous Reservoirs," paper SPE 26458. Proceedings of the 68th Annual Conference of the Society of Petroleum Engineers, Houston, TX.

FY93 ANNUAL PROGRESS REPORT ' RESERVOIR TECHNOLOGY


Data analysis techniques and computer models to dksign field management procedures will be made available to the geothermal industry. Such models will allow to optimize the extraction of heat stored in the reservoir rock masses, reduce reservoir pressure drawdown, and avoid (or minimize) thermal interference between injection and production wells.

I Publications and Presentations

Pruess, K., 1993. Dispersion of immiscible fluid phases in gravitydriven flow: A Fickian diffusion model. Submitted to Water Resources Research.

Pruess, K. and Enedy, S., 1993. Numerical modeling of injection experiments at The Geysers. Proceedings 18th Workshop on Geothermal Reservoir Engineering, Stanford, CA (in press).

Pruess, K. and Wu, Y.S., 1993. A new semi-analytical method for numerical simulation of fluid and heat flow in fractured reservoirs. SPE Advanced Technology Series, Vol. 1, No.2, pp. 63-72.

Tracer Development


Last fiscal year, UURI researchers laboratory tested rhodamine WT at high temperatures. Rhodamine WT is ari orange fluorescent groundwater tracer that was used in geothermal tracer tests during the early 1980's with equivocal results. Initial laboratory experiments indicated that rhodamine WT decays fairly rapidly above 230°C, with a rate that is also sensitive to the anions present in the solution. Evidence from groundwater tracer experiments has also indicated that Rhodamine WT may adsorb to a much greater extent than fluorescein.

Previous field tests indicated that significant adsorption may not take place at the temperatures and rock types common in geothermal systems, and that there are many geothermal systems below 230°C. A field test was designed to examine both the decay rate and degree of adsorption of rhodamine WT under actual geothermal conditions. Both rhodamine WT and fluorescein were injected together into an injection well in the Steamboat Hills geothermal system in Reno, Nevada. Nine production wells were monitored, and all showed a significant amount of tracer return. No evidence of rhodamine WT adsorption was found in the reservoir. UURI researchers are examining tracer data to determine the decay rate of rhodamine WT under field conditions, and a reservoir model incorporating the return profiles is being created at LBL.

To date researchers have identified and tested several types of tracers that are stable in geothermal systems. Some of these tracers were used in actual field tests to study their behavior and to obtain additional information about the reservoir, such as the effective temperature along the injection-production flow path. Fluorescent tracers will be identified and tested, and The Geysers research on two-phase tracers will be extended to two-phase reservoirs.

Efforts will be spent on deciphering what other information can be gleaned from tracer behavior during injection tests, such as reservoir steam fractions and the relative speeds of steam and water in the reservoir.

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Organizations

Far West Capital

Domestic and international geothermal industry and electrical utilities (UNOCAL, California Energy Co., Russian River, Calpine, NCPA, PG&E, and CFE)

DOE Waste Isolation .

Geothermal Resources Council United Nations

International Atomic Energy Agency

ENEL (Italian National Electrical Utility)


This research will ultimately yield a wide variety of tracers suitable for the variable phases, conditions, and temperatures found in geothermal systems. The tracers that have been developed are already being used by industry.

Extent of Interest

Furnished injection and production wells, rented injection equipment, and provided samples from all of the production wells for nine months.

Inquiries on tracer usage and choices, cost- shared tracer tests, short courses.

Tracer data to analyze the hydrology of waste repositories.

Short courses on geothermal tracers for developing countries.

Tracer tests' in developing countries.

Inquiries and paid lectures on tracer usage and choices; use at Larderello.


Researchers presented a poster at the 1993 Geothermal Resources Council meeting entitled "Rhodamine WT as a Geothermal Tracer - A Field Test at Steamboat Hills, Nevada."

Expected Outcomes from the Brine Injection Project

st Better tools to plan and operate injection programs.

e Decreased drawdown and increased longevity of the geothennal resource.

a Estimates of increased injection at the southeast Geysers suggest that doubling the current rate of injection may add as much as 3 to 7percent of additional power capacity.

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FY93 WAL PROGRESS REPORT , RESERVOIR TECHNOLOGY

BRINE CHEMISTRY

Background

To minimize corrosion and mineral precipitation difficulties during geothermal production, operators must have knowledge of the chemistry, the potential chemical reactions caused by temperature and pressure, and the composition changes caused by production of the geothermal system. Further, fundamental chemical data are needed for predicting chemical and permeability changes in reservoirs and plant facilities involved in the extraction of geothermal energy.

Objectives

b To collect fundamental chemical data needed for predicting chemical changes in reservoirs and plant facilities involved in the extraction of geothennal energy.

b To develop geochemical models that can be used for predicting changes in chemistry and that he@ geothermal operators minimize corrosion and mineral precipitation problems.

b To collect thennodvnamic data needed for accurate modeling of geothennal systems.

Approach

Researchers at the University of California at San Diego (UCSD) are developing chemical models that predict the equilibrium relations of the brine equipment-rock system during production. Researchers review geochemical literature and carefully validate the data so that accurate equilibrium systems can be established based on experimental data. Using Piker theory, researchers are developing binary and ternary models from the data and, from these systems, are determining the chemical behavior of geothermal systems. These models are entered into a computer based code that can predict system behavior at the elevated temperatures, pressures, and total dissolved solids content of geothermal systems. The computer code is updated on an annual basis and is made available to interested geothermal developers through a training session conducted by UCSD researchers.

Researchers at the Oak Ridge National Laboratory (ORNL) are studying selected chemical equilibria including the liquid-vapor distribution of HCl, aluminum speciation, liquid-vapor isotopic distributions, and bisulfate ionization. A series of solute volatility experiments were completed for the HCl + NaCl system.

Liquid Vapor Distribution of HCI (aq)

Research Status and Findings /

Researchers conducted laboratory experiments to determine the volatility of HCl from electrolyte solutions containing NaCl plus HCl, MgCl,, MgCl, plus NaCl and CaCl,. The alkaline earth ions Ca2+ and Mgz+ were examined to assess the effect of their hydrolysis on the distribution of HCI to the steam phase.

64

FY93 ANNUAL PROGRESS REPORT RESERVOIR TECHNOLOGY .+. 'pi + i@ %(;

Rigorous thermodynamic models aie being applied to the results, ba;Ced on known activity coefficients of the solutes in the liquid phase and assumed full association (neutral species) in the vapor phase.

Highlighted conclusions include:

Very low pH values (PH <3) required to produce 100 ppm chloride at wellhead from HCI partitioning. Above 300"C, this value is nearly independent of temperature.

0 Neither MgCl, nor CaCI, hydrolyze strongly enough at high temperatures to give HCl concentrations as high as 100 ppm in steam.

0 At temperatures above 300"C, NaCl partitions to the vapor phase in amounts sufficient to give 100 ppm chloride in steam from concentrated brines.

0 Above 300"C, brines containing NaCl and hydrolyzable cations (e.g., Ca and Mg) could produce acidic steam with chloride concentrations near 100 ppm.


NIA i,

Implications on Future Geothermal Development

The production of acidic and corrosive steam is becoming an increasingly serious problem limiting the production of steam at The Geysers geothermal reservoir. Wells drilled recently in the northwest Geysers have produced steam at higher temperatures (> 300°C) than usually found in the main body of the reservoir ( ~ 2 4 0 ° C ) . Often these wells produce high levels of chloride as hydrochloric acid at the wellhead, with observed levels greater than 100 ppm in some cases. This acid-chloride-bearing steam is extremely corrosive to piping and well casings, leading in severe cases to loss of production within a few days. Further, the question of potential production of acidic steam in older wells at The Geysers, as the reservoir dries out with continued production, is of great long-term significance in the operation of the resource. The current study, partitioning of HCI over both single electrolyte solutions and over brines likely to be encountered in the reservoir, will address the problem of acidic steam production in deeper, hotter wells and the projected behavior of the reservoir with further production.

I


J. M. Simonson and D. A. Palmer, 1993. "Liquid-Vapor Partitioning of HCl(aq) from 323 to 623 K", Geochim. Cosmochim. Acta, 57, 1.

J. M. Simonson and D. A. Palmer, "A speciated model for the distribution of HCl(aq) between liquid and vapor phases to the solvent critical conditions," Geochimica Cosmochimica Acta (in press).

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FY93 ANNUAL PROGRESS REPORT I RESERVOIR TECHNOLOGY

Aluminum Speciation and Hydroxide Solubility


In order to quantitatively model the solubility of aluminum minerals in geothermal systems, a detailed examination of the low-temperature (0-100°C) geochemistry of aluminum was required. This information was critical to address the recharge zone phenomena and to serve as an anchor for extrapolation and assessment of the high temperature data.

Highlights of the current research include:

0 Measurement of the solubility of gibbsite - Al(OH), - 0-5 molal NaCl;+HCl brines from 30-70°C to establish the thermodynamic properties of AI3+. An additional result iwas the discovery that this ion does not significantly interact with chloride ion, the most abundant ligand in geothermal brines.

0 Gibbsite solubility measurements in 0-5 molal Na-K-Cl-OH solutions from 6-80°C to establish the thermodynamic properties of Al(0H);. This ion and A13+ are the dominant aluminum species in brines at all conditions, except in a narrow pH range in which the intermediate A l ( 0 H P species predominate.

0 Potentiometric titrations to establish the formation constants for the next most important aluminum species, Al(OH)’+, in 0-5 molal NaCl brines from 25-150°C.

0 Gibbsite solubility measurements in 0.1 molal NaCl at 50°C in the presence of organic buffers (acetate) bistris and tris) over the pH range 3-9. This work revealed significant complexation of A13+ by acetate and of Al(0H); by bistris. After correction for complexation, the resultant noncomplexed solubility curve was analyzed to extract the stability constant for Al(0H);.

All of these results were combined to provide a complete and quantitative model for the speciation of aluminum and the solubility of gibbsite in 0-5 molal NaCl brines from 0-100°C. A provisional model for aluminum speciation to 350°C in low salinity brines was also developed by combination of the results with recent published literature data on the solubility of boehmite -A100H - at high temperature.


N/A


Alteration of geothermal reservoir rocks, weathering and soil formation, contaminant transport, sedimentary diagenesis, and ore foundation, are all influenced by fluid buffering and permeability changes caused by the interaction of aluminum silicates, oxides, and hydroxides with circulating aqueous fluids. The thermodynamic properties of many aluminous minerals are well known, but the aqueous chemistry of dissolved aluminum remains a controversial subject, due to the slow kinetics of dissolution and precipitation of aluminous phases, the persistence of polymeric species in aqueous solutions to low total aluminum concentrations, and the extremely low equilibrium solubility of aluminum minerals at near- neutral pH. The monomeric speciation of aluminum in natural waters will be determined quantitatively and unambiguously over a wide range of solution compositions and temperatures.

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FY93 ANNUAL PROGRESS REPORT RESERVOIR "JXHNOLOGY


Palmer, D.A. and Wesolowski, D.J., 1993. Aluminum speciation and equilibria in aqueous solution. Part 111. Potentiometric determination of the formation constants of Al(OH)'+ in 0-5m NaCl solutions from 25 to 125°C. Geochimica et Cosmochimica. Acta, vol. 57, pp. 2929-2938.

Palmer, D.A. and Wesolowski, D.I., 1993. High temperature potentiometric measurements of hydrolysis and metal complexation reactions. Proceedings of the 4th International Symposium on Hydrothermal Reactions, Nancy, France, Aug. 31-Sept. 3, A.A. Balkema, Rotterdam, pp. 173-176.

i?: {* :$ tip z

Wesolowski, D.J. and Palmer, D.A., 1993. Aluminum speciation and equilibria in aqueous solution. Part V. The solubility of gibbsite at 50°C in O.lm NaCl solutions with hydrogen ion concentration buffered in the 10" to range. Geochimica et Cosmochimica. Acta (in press).

L- V Distribution of Isotopes


Researchers experimentally determined the effect of dissolved ions on the partitioning of oxygen iind hydrogen isotopes between (a) geothermal brines and steam, and (b) geothermal brines and minerals at elevated temperatures. Liquid-vapor partitioning studies of oxygen and hydrogen isotopes, both pure water and salt solutions (NaCl, KCI, MgCI,, CaCl,, NqSO,, MgSO,, and their mixtures), were conducted from 25 to 350°C. Experiments assessing the effects of dissolved NaCl on the oxygen isotope partitioning between water and minerals, CaCO, and Mg(OH),, were conducted at 300°C and 1 kbar, and at 200°C and 20 bar, respectively.

V-L PartitioninP bure water): The experimental results obtained and most of the low-temperature literature data of oxygen and hydrogen isotope partitioning were fitted to single equations, which cover the range from 0°C to the critical temperature of water (374°C). The isotopic compositions of steam and water samples collected from geothermal fields, especially the ratio of A6D/A6180, can also be used to evaluate temperatures of phase separation.

V-L Partitioning (brines): In the single salt solutions studies (0-6 molal NaCl solutions at 50- 350°C, and 0-3 molal KCl, 0-5 molal MgCl,, 0-5 molal CaCl,, 0-2 molal Na$O,, and 0-2 molal MgSO, solutions at 5O-10OoC), hydrogen isotope fractionation factors between the salt solutions and vapor are appreciably lower (up to 20 Ym) than those between pure liquid water and vapor (in the order pure water > Na$O, > KCl 5: NaCl > MgSO, > MgCl, 2 CaCIJ.

Except for KCl solutions at 5O"C, the oxygen isotope fractionation factor between the salt solutions and vapor were higher (up to 4 %o) than, or very close to, that for pure water.

The observed oxygen and hydrogen isotope salt effects in the single salt solutions are all linear with molality of the salt solutions, and can be fitted to a simple equation as a function of molality and temperature.

67


The isotope salt effects in several mixed salt solutions of the system Na-K-Mg-Ca-C1-SO,, including those that mimic natural geothermal brines (Salton Sea brine), are exactly additive of the effects of single salts separately.

0 Mineral-Brine ExchanPe: Results of isotopic exchange experiments, of calcite-water at 300°C and 1 kbar show that the equilibrium oxygen isotope fractionation factors are 7.2k0.5 and 7.5k0.4 YOO for calcite-pure water, and 6.9k0.6 %o for calcite-5 molal NaCl solution. The oxygen isotope effect of 5 molal dissolved NaCl (approximately 0.4 to 0.5 %o) is consistent with results of 1 molal NaCl solution-vapor equilibration at 300°C.


NIA


The distribution of the stable isotopes of hydrogen (H, D) and oxygen (l60, '*O) among the fluid and mineral phases in geothermal systems are a result of the primary origin of these phases (clastics, diagenetic and alteration minerals, meteoric and magmatic fluids, etc.), the time-temperature history of fluid-rock interaction, the integrated fluidhock ratio, and phase separation processes such as mineral dissolution and precipitation and separation of steam and other gases from heated brines. Indeed, the limited number of previous studies have suggested large and complex salt :effects in the 100-350°C range that, if neglected, would result in gross misinterpretation of stable isotope data from active and paleo- geothermal systems. Results from this research clearly demonstrate that the isotope salt effects in many salt solutions are too large to be ignored for isotopic studies of geothermal brines. For example, the stable isotope ratios of steam in geothermal reservoir are highly dependent on the chemical composition of the boiling geothermal brines, and these differences must be taken into account to evaluate temperatures of the reservoir brines. Errors in calculated reservoir temperatures of as much as 50 to 100°C could result.


Horita, J., Wesolowski, D.J. and Cole, D.R., 1993. The activity-composition relationship of oxygen and hydrogen isotopes in aqueous salt solutions: I. Vapor-liquid water equilibration of single salt solutions from 50 to 100°C. Geochimica Cosmochimica Acta 57, 2797-2817.

Horita, J., Cole, D.R. and Wesolowski, D.J., 1993. The activity-composition relationship of oxygen and hydrogen isotopes in aqueous salt solutions: 11. Vapor-liquid water equilibration of mixed salt solutions from 50 to 100°C and geochemical implications. Geochimica Cosmochimica Acta 57, 4703- 4711.

Horita, J. and Wesolowski, D.J. Liquid-vapor fractionation of oxygen and hydrogen isotopes of water from the freezing temperature and the critical temperature. Geochimica Cosmochimica Acta (in press).

68

FY93 ANTWAL PROGRESS REPORT RESERVOIR TECHNOLOGY

Geochemical Models ;,:> : ;.!


UCSD researchers developed a highly accurate equation of state (EOS) for the NH,-H20 binary system. This equation predicts thermodynamic properties with near experimental accuracy. It has been incorporated in the user oriented GEOFLUID package and will be used in exploration and power system design.

Extensive PVT data for pure NH, were published before 1960. The data cover temperature and pressure ranges from -20 to 300°C and from 1 to 1100 bar. Considering the excellent extrapolation property of the EOS developed, the pure NH, should be reliable from 1 to 1500 bar and from -20 to 400°C. Using this end member EOS, together with an EOS for H20 published previously @uan, M+ller, Weare), researchers parameterized a gas mixing rule based on the existing phase equilibrium data. It should be noted, because of the variation between some of the data sets, the data were carefully reviewed before parameterization.

Researchers evaluated the EOS of Anderko and Pitzer for the NaCI-H,O system in the critical region of H,O. This NaCl-H20 model has been programmed and is ready to be included in the GEOFLUID package. Modeling of the ternary system, NaCI-H,O-CO,, has began.

Evaluation of the binary and ternary solution parameters needed to describe the chemical behavior of seawater-type (Na-K-Ca-Mg-CI-SO,-H,O) brines to high temperature (250'C) was completed. Temperature functions for the chemical potentials of the stable and many of the metastable single and double salts found in the binary and ternary subsystems have been established. The model is in excellent agreement with the solubility data for all of these salts. Parameterization and validation of the seawater model without magnesium has been carried out and reported in earlier publications.

Validation of the new temperature functions for the magnesium interaction' solution parameters and for the chemical potentials of the magnesium containing salts is being carried out by comparing model predictions with solubility data in complex solutions. Results to date indicate highly reliable prediction of the data as a function of temperature (T- depends on data availability) and concentration (to I = 30m). The effect of data availability on model prediction is being assessed in the validation process. Transition temperatures for the various salts in the seawater system are calculated to be within 10% of laboratory results. Also, a temperature function for polyhalite, a triple salt found in the seawater system, has been included in the model. i

Researchers simulated' bulk water properties and water clusters using several models of water-water interactions identified in a comprehensive survey:. Through the "first principles" simulation program researchers are developing appropriate new phenomenologies to describe the complicated brines and gas phases that are common to geothermal systems.

This year progress was made on nonpolar gas mixtures. Remarkably, the simulations describe PVT with errors within a few percent of the experimental data. This suggests that at least qualitative behavior of condensed water systems can be obtained by molecular dynamics simulations using these potentials. Experimental data collection for this kind of system can be reduced by such an appropriate simulation program.

I

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FY93 ANNUAL PROGRESS REPORT i RESERVOIR TECHNOLOGY

Organizations

Geothermal Operators

The thermodynamic properties of non-aqueous mixtures in the system COa-CH,-N, were simulated. The results of the simulations compare well with experimental data. As far iiS the researchers know, this is the first simulation of such complex mixtures. A phenomenology model has been developed which succinctly summarizes these results.

A more user-friendly interface has been incorporated into the TEQUIL, and now SUN, PC and Macintosh versions are ready for distribution. Instead of specifying all system parbeters in a file (composition, temperature, pressure, etc.), the user can alternatively have the prograni prompt for input information or use an independent input file, as in the prior version of TEQUIL. A beta version of this program has been distributed, comments solicited, and an updated version of thd code (beta) made available. Experience suggests that this change will greatly increase the transfer oflthe code to geothermal users.

Extent of Interest

More than ten companies attended the modeling and code use training and received copies of the codes. Several of @em use the code to predict scaling during operations.

Researchers have also made an X window graphical user interface via the MOTIF tool kit for the workstation version of TEQUIL. This code has just been finished and distribution to selected users is proceeding. While this version presently requires a workstation, it is anticipated that PC and MAC technology will soon be brought to the point that will allow transfer of ithis version to more generally available machines.

The GEOFLUID model was requested by the UNOCAL company for yse in oil and gas exploration problems. Distribution of the developed computer codes has continued,. through requests and through workshops. The new interactive version of the code has been well received and a considerable number of diskettes distributed. Comments on the performance are being collected and improvement in the interactive implementation has been made.

UCSD staff prepared and presented a tutorial on the GEOFLUID model to the Geothermal Resources Council on October 9 (San Francisco). The new interactive version of the code was presented and there were a number of requests for copies.

I

UCSD staff gave a workshop on a NaCl-KCl-MgC1,-H,O model applicable to potash production for the Potash Corporation of Saskatchewan, Canada. At this workshop (Nov. 18), diskettes of ,the model were distributed. This corporation has promised to continue their limited support of the modeling program at UCSD.


Canadian Mining Industry A consortium of potash mining companies support the project since the model improves the productivity of their potash mining operations.

Petroleum Industry Various oil and gas companies use the model to address exploration problems.

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FY93 AN"UU PROGRESS REPORT RESERVOIR "ECHNOLOGY

Expected Outcomes from the Brine Chemistry Project

e A computer code capable of modeling complete geothermal systems and that allows geothermal operators construct user-friendly geochemical models to minimize corrosion and mineral precipitation.

Geochemical models thut can be used for predicting changes in chemistry and that help geothennal operators minimize corrosion and mineral precipitation problems.

n

Implications for Future Geothermal Development kh? *.* +& i &l

Geochemical models and computer-codes that can be used by ghthermal operators to understand and control the chemistry of their geothermal systems to avoid well scale, scaling of surface equipment and corrosion. Available versions of the codes are currently being used. As the code becomes more complete it will be of immediate use on a broader variety of problems.


Mdller, N., Weare, J., Duan Z. and Greenberg, J., 1993. "Brine (Solution, Solid and Gas Phase) Modeling ' Program, Advanced Technology to - Aid the Economical Development of Geothermal Resources. 'I Proceedings of Geothermal Program Review XIII.

Duan, Z., Mc#dler, N. and Weare, J., 1993. "The Prediction of Water Properties Using RWK2 Potential, from Clusters to Bulk Water," in preparation for Geochimica et Cosmochimica Acta.

Duan, Z., Mdller, N., DeRocher, T. and Weare, J.H., 1993. "Prediction of Boiling, Scaling and Formation Conditions in Geothermal Reservoirs-Using Computer Programs TEQUIL and GEOFLUID, " in preparation for Geothermics, manuscript available.

Duan, Z., Mdller, N. and Weare, J.H., 1993. "The Molecular Dynamics Simulation of Non-Aqueous Gas Mixtures," in preparation for Geochimica Cosmochimica Acta.

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FY93 ANNUAL PROGRESS REPORT I RESERVOIR TECHNOLOGY

HOT DRY ROCK RESEARCH

Background I

Hot Dry Rock (HDR) is by far the largest geothermal energy resource/ in the United States with the resource base amounting to about a million quads (total U.S. energy consumption is less than 100 quads annually). A technique to access and extract this energy was patented in 1974 by inventors at the Los Alamos National Laboratory. It entails first drilling into hot rock and then using hydraulic fracturing techniques to create a reservoir by opening natural joints in a large volume of rock (see Figures 14 and 15). One or more additional wells are drilled into the reservoir at some 'distance from the first and the system is operated by pumping water down one well, through the resedoir, and up the other well(s). The water extracts heat from the rock as it passes through the reservoir.: At the surface, the hot water may be used to produce electricity or for direct thermal applications. It is then recirculated through the reservoir to mine more heat.

Since 1974, work on this project has been directed toward demonstrating and perfecting the HDR heat mining technique. A small system was developed in the early years to show that the process was feasible. During the 1980s, a larger underground reservoir was created and a surkace plant was constructed. A long-term flow testing program (LTFT) was carried out during 1992-1993 to prove that, in addition to being possible, the technology is also practical. The most important issues addressed are sustainability of energy delivery, water consumption, impedance to flow, and long-term operational characteristics.

figure 14. a) Original conceptual design of the Phase I1 reservoir. b) View of the Phase I1 reservoir.

72

Figure 15. Simplified schematic of the Fenton Hill surface plant.

Objectives

b To evaluate the sustained pevormance of the Fenton Hill Phase II HDR reservoir with regard to system operating characteristics including energy production, thermal lifetime, flow impedance, and water loss.

b To evaluate the economics of the technology in light of the most recent technical developments.

b

b

To confirm the environmental acceptability of the technology.

To evaluate the various modes of operation of HDR systems, such as continuous, cyclic, and high backpressure, for eflciency, power potential, effect on reservoir lifetime, and operational reliability.

To demonstrate +DR technology applications at a second site in a direrent geographical setting and with diferent geological characteristics.

To evaluate the concept of multiple production wells per single injection well as a means to signijicantly improve system pevormance and economics.

b

To develop reservoir modeling, seismic analyses, tracer techniques, and logging technology, and demonstrate their utility in the development of HDR systems.

73


Objectives (continued)

b To improve the performance of drilling and completion operations under conditions typical of hot dry rock environments.

b To form a partnership under industry leadership and develop a HDR facility to produce and market electric power.

Approach

The HDR team has constructed a pilot scale reservoir and a surface plant built to industrial specifications. Long-term flow testing conducted during 1992-1993 prolvides an experimental basis for refining cost estimates, documenting operational water needs, demonstrating that sustained energy production from HDR is possible, and identifying remaining problems to be attacked. A second site will be developed with private industry leadership to produce and market electricity from HDR at competitive prices. Subsequently, direct thermal uses of HDR energy will be demonstrated. These efforts will set the stage for additional commercial HDR facilities built entirely with private funding on the basis of sound investment considerations.

The Los Alamos National Laboratory Hot Dry Rock research consists of five phases:

Phase I (1974-1980) consisted of a scientific demonstration of the possibility of extracting useful amounts of energy from HDR.

Phase I1 (1981-1986) involved the creation of a much larger, deeper, and hotter underground system. It entailed the development of drilling and completion equipment to construct the system and analytical tools to adequately characterize it.

Phase I11 (1987-1991) consisted of the construction of a surface facility, built to industrial standards, to enable the underground system to be evaluated under conditions simulating commercial operations.

Phase IV (1992-1994) the present phase, is concerned with demonstrating that HDR can provide energy on a sustainable basis with reasonable quantities of water use. It involves long-term flow testing (L") which will prove that it is practical to commercialize the technology, provide operating experience with which to refine economic models, and point up remaining problems to be addressed in the construction of HDR plants producing energy for sale. The final part of this phase will consist of wrap-up testing conducted to complete the findings of the initial long-term testing, and/or testing suggested by industry to provide an improved basis for the development of an industry-led effort to build and operate a power-producing HDR-facility.

I

Phase V (1995-1999) will involve the construction, by an industry-led effort, of an HDR plant to produce and sell electricity at competitive costs (1995-1998) and of an HDR facility to provide energy for lower quality resource for direct thermal applications (1996-1999). These plants can be fully competitive in both electricity generation qnd thermal energy production. At this point, the technology will have both the certainty1 of success and the operating economics to make commercial HDR facilities attractive for full private sector support.

74

. . . . . . . . . -. . - . . . . . . . . - .. . -. . -. - . - . . . . . -. . - . . . . . . . . . - .. . . . . . . . - . . . . .. - . -

P E

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0


Test results during 1992-1993 were extremely positive. After a total of about eight months of circulation over a one-year span, no signs of thermal drawdown were observed. In fact, tracer evidence indicated that the circulating fluid was continually coming in contact with additional hot rock as the test proceeded. Water losses declined throughout the test, eventually reaching only seven percent of the injected volume. Calculations showed the excess energy over that required to operate the system was definitely produced at the surface. Total suspended and dissolved solids were very low indicating that HDR systems should operate without scaling or other major maintenance problems caused by the circulating fluid. Dissolved gas levels were so low that there were no gaseous emissions to the environment during normal, closed- loop operations.

Highlights:

a

a

a

0

a

a

0

a

a

a

Completed limited long-term testing at the Fenton Hill HDR test facility, amounting to about 8 months of flow operations including two long steady state flow segments of 112 days and 65 days.

Determined cause of pump failure which impeded flow testing in FY 92. Procured and demonstrated an economical and reliable pump to allow further testing.

Showed, by surface measurements and temperature logs at depth, that there was no decrease in the average temperature of fluid produced from the reservoir over the span of the long-term testing effort.

Showed, by multiple tracer tests, that additional hot rock within the reservoir was continually accessed and the volume of water stored in the reservoir increased as flow testing proceeded.

Showed that water consumption declined continuously to very low levels (7%) as reservoir pressurization and flow testing proceeded.

Showed that energy in excess of that required to operate the facility was definitely produced during steady-state flow testing. On a thermal basis the output energy exceeded the input energy by a factor of about 6.3.

Showed that the suspended and dissolved solids and the dissolved gases in the fluid circulating through the Fenton Hill HDR reservoir rapidly reached a steady-state level at very low concentrations.

Verified that no atmospheric emissions resulted from operation of the HDR facility under the standard closed-loop operating conditions.

Showed through seismic monitoring that only a few seismic events occurr? during the long-term flow testing period and that these were generally associated with periods of higher than normal production well pressures arising from system shut-ins.

Showed experimentally that the HDR reservoir impedance is concentrated in the direct vicinity of the production wellbore.

75

i


0 Verified that there is a broad pressure range over which backpressure may be applied to ‘the production wellbore without negatively impacting the production flow rate.

Demonstrated that cyclic operation of the HDR reservoir, entailing periodic short periods (a few minutes) of production shut-in, could increase overall system productivity.

Observed dramatic effect on reservoir impedance after a series of extended (multi-hour) shut-ins as part of a cyclic-operation experiment.

Demonstrated that the GEOCRACK model of fluid flow in fractured rock could validly represent observed flow in the reservoir over a range of injection and production pressures.

0 Continued industrial cooperation and technology transfer activities including the conclusion of the first formal Memorandum of Understanding with a private organization to work together toward implementing HDR technology. An important result of this effort was the first ever offer by a private geothermal company to extract energy from HDR resources in response to a power company’s Request for Proposals to supply electricity for commercial distribution.


Organizations

California Energy Commission Government of Japan Government of Germany

Geolectric Corporation .

Utilities

Extent of Interest

Cost-shared the research project.

In response to an RFP from Portland General Electric Power Co., Geolectric submitted an offer to supply 5h4W of electric power from HDR resources at Clearlake, California. Geolectric signed a memorandum of Agreement with the Los Alamos National Laboratory to jointly pursue the development of HDR.

In response to the Notice of Program Interest issued by the DOEiin September 1993, The Electric Power Research Institute submitted a letter endorsing the; development of a power- producing HDR facility and offering to participate financially if the project involved a member utility. Interest, to varying degrees, was expressed by Southern California Edison, Portland General Electric, Plains Electric, Niagara Mohawk, and Rochester Gas and Electric.

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Other Industry Independent power producers and resource companies wanting to expand into new energy areas including HDR. These include Ellicotville Energy, Frontier Technologies, Howell Gas Management, Earth Power, Honey Lake Industries, Geothermal Systems, and others.

Texaco and Bechtel also expressed interest as well as a number of equipment and drilling firms including Supreme Resources, Ormat, Geothermal Power Company, and Douglas Energy.


This research will yield an understanding of how to build, characterize and operate HDR energy production systems. It will not develop the ultimate HDR system, but it will carry the development of HDR to the stage where it will have demonstrated economic potential so that private concerns will see the economic benefits in investing in HDR power plants. The usual competitive and cost considerations will then lead the private sector to continually improve the technology making it more widely competitive and increasing its penetration of the energy market.

Tangible results will be two energy producing demonstration plants constructed jointly with private industry and operating at economically competitive costs.

Specifically, the work to date has resulted in the development of specialized drilling and logging equipment to drill and characterize wells in hard granitic rock. Technologies for fracturing hard rock in a controlled manner have been demonstrated. Tracer, geochemical, and seismic methods have been advanced to the state that HDR reservoirs can be well characterized in regards to size, dimensions, and many flow characteristics. Models have been constructed based on analytical and operational data to explain the behavior of reservoirs during pressurization and fluid circulation.

Recent flow testing has provided important information in regard to operation and maintenance of HDR plants as well as hard data on sustainable heat production, water consumption, net energy production, and environmental characteristics. This should set the stage for the development of an HDR facility designed to produce energy on a sustained basis for practical applications at competitive costs. That facility will, in turn, clearly demonstrate the commercial viability of HDR technology, thus leading to the construction of fully commercial HDR energy plants. All of these developments have moved HDR from the purely speculative stage of 20 years ago to a well-grounded, predictable technical state.

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~~~ ~~~ ~~

Expected Outcome

mr An understanding of how to characterize, build, and operate HDR production systems.

Demonstrate economic potential, so that the private sector will see the economic benefits of investing in HDR power plants.

An energy producing demonstration plant constructed jointly with industry and operating at economically competitive costs.


Presentation to the Geothermal Industry Advisory Panel, April 1993. Albuquerque, NM.

Transactions of the DOE Geothermal Program Review XI, April 1993. :Berkeley, CA.

Transactions of the EPRI HDR Workshop, January 1993. Philadelphia, PA.

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FY93 ANNUAL PROGRESS REPORT RESERVOIR ENGINEERING APPLICATIONS

GEYSERS COOPERATION

Background

Since the late 1980’s operators and utilities at The Geysers became aware that field production was declining. At the same time, the fluid chemistry was also changing in some portions of the field. Generation at The Geysers has declined to about 60% of the original installed capacity. This research will try to find adequate solutions to the problems experienced at The Geysers geothermal field.

Objectives

To improve understanding offractures, veins, breccias and the felsite as controls of permeability and reservoir storage.

To develop geochemical models that can be used to describe the evolution of the system and the location of corrosive fluids.

To demonstrate the use of high-quality seismic data to delineate fracture patterns and fluid saturation in the reservoir.

To determine the nature and extent of adsorption on field pejormance.

b

b

b

b To develop new tracers.

b

b To mitigate corrosion.

To test and evaluate injection practices, and extend the commercial lifetime of the field.

Approach

Research types and industry needs are closely coordinated and evaluated. Industry reviews all research proposals and suggests its priorities to DOE. Industry also provides much of the data used in the research program. Cooperation between researchers and appropriate industry personnel is maintained throughout the research. Periodic meetings are held to update industry on research progress and seek new direction.

Reservoir Engineering

Research Status, and Findings I

Field evidence and numerical results show a pronounced sensitivity of injection derived steam (IDS) recovery to the rate of injection, the relative degree of depletion at the time injection started (reservoir superheat), and permeability. Historical injection was’ reviewed and numerically modeled in two separate portions of The Geysers reservoir with different initial reservoir conditions. Evaluation of an optimum injection rate for a new injection well in the Unit 13 area of the Southeast Geysers is underway.

79

Organizations

Calpine Corporation Central California Power Agency No. 1

Northern California power Agency UNOCAL


A set of design and reservoir parameters influencing the recovery of injection derived steam (IDS) will become available. Operational guidelines to implement successful injection projects, for efficient use of available water and successful heat mining at The Geysers, will be established. The reservoir physics involved in depletion and re-injection processes will be understood. This allows one to picture the role of adsorbed water and optimize reservoir development and management strategies. Further, new algorithms will be included in routine reservoir simulation tools. Application of results to steamfield operations at The Geysers will enable better utilization of the limited condensate available for injection, as well as for any future injection or water augmentation projects.

Extent of Interest

Contributed data and expressed interest in steamfield operations.

Expressed interest in steamfield operations. I


Faulder, D. D., 1992. "Model Study of Historical Injection in the Southeast Geysers," Proceedings of the 17th Workshop on Geothermal Reservoir Engineering. Stanford University, Stanford, CA.

Shook, G. M., 1992. "Parametric Study of Reservoir Properties and Their Effect on Energy Recovery. " Proc. 17th Workshop on Geothermal Reservoir Engineering. Stanford University, Stanford, CA.

Faulder, D. D., 1993. "Southeast Geysers Injection and Reservoir Model Study." DOE Geothermal Program Review XI, San Francisco.

Hornbrook, J. W. and D. D. Faulder, 1993. "Parametric Analysis of Factors Affecting Injection and Production in Geothermal Reservoirs. " Proc. 18th Workshop on Geothermal Reservoir Engineering. Stanford University, Stanford, CA.

Shook, G. M., 1993. "Numerical Investigations into the Formation of a 'High Temperature Reservoir'." Proc. 18th Workshop of Geothermal Reservoir Engineering. Stanford University, Stanford, CA.

I

Shook, G. M., 1993. Generalization of Vapor Pressure Lowering Effects in an Existing Geothermal Simulator. EGG-EP-10787, June, 16 pp.

i

80

FY93 PROGRESS REPORT RESERVOIR ENGINEERING APPLICATIONS

Stanford Geothermal Program Industrial Affiliate Companies (PG&E, UNOCAL, Calpine, and NCPA.)

0

Contributed funding for the research.

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Adsorption and


Stanford researchers conducted an experimental and theoretical investigation of steam adsorption, and a theoretical investigation into the movement of tritium tracers at The Geysers. The adsorption area resulted in several significant findings. Researchers performed several sets of adsorption measurements on geothermal rocks using both equilibrium and transient experiments, and found the results to be in agreement. This allowed confidence in the values measured, and provided firm estimates to be used by industry. The theoretical study also resulted in qualitative confirmation of the experimental observations. A report and three technical papers summarized these results. In the tritium tracer study, researchers developed a mathematical model to compute the displacement of fluids and demonstrated agreement with complete simulation. This provides a model by whi,ch the importance of the individual effects can be isolated and evaluated. A paper and a report on these results are in preparation.


I Organizations I Extent of Interest I


Near term applications are mainly associated with forecasting the near-future of the Geysers geothermal field and determining optimum ways to improve its performance. Measuring adsorption and understanding its properties allows more realistic calculation of the field's drawdown, and enables better analysis of the likely effects of injection (such as from the Lake County injection pipeline).


Qi, M. "Estimation of Adsorption Parameters from Experimental Data." SGP Technical Report, May 1993.

Shang, S.B., Home, R.N., and Ramey, H.J., Jr., Jan. 1993. "Experimental Study of Water Adsorption on Geysers Reservoir Rocks." Proceedings of the 18th Stanford Workshop on Geothermal Reservoir Engineering, Stanford, CA.

Correa, A., and Ramey, H.J., Jr., "Theoretical Investigation of Adsorption in Porous Media." Paper submitted for publication.

I

81

FY93 ANNUAL PROGRESS REPORT RESERVOIR ENGINEERXNG APPLICATIONS

Corrosion Mitigation at The Geysers


Researchers performed field evaluations of prototype and full-scale corrosion-resistant materials. These ongoing tests are being conducted at the following locations: The Northern California Power Agency (NCPA) facility in Middletown, CA, and the Central California Power Agency (CCPA) Facility in Cloverdale, CA. In addition, plans for cost-shared test programs with PG&E to select corrosion protective coatings for turbine rotors and dry cooling towers were made. Results to date are summarized below.

A. NCPA Field Tests

The first visual inspection of two polymer cement (PC) lined 12-inch diameter pipe tees being tested at The Geysers as a cooperative cost-shared effort between BNL and the Northern California Power Agency (NCPA) was completed in April, 1993. One section was exposed for 13 months, the second for 12 months, both at a steam flow rate of 30,000 Ibhr, 120 psi pressure,.and a temperature of 170°C. Observations noted are listed below.

0 After 13 months in service, the non-reinforced PC showed no wear or chemical deterioration of the liner except at the upstream end where some erosion at the edge of the 5/16-in. thick liner occurred. This probably resulted from the step change in the diameter of the pipeline at this point which caused the direct impingement of the high velocity steam onto the unsupported edge of the liner.

0 A network of fine surface cracks in the PC that formed during fabrication as a result of excessive shrinkage did not appear to enlarge as a result of field exposure or to promote disbondment.

0 Similar observations were noted for the second tee which contained 0.23% graphite fibers by weight of the PC as a means for reducing shrinkage cracking. One small (- 2 to 3 square-inch) area where disbondment of the PC from the metal occurred was detected. A defect in the liner was originally present at this point probably due to air entrapment during casting, and a patch had been applied. The clean, bright surface of the steel after the 12 month test would indicate that the disbondment occurred late in the test cycle.

0 Based upon the excellent condition of the tees, both were reinstalled for continued exposure. Trouble-free operation continued throughout the rest of the year. %e next inspection will occur in April, 1994.

I

B. CCPA Field Tests

In this effort, two polyphenylene sulfide coated well casing spool sections, 8-inch i.d. x 12-inch long, used to inject NaOH solutions into chlorine-containing steam were in service for approximately 12 months, but not always under the caustic injection condition. Typically, 0.5-in. wall steel casing will corrode through within 14 days when exposed to the low pH (-2), high temperature (- 170°C) condensate produced when NaOH injection is used. The status of the tw;o BNL-supplied sections, both of which have provided trouble-free service, is as follows: (1) One section was placed in a well on October 8, 1992 operating at 145 psi, 176°C and a steam flow rate of 54,000 Ibhr. The chloride content

82

. . . . . - -. .. . . . . . .. .

Organizations

Central California Power Agency (CCPA) Northern California Power Agency (NCPA) Army Research M i c e Pacific Gas and Electric Co. (PG&E)

UNOCAL

Long Island Lighting Company

Gas Research Institute

P

P

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u

b

Q

Extent of Interest

Cost-shared testing collaborator and potential user of technology.

Current user of technology.

Potential user of technology for air preheaters in oil-fired electric generation.

Cost-shared testing and potential user of technology in condensing heat exchangers.


in the steam is 10 ppm. Conversion to NaOH injection at the bottom of the casing string was made on October 27, 1992 but the test spool was left in place. Operation has been trouble-free since. (2) A second section is in a well operating at essentially the same conditions except the steam flow is 70,000 lbhr. This test commenced on November 2, 1992. During that 11 month period, caustic injection into the section was conducted for 3 months. Downhole injection was used during the other months. Again, no leakage problems have been encountered. Bossections were scheduled for visual examination in late November, 1993.

-25, d y f , 5p&t k

~ ~~ _______

Consolidated Edison Co. of New York

C. Lab oratorv Testing

Potential user of technology in steam district heating systems.

Screening tests on high temperature organic and inorganic polymer coatings being conducted to select materials for planned FY 1994 dry cooling tower and turbine rotor evaluations were initiated. Salt spray evaluations commenced in July, and testing in flue gas condensate containing H2S0, was started in August.


Potential user of technology for brine pipeline I coatings. Magma Power Company


Low cost corrosion pfotective coatings for well casing, turbine blades, turbine rotors, steam and brine collection piping, andildry cooling tower components will become available for commercial use.

$ I

I !

Publications and Presentations I

Webster, R.P., Kukacka, L.E., and Reams, W., Sept. 1992. Development of polymer concrete liners and coatings for use in geothermal applications. BNL 48002. American Concrete Institute Special Publication "Recent Innovations in Polymer Concrete Technology", (in press).

83


Organizations

UNOCAL Northern California Power Agency Central California Power Agency Calpine Corporation

Pacific Gas and Electric Co.

Kukacka, L.E., 1993. Materials for geothermal applications. m. Geothermal Program Review XI, Berkeley, CA, Apr. 27-28, 1993, DOE CONF/930484, Washington, 133-140.

Extent of Interest

Contributed data and field support. Expressed high interest in results of this research.

Moderate interest in results of this research.

Microearthquake Monitoring at The Geysers


Research results indicate that microearthquake (MEQ) data can be used to:infer the flow of injected liquid within the vapordominated reservoir. Results of the imaging indicate that the seismic attenuation and Vp/Vs ratio could possibly be used to estimate reservoir fluid saturation.



Improved and cost-effective microearthquake (MEQ) field monitoring and data interpretation techniques will be available to industry for use as a reservoir management tools to track the movement of injectate in the subsurface and estimate the liquid saturation in the reservoir.


Peterson, J.E., Jr., Majer, E.L., Romero, A.E., Jr., and McEvilly, T.V., 1992. A search for production-induced changes in seismicity or velocities at the northwest Geysers geothermal field, California. Poster presentation, American Geophysical Union 1992 Fall Meeting, December 7-1 1, San Francisco, CA. \

Romero, A.E., Jr., Vasco, D.W., and Majer, E.L., 1992. Non-linear inversion for velocity structure at the northwest Geysers. Poster presentation, American Geophysical Union 1992 Fall Meeting, December 7-1 1, San Francisco, CAt

Majer, E.L. et al., 1993. Seismic monitoring at The Geysers. Proceedings Geothermal Program Review XI, April 27-28, 1993, Berkeley, CA., Conf./-930484, pp. 55-64.

84

FY93 ANNUAL PROGRESS REPORT RESmvorrt ENGINEERING APPLICATIONS

~~

Calpine Corporation Northern California Power Agency Central California Power Agency

UNOCAL Pacific Gas and Electric Co.

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Gas and Isotope Geochemistry of Geysers Steam

- ~ ~ ~~

Provided field data and expressed high interest in the research.



LBL developed a model for the origin of distinct (but connected) reservoirs in the NW and SE Geysers based on differences in depth, access to recharge water and rock types.


Organizations I Extent of Interest I

.


LBL gas geochemistry studies will provide methods to interpret gas and isotope geochemistry data to develop optimal reservoir managements plans during different exploitation phases of a geothermal resource.


Truesdell, A.H., 1993. Gas geochemistry of The Geysers geothermal field. Proceedings Geothermal Program Review XI, April 27-28, 1993, Berkeley, CA, Conf/-930484, pp. 85-90.

Truesdell, A.H., Enedy, S.L., and Smith, J.L., 1993. Geochemical studies of reservoir processes in the NCPA field of The Geysers. Proceedings 18th Workshop on Geothermal Reservoir Engineering, January

I 26-28, 1993, Stanford, CA (in press).

Truesdell, A.H., Walters, M., Kennedy, M., and Lippmann, M., 1993. An integrated model for the origin of The Geysers geothermal field. Geothermd Resources Council Trans., Vol. 17, pp. 273-280.

! I

85


Organizations

~ ~~

Lake County Effluent Pipeline


Lake county has initiated preliminary design of a pipeline that will supply additional sewage water for

Extent of Interest

injection at the southeast Geysers. An environmental impact statement is also being prepared.


Calpine Corporation Northern California Power Agency Bureau of Land Management California Energy Commission Lake County Government

All geothermal operators at The Geysers and others using injection to maintain field Derformance.

Cost-shared in the project.

Expressed interest in the research.


This project will supply a pipeline that provides sewage water that can be injected into the southeast Geysers geothermal field. The injection of additional water is expected to contribute to a build-up or to a lesser decline in reservoir pressure.


Project sponsors have held several workshops explaining the project to the public.

J

86

FY93 ANNUAL PRO.GRESS REPORT RESERVOIR ENGINEERING APPLICATIONS 1 .

4 fir

Geology and MagmatidHydrothermaI History of the Hypabyssal Felsite Beneath The Geysers Steam field


1. Three major intrusive phases have been identified to date in The Geysers felsite -- Biotite- orthopyroxene granite; biotite rhyolite porphyry; and orthopyroxene-homblende-biotite-granodiorite (see Figure 16). A fourth rock type is geochemically a low-silica granite, but appears to be a hybrid representing assimilation of the orthopyroxene granite by the younger granodiorite.

1:

Approximate outer limit of The Geysers steam field

NEGU-8' 0

Area of this map

-38" 45'

4

Wmi 1 2 3 4 5km

'45'

Felsite-Study Wells 0 Cuttings only + Cuttings and core

ri* \

= Dikes in Franciscan metascdimentary mcks

Figure 16. Map of The Geyser steam field, showing locations of wells penetrating the concealed "felsite" intrusive complex and utilied for this investigation.

87

FY93 A N N L l a PROGRESS REPORT RESERVOIR JI~GJNEERING APPLICATIONS

2. The Geysers granite and rhyolite porphyry have been dated utiliiing 40ArP9Ar methods (G.B. Dalrymple, USGS) as at least 1.3-1.4 m.y. old -- the rocks are too/thermally disturbed to yield a more precise age. With these minimum ages, however, they are cleaily not the intrusive equivalents of the immediately overlying Cobb Mountain rhyolites of the Clear Lake volcanic field (about 1.1 M.Y.1.

t

Approximate outer limit of The Geysers steam field

Extent of stem reservoir at elevation (-)3000 fl

I

I

-38" 45'

1 2 3 , 4 5km

0 Candidate geothermal wells for The Geysers coring project (surface locations)

Top-of-felsite ,5. contour, ft x I$

@sea level

\: .Cob< Mountain

xtent of felsite at

Felsite and s t d i e l d configurations from Unocal, d al., 1992

Figure 17. Locations of well SB-15 for The Geysers coring project relative to the steam field and coaxial, underlying felsite pluton.

3. The Geysers granodiorite has the same chemical composition and virtually the identical aArPAr age as the overlying Cobb Mountain dacite of the Clear Lake volcanic field. Thus, these units are good candidates as intrusive-extrusive equivalents (see Figure 17). Since the Cobb Mountain dacite rests on the paleosurface at the time of intrusion/extrusion, the depth of granodioritic magma emplacement is constrained. That depth is surprising shallow, about 3 km.

88


I Organizations Extent of Interest I

Calpine Corporation Russian River Energy Company Santa Fe Geothermal UNOCAL

Supplied cuttings, cores, and miscellaneous supporting downhole data for the felsite project.

' All except Russian River produce extensively from the pluton, and new information which

, enables them maximize yield from this igneous body would be of great interest.

4.

5.

6.

There are two zones of intense ,tq;rmaline & ferroaxinite enrichment in the felsite and overlying contact-metamorphic hornfels. One zone, in the northwest Geysers, boasts enrichment in these two minerals up to at least 20 wt% through 60-m intervals. This northwestern zone coincides with the portion of the geothermal field which has produced corrosive, low-pH steam. A second zone occurs in the central Geysers, above the shallowest (relative to the current erosional surface) felsite. The central zone persists downward up to 1 km into the felsite, but attenuates with depth, suggesting that the anomaly is related to exsolution of boron-rich magmatic fluids at the top of the penetrated pluton (rather than to a deeper pluton beyond the reach of current geothermal wells).

Tourmaline is clearly a magmatic-hydrothermal mineral at The Geysers. It is closely associated with the felsite, diminishing dramatically with distance from the pluton. It is also invariably associated with high-temperature ( > 350°C, characteristically), highly saline fluid inclusions, commonly with halite daughter minerals. On the other hand, ferroaxinite is associated with less saline, lower- temperature fluid inclusions; it also replaces tourmaline and seems to represent later-stage incursion of more dilute hydrothermal fluids into the Geysers system. Enrichments of borosilicates are commonly, though not invariably, associated with steam entries in Geysers geothermal wells.

Miarolitic cavities in shallow felsites provide abundant steam-reservoir porosity. It seems likely that these cavities play the same role as carbonatedissolution voids in the overlying Franciscan- metagraywacke-hosted portion of the field - they store the field's liquid water reserves.

-

In view of the discovery of the east Geysers granodiorite in a few wells at the eastern edge of the field, and the young age of this pluton and its significance in establishing a depth of emplacement for at least part of the felsite, researchers have obtained felsite cuttings from several additional east Geysers wells. Researchers have also obtained several enigmatic "intrusive" rock samples from outcrop within the steam field, and will study these to determine their affiliation (if any) with the deeper felsite already characterized.


89

FY93 ANNUAL PROCRESS REPORT RESERVOIR ENGINEERING APPLICATIONS

Patterns of hydrothermal brecciation and alteration as well as veinhreccia mineralization in the felsite and overlying hornfels conceivably will be of use in targeting more productive sectors of the felsite-hosted steam reservoir, and in predicting approach to individual steam entries. Since rniarolitic cavities seem to be significant fluid-storage sites in the upper levels of the known felsite, discovery of a deeper pluton with these high-level voids beneath currently drilled depths has potential to increase the field's reserves. Such a hypothetical pluton could be signalled by higher-level dikes, concentrations of hydrothermal breccias, or downward increases in the intensity of hydrothermal alteration and vein mineralization.

Each of these objectives will be addressed by completing a set of detailed plan maps and cross-sections showing lithology, alteration, mineralization, and degree of brecciation (to the extent this can be determined) in the felsite at progressively deeper levels; and these features, plus metamorphic grade and mineralogy in the overlying hornfelsic halo.


Hulen, J.B., and Nielson, D.L., 1993. Geology and hydrothermal alteration of felsic plutonic rocks at The Geysers steam field, California (abs.) Geothermal reservoir technology research program, abstracts of selected research project (M.J. Reed, ed.). U.S. Department of Energy, Geothermal Division, Report DOE/CE-0397, p. 93-97.

Hulen, J.B., and Nielson, D.L., 1993. Interim report on geology of The Geysers felsite, northwestern California. Geothermal Resources Council, Transactions, v. 17, p. 249-258.

Hulen, J.B., and Walters, M.A., 1993, The Geysers felsite and associated geothermal systems, alteration, mineralization, and hydrocarbon occurrences The Geysers geothermal 'area and the McLaughlin gold deposit, California (J. Rytuba, 4.). Society of Economic Geologists, Fieldtrip Guidebook, 12 p. 141- 152.

90

FY93 ANNUAL PROGRESS REPORT RJBERVOIR ENGINEERING APPLJCATXONS u

0

Geysers GeocbemistrF '?: I ;,


In FY93, Unocal provided UURI with more than 550 whole-rock oxygen isotope data from The Geysers. UURI researchers are collaborating with Unocq to interpret the data and incorporate it into an evolutionary model of the geothermal system. The isotope data provides independent evidence of a large hydrothermal system that developed in response to emplacement of the granitic intrusion that underlies the geothermal field (see Figures 18 and 19). The major feature of the isotopic data is the presence of a pronounced elongated isotopic low located near the geographic center of the field. This low is interpreted as representing a structurally controlled vent area for the hydrothermal fluids. Variations in the isotopic compositions of the rocks around the low appear to be the result of the temperature gradients developed around the earliest and most extensive of the intrusive phases within the pluton.

Interpretation of the isotopic data is not yet complete. During FY94, researchers will complete evaluating the data and integrate it with the results of fluid inclusion and mineralogic investigations that have been conducted. A preliminary paper on the data will be presented at the 19th Workshop on Geothermal Reservoir Engineering at Stanford University.

Calcite

a

Q B B

Figure 18. Collapse of the initial liquiddominate regime during the second stage in the evolution of the Geysers geothermal system. During this stage, fluid movement was dominantly toward the intrusion as indicated by the black arrows.

Gi I 91


Organizations Extent of Interest

UNOCAL

Calpine Corp. and Russian River Energy Corp.

NED0 (National Energy Development Organization of Japan)

Japanese Geological Survey Collaborative studies.

ENEL (Italian National Electrical Utility)

Provided isotopic data and interested in cost- shared studies.

Cost-shared studies.

Application of models to Japanese systems.

L

Application of models to Larderello.

I

0 0 0 0

Condensat ion r I High- Temperature Reservoir Reservoir

Figure 19. Initial development of the present vapordominated regime during the third stage in the evolution of The Geysers. Circles show boiling in upper part of system while black arrows show downward movement of acid condensate.


I

FY93 ANNUAL PROGRESS m R T RESERVOIR ENGINEERING APPLICATIONS

Domestic and international geothermal industry and electrical utilities (UNOCAL, California Energy Co., Russian River, Calpine, NCPA, PG&E. and CFE)

V%d ;+ Vapor-Phase Tracer Development 4 A !


Inquiries on tracer usage and choices, cost- shared tracer tests, short courses.

UURI researchers finalized plans for a tracer test at The Geysers. The test will be done in conjunction with Unocal, PG&E, NCPA, and Calpine to evaluate injection responses from the Unocal section of the southeast Geysers. It will be performed on a Unocal injection well converted from a production well. UURI’s portion of the test consists of providing a proven vapor-phase tracer, R-13, and to provide other less expensive tracers to test against R-13. SF, will be used for comparison with R-13. / Unocal will simultaneously perform a tritium tracer test while UURI researchers will use isopropanol, a more soluble tracer, and compare its performance against that of tritium.

~

DOE Waste Isolation

Geothermal Resources Council

United Nations

International Atomic Energy Agency

ENEL (Italian national electrical utility)

Researchers also began development of two-phase tracers for use at The Geysers. Alcohols were identified as a class of compounds having significant solubility in both liquid and steam phases and appear to be relatively stable at geothermal temperatures. To date researchers have tested ethanoldistilled water solutions in a pressurized autoclave at temperatures of 220°, 240°, and 280°C for up to four weeks. No significant reduction in the ethanol concentration and no-decay products were detected in these experiments. Objectives for the ethanol tests are to produce some decay, so that the reaction rate can be quantified. In order to quantify reactions the solutions will be heated for longer time periods and in more complex solutions. Researchers also plan to test other alcohols such as isopropanol, which has a better detection limit. Isopropanol, rather than ethanol, will be used because of its lower detection limit.

Tracer data to analyze the hydrology of waste repositories.

Short courses on geothermal tracers for the geothermal industry.

Short courses on geothermal tracers for developing countries.

Tracer tests in developing countries.

Inquiries and paid lectures on tracer usage and choices; use at Larderello.

Two candidate tracer compounds were field tested at The Geysers. One of these compounds proved suitable for tracing injected water, but is unfortunately being phased out of production according to the Montreal Protocol. Additional field testing of two strong tracer candidates is expected during the next fiscal year. More tracers need to be found and quantitative data on their stability and solubility need to be developed. The goal is to identify at least 6 viable tracer species of varying solubilities.


I Organizations Extent of Interest

93

FY93 ANNUAL PROGRESS REPORT RESERVOIR E~GINEERING APPLICATIONS


This research will ultimately yield a variety of tracers (minimum of 6): suitable for conditions at The Geysers. Some of these tracers will fractionate into the liquid phase in the reservoir so that they can be used to examine the rate and direction of boiling of the liquid injection plume in the reservoir.

The tracers developed by UURI are already being used by industry. By 1995, the geothermal industry will be using the additional tracers now under development. I

Expected Outcomes from the Geysers Cooperation Project

Improved methods of corrosion control could increase the usefur thermal energy'by several percent in some areas of thefleld.

I

s Improved injection practices, including operation of the Lake County sewage pipeline, have been estimated to provide up to 7percent more energy production.

Improved understanding of the reservoir translated into better operating practices will lower the cost of production and increase the reserves.

94

FY93 ANNUAL PROGRESS REPORT RESERVOIR ENGJNEERING APPLICATIONS

Organizations

California Energy Company U.S. Navy

Calpine Corporation Central California Power Agency Northern California Power Agency Pacific Gas and Electric

Calpine Corporation Northern California Power Agency Pacific Gas and Electric UNOCAL

Extent of Interest

Cost-shared studies at the Cos0 geothermal field.

Cost-shared gas studies at The Geysers.

Cost-shared injection studies at The Geysers.

Implications for Future Geothermal Development -

The seismic data interpretation project at Coso, conducted by Duke University researchers, will show the utility and develop improved methods of seismic structural interpretation in a structurally complex area similar to that found in many geothermal systems. The study of fracture geometry by the University of North Carolina will develop methods for interpreting microseismic data that will allow the user to determine fracture locations and density. This information is very important in siting wells of high productivity.

-

The Geysers injection study will increase understanding of injection in a vapor dominated reservoir and provide information on tracer suitability to the industry.

~~

Expected Outcome

= Improved reservoir management tools resulting from the immediate transfer of completed research to industry.


Papers are not scheduled until FY 1994. The participating GTO members have been provided periodic updates throughout the projects.

96

FY93 ANNUAL PROGRESS REPORT RESERVOIR Eh'GmTEm'C APPLICATIONS

Objectives

w To undertake industry suggested research thar has a high probabiliry of yielding benefits to the industry in the short term.

GEOTHERMAL TECHNOLOGY ORGANIZATION

Background

Numerous technical problems need to be solved by the geothermal industry. This project is a formal agreement between the U.S. geothermal industry, represented by the Geothermal Technology Organization and the Department of Energy to cost-share research proposed by the industry.

Approach I

The geothermal industry, researchers, and DOE propose research projects to the GTO and'GTO members decide whether to participate in projects on a case b y case basis. After two or more GTO members agree to fund a project, the proposal is sent to DOE for approval. On approval by GTO members and DOE, the Idaho National Engineering Laboratory conducts the proposed research or subcontracts the research to an appropriate research organization.


Two research projects on the Cos0 geothermal system were active during FY 1993. Researchers used using seismic data collected during exploration and development to: 1) more accurately determine the structure of the field, and 2) determine fracture paMerns and the crack network geometry of the system. Researchers at Duke University reinterpreted geophysical data from Cos0 to redefine the structure of this important geothermal field. Improved velocity profiles were used in the second Cos0 project to characterize fracture density and location. Reports from both these studies will be available to the GTO sponsors in early 1994. Publications were presented in December 1993 at the American Geophysical Union fall meeting.

Two projects at The Geysers geothermal field werc initiated near the end of the fiscal year. One project is an important long-term test of injection in a portion of the field. This project will also test several chemicals that laboratory testing has indicated may be suitable as tracers in vapor dominated systems. In the second project, gases associated with the steam at The Geysers will be studied to improve prediction of their change over time.

GTO members are discussing expansion of the sekmic work at Coso. There is also some interest in applying the methods at The Geysers.

95

Geothermal energy conversion costs are capital intensive. Operation and maintenance (o&M) costs can also be high depending on the chemical environment. Low-to-moderate temperature geothennal resources are More widespread than high-temperature resources and contain less aggressive fluid&. However, the lower temperatures dictate the need for high pevormance binary cycles to enable cost-eflective electricity generation. The aggressive chemistry encountered at some high temperahre resources dictates the need for scale and corrosion resistant materials for heat exchanger applications, energy conversion processes, and well cementing operatiom. Toxic elements found in geothermal sludges also need to be treated prior to injection or su?fiue disposal. Addressing these issues will reduce the cost of power from geothermal resources, and is the focus of the Conversion Technology Task.

97

. . .. . . .

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FY93 PROGRESS REPORT CONVERSION TECHNOLOGY

HEAT CYCLE RESEARCH

Background

The development of geothermal energy for the productdn of electrical power has to date focused primarily upon the higher temperature hydrothermal resources. Relative to conventional fossil-fuel power plants, geothermal is a low-grade (temperature) resource which must be produced in significant quantities to generate a given level of power.

As the temperature of the resource drops, a number of factors contribute to a higher capital cost for the energy conversion system, or power plant. These include a decrease in the optimum cycle efficiencies and an increase in the heat rejected, larger heat exchangers resulting from smaller temperature differences, and larger piping and turbines required for larger fluid flow rates and lower fluid (vapor) densities. In addition, as the temperature of the resource decreases the costs associated with producing and disposing of more of the geothermal fluid also increase. As a result of these higher plant and field costs, the development of the moderate temperature (100" to 150°C) hydrothermal resources have been slower, even though the geothermal fluids are typically more benign than the higher temperature fluids. These moderate temperature resources however, are more abundant than those at the higher temperatures, offering a significantly higher potential contribution to the nation's energy needs.

In order to realize the potential of these moderate temperature resources, technology must be developed which will result in lower costs for producing the electrical power. While other research areas address technology improvements and cost reductions associated with the supply and disposal of the geothermal fluid, in this research area, investigators are examining improvements to the energy conversion systems used to generate the electrical power. The goal of this research effort is to derive the technology base for thermodynamically efficient systems that result in lower cost electricity. For the liquiddominated, moderate-temperature resources, investigators have shown that the binary cycle technology is more efficient than the flash-steam technology in converting the energy contained in the geothermal resource to electrical power, and should result in lower costs of power.

These binary cycles are the primary focus of the current project investigations. The technologies currently being evaluated have the potential for improvements of up to 28% in the geothermal fluid utilization, and are approaching the maximum practical limits of performance that could be achieved by an idealized power cycle. By maximizing the performance of these cycles, investigators have shown that the amount of geothermal fluid is significantly reduced, and the associated savings which result are greater than any additional cost associated with the energy conversion system. In addition to lower the cost of producing the electrical power, these technologies have the added benefit of conserving the energy source.

These efforts will ultimately lead to an increased utilization of the moderate temperature hydrothermal resources, and a larger contribution by geothermal energy to the nation's energy needs.

98

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FY93 ANNU& PROGRESS REPORT CONVERSION TECHNOLOGY

Objectives

b To increase the net geothermal fluid utiluation (net power produced per unit mass offluid) of binary power cycles by 20 percent.

b To increase the net geothennal fluid utilization of binary power cycles an additional 8 percent through the utilization of supersaturated turbine expansions.

(Pegoormmcc improvements are relative to the projected peflormance of a Heber-type binary power plant.)

Approach

The following defines the overall approach used by the project in attaining its stated objectives:

Concepts with the potential for meeting the stated objectives are identified, analytically evaluated, and compared to a reference plant to determine the relative impact on performance and cost of power. A determination is then made as to whether the technology required is available and adequate to incorporate those concepts with potentially significant performance/cost gains.

If determined necessary, field investigations are initiated to validate and/or develop the necessary technology base.

Data generated in field investigations are used to evaluate the adequacy of existing design tools and property codes, as well as validate the assumptions made in deriving the performance projections. Results are made available to the industry through papers, presentations, and reports. Final reports are prepared defining the performance improvements and cost reductions, as well as the technology required to incorporate the concept(s) into a commercial application.

The final step in achieving the stated objectives is to assist with the assimilation of the technology into industry.


During FY-1993, researchers initiated investigations at the Heat Cycle Research Facility to examine the condensation behavior of supersaturated vapor expansions. The objective of these investigation was to determine the extent to which condensate formed when the working fluid entered and exited the equilibrium two-phase region during the expansion process, and to use a Raleigh-scattering technique to size the droplets which did form. It had been analytically predicted that condensate may not form until an isentropic expansion process between the inlet and exhaust pressures remained completely within the two-phase region. It is the concern relative to condensate formation and its potential damage to turbine internals, which leads plant operators to operate their turbines in a conservative regime, well outside of the two-phase region.

To conduct these investigations,-a two-dimensional expansion nozzle was installed in the working fluid system at the HCRF. The n o d e was utilized to simulate isentropic turbine expansions of interest. A window along the length of the nozzle allows the expansion process to be monitored. Pressure taps are also located along the length of the nozzle providing a pressure profile of the expansion process. A laser-

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m93 ANNUAL PROGRESS REPORT CONVERSION ~ C H N O L O G Y

based detection system was installed to identify when and where conhensate was present in the expansion process. Any droplets forming during the expansion process scattered the laser; the scattered light was detected and measured providing investigators an indication of where the condensate was forming. These scattered light measurements were also used to attempt to size the droplets using a Raleigh-scattering technique.

1 ,

The nozzle investigations revealed the following relative to the condensation behavior of the supersaturated expansions:

Under certain nozzle inlet conditions, a metastable vapor could be maintained during isentropic expansions when the expansion path, if at equilibrium, would pass within the two phase region. The data indicate that moisture levels of 6% to 7% (at equilibrium conditions) can be maintained before condensate forms.

The investigations also showed that once condensate formed, it tended to re-evaporate as the expansion continued. This had been predicted in the early analytical studies which provided the basis for these investigations.

The initial attempts to size the droplets with the laser system were inconclusive. The measurement process is complicated by the variation in the fluid index of refraction (with density changes) as it is expanded in the nozzle.

Condensate tended to first form at the throat of the nozzle which was generally at a pressure corresponding to the highest entropy on the working fluid dew point curve; it was originally postulated that the condensate would form at pressures nearer the critical point.

Subsequent conversations with representatives from industry suggest the performance gains possible from utilizing the metastable, Supersaturated expansions could be higher than projected, even though the metastable state could not be maintained to the same degree of moisture as initially projected (7% vs 12%). This additional performance would result because utilities tend to operate the turbines in a more conservative mode than initially assumed (more superheat in the vapor entering the turbine).

Based upon interest expressed by industry, these investigations were expanded to include the testing of a turbine (axial flow, impulse unit) to determine what effect these expansions would have on the turbine performance. This work will be accomplished during FY 1994.

The investigations conducted to date have validated the assumptions used in making the performance projections for the 20% improvement in geothermal fluid utilization that will be realized by using the concepts defined by this research. While inadequacies have been defined in the technology base required to utilize these advanced cycles, the results of these research efforts can be used to augment existing technology to adequately design a commercial energy conversion system which could utilize these concepts and realized the stated 20% performance improvement.

The field investigations for the supercritical cycle testing and the accompanying data evaluation have been completed and a final report has been drafted and prepared for peer review. With the publication of the final report in FY 1994, the technology for achieving the 20% improvement in performance will be defined and presented to the industry.

Field investigations initiated in FY 1993 have shown that it is technically feasible to achieve the final 8% projected improvement in performance by allowing the supersaturated turbine expansions. During

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FY93 ANNUAL PROGRESS REPORT CONVERSION TECHNOLOGY

Organizations

Heat Transfer Research Inc.

FY 1994 field investigations will be completed to define the impact of these metastable supersaturated expansions on the performance of a turbine. With the completion of these investigations, the project will define the degree to which the metastable vapor expansion can be maintained without an adverse performance penalty, and show that the projected performance gains are possible.

Extent of Interest

Data collected during the supercritical cycle investigations, and the experience gained in using HTRI’s design codes is of interest to HTRI as it continually attempts to develop and improve its design methods. HTRI’s design codes are widely used by heat exchanger manufacturers, utilities, and engineering firms to specify, size, and design heat exchangers.

The remaining task will be to assure the technology is readily available to industry, and that adequate steps are taken to encourage industrial use of the technology. This effort is in progress, particularly with regard to the metastable supersaturated turbine expansions.

As a result of the interest expressed by the geothermal industry in the supersaturated turbine expansions, these investigations were expanded to include the testing of one or more turbines to examine the impact of these metastable expansions on the performance of the turbine. In order to accommodate industry interest in this activity, the project redirected the funding established for the closeout of the HCRF in FY 1993 to conduct the first phase of this extended testing; examining the impact of these expansions on an axial-flow, impulse turbine. The funding in the budget for the closeout was used to obtain the use of an impulse turbine and install the unit at the HCRF. This phase of investigations was initiated at the HCRF in FY 1993 with the facility modifications and turbine installation; the field testing will be started and completed in FY 1994, and the results reported.

The program objectives to date have been focused on the results of the research being conducted. Given that the research has identified power cycles which will operate near optimum performance, and validated the technology to achieve these performance levels, the program objectives should begin to reflect more emphasis on the commercialization of the technology.


UtilitiesPlant Operators (Mission Energy) Reduced costs of producing power and extended resource lifetimes are of major interest to utilities and other power producers.

Mission Energy expressed interest in the supersaturated turbine expansion investigations for possible application in an existing binary power plant. Mission also expressed some interest in the supercritical cycle technology.

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Turbine Manufacturers (Barber-Nichols)

Engineering Firms (Ben Holt Co.and Barber- Nichols)

Additional insights into supersaturated turbine expansions and information to encourage the removal of conservative constraints placed upon the design and operation of turbines. Barber- Nichols’ interest is in the impact of these expansions on an impulse turbine. Barber- Nichols has loaned an axial-flow impulse turbine for conducting tests to establish the impact on performance.

Establishing the degree of conservatism associated with the establishment of operating parameters within a binary plant. Help persuade potential users and financial institutions of the viability of a plant designed to incorporate one or more of these concepts.


The technology investigated by this project is presently ready for commercial application. The potential for the application of the supersaturated turbine expansion concept is presently greater than that for the supercritical cycle concepts.

This is in part due to conservatism of the industry in the operation of the binary turbines. The industry is following the status of these investigations, as they represent a potential performance gain without significant modifications to existing facilities. By quantiQing the degree of conservatism currently practiced in defining the turbine inlet conditions, the ongoing investigations will establish “safe” regimes of operation. It will also demonstrate the potential application of the twodimensional nozzle as a monitoring device to provide the turbine operator with an indication of the onset of condensation, before the turbine can be damaged. It is anticipated that if these investigations can confirm that there is not a measurable degradation in performance during these metastable expansions, they will be utilized by the industry within the next 3 to 5 years.

While the technology base for the supercritical cycle concepts is presently better defined and ready for commercialization, industry’s perceptions of the viability of the technology must be changed. This may require demonstration projects and/or cooperative efforts between industry and the Department of Energy to demonstrate both the superior performance of the cycle, as well as its relatively simple operation.

At the conclusion of the research efforts, a power cycle will be available for the liquiddominated hydrothermal resources that combines both simplicity and a performance level approaching that of an idealized power cycle. Unless practical, or real, equipment constraints are significantly altered (very small heat exchanger pinch points, 100% efficient rotating equipment, etc.), there is little more that can be accomplished in terms of improving the cycle performance.

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FY93 ANNUAL PROGRESS REPORT CONVERsroN TECHNOLOGY

Expected Outcome

= Increased utilization of a g e o t h e d resource by up to 28 %. If the resource is produced at a constant rate, this results in a 28% increase in the amount of power being generated. r f the amount of power generated is maintained at a constant level, the technology would result in a 28% reducrion in the amount of geothedj lu id required for the energy conversion system (this could also be considered a 28% increase in the size of the resource).

RT By incorporating the advanced supercritical cycle technologies and achieving the 20% increase in the geothermal fluid utilization, the cost of power generated from a moderate temperature resource weber-type), would decrease by 8% to 13%. Utilization of the supersaturated turbine apansions would result in an additional 8% improvement in the geothermal jluid efleectiveness, producing an additional 2% to 5% decrease in the cost of power.


Mines, G., April 1993. Expansions". DOE Geothermal Program Review XI, Berkeley, CA.

"Investigations of the Condensation Behavior of Supersaturated Turbine

Bliem, C.J. and Mines, G.L., "Advanced Binary Geothermal Cycles; The Find Report of the Heat Cycle Research Program of the U.S. Department of Energy".

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ADVANCED HEAT REJECTION

Background

Geothermal power plants typically use evaporative cooling to reject waste heat, using water derived from steam condensate or from nearby clean water sources. However, from many locations, cooling water is not available in sufficient quantity for evaporative cooling, or conservation of the water extracted from the geothermal field has significant longer-term benefits if reinjected. Some siting restrictions also occur because of sensitivity to steam-plume visibility. Therefore, alternative approaches that limit water consumption in a cost-effective manner are required.

All dry cooling options penalize plant performance severely in most climates because the heat rejection occurs against the dry-bulb air temperature instead of the wet-bulb temperature. All dry-heat rejection has been considered cost-effective in binary plants because they already use a working fluid other than water that cannot be exposed to ambient. However, for steam plants, dry cooling has so far been considered too costly.

One option to conserve water, reduce the overall water requirement, or limit the formation of steam- plumes is to operate both wet and dry heat-exchanger loops in series or parallel, because a small amount of evaporative cooling can significantly reduce the cost of the cooling subsystem. However, the proportion of heat to be rejected by the wet and by the dry subsystems has generally been selected based on the total available water, or to minimize plant parasitics, but not to minimize overall water consumption. A second option is to operate closed heat-rejection loops using fluids other than water (e.g. ammonia, hydrocarbons). A third option is to develop control strategies which optimize plant performance and output as a function of total water consumption. Although this does not save the majority of the water or condensate, the capital costs associated with this option are small or insignificant as compared to the other options.

Objectives

b To characterize various advanced hear-rejection options in terms of perfomuznce and cost.

b To develop a methodology to optimize the costeflectiveness .of heat-rejection subsystems on a basis that accounts for water conservation.

b To determine key design criteria, SpeciJications and operational parameters for heat rejection equipment.

Approach

1) Conduct a comprehensive assessment of the performance of various heat-rejection schemes for geothermal power plants. Considerable information has been developed to model the thermal performance of plants using evaporative cooling as well as condensation or sensible heat exchange to an air system. Predictions of performance and cost estimates for some options were conducted mainly in the mid-70s to early 80s.

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2) Update and expand heat-rejection models to incorporate recent developments in technology, including innovative approaches, direct-contact condensers, advanced heat-exchanger materials, and water- conserving operational strategies. Update or determine the costs of these options.

Organizations

Geothermal Community EPRI, PGgLE

Conventional power plants

3) Conduct an economic analysis in light of the current market and environmental conditions, for particular sites and conditions.

Extent of Interest

Indicated significant interest in the current research.

Research results should be of moderate interest to users of conventional power plants.

4) Collaborate with industry to implement the most cost-effective options. An agreement was reached with PG&E to collaborate on this task and initiate the analysis.


Researchers conducted analysis of the heat rejection system using a detailed computer model that simulates the operation of the plant components, from turbine and condenser through the cooling system, including pumps, pipes and fans. The model optimizes the design and operating parameters of these components. The optimization analysis was carried out in 16 time intervals that described the different ambient conditions found at the site during one year. The simulations were conducted for increasing amounts of water available to be evaporated in the wet towers. The model optimized the number and operating conditions of each component, and predicted how to allocate the total amount of water available for the most effective use during the year.

Two sets of runs were carried out to model the performance of Unit 13 at The Geysers, based on detailed data from PG&E on component performance and costs. The model predictions indicated that significant water could be saved by using dry components, with an average power penalty of a few percent.

The model also provided interesting insight on how the cooling tower should be operated over the year to take the greatest advantage of the limited amount of water to be evaporated. For example, it indicated that much lower air flows to the wet towers than current design suggested and would therefore use a fixed quantity of water more effectively.



10 A cost-@ecti'w increase in power output and longevity of the entire Geysers _field by recovering and injecting up to 9y)percent of the steam condensate with a wetldry cooling retrojit of existing plants, and later recovering the injected fluid as steam.

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ELASTOMER BONDING

Background

To reduce the costs for geothermal wells, it is essential that a number of advanced high temperature elastomer-containing tools such as drillpipe protectors, blow-out-preventors, rotating head seals, and downhole drillmotor stators become available. The small size of the potential geothermal market currently precludes the involvement of the private sector R&D necessary to produce these components. Earlier DOE-funded research performed at L'Garde, Inc. and Brookhaven National Laboratory (BNL) developed a Y-267 EPDM elastomer which meets the design criteria for use in static sealing applications in hydrothermal environments at temperatures up to -315°C. This technology was successfully transferred to industry. Modest changes in the formulation yield products meeting the needs for dynamic sealing in the above mentioned tools.

In FY 1989, the Geothermal Drilling Organization (GDO) initiated contracts administered by Sandia National Laboratories (SNL) with industrial firms to fabricate and test drillpipe protectors and rotating head seals. Future work on blow-out-preventors was planned. In the course of the work on the drillpipe protectors it was determined by the contractor, Regal International, that the lack of a hydrolytically stable chemical coupling system needed to bond high temperature elastomers to metal reinforcement prevented fabrication of a tool which would meet GDO specifications. "he development of advanced blow-out preventors and Moineau stators for downhole pumps was expected to be impacted similarly, thereby adversely afFecting DOE'S ability to meet their goals for reducing well drilling costs.

As a result of material limitations, the Geothermal Division initiated a program in mid-FY 1991 to develop high-temperature ( > 200°C) hydrolytically stable bonding systems.

Objectives

b To identiB and characterize one or more bonding systems.

b To establish cost-shared programs with tool manufacturers to fabricate and test prototype components.

Approach

This activity represented a collaborative effort between BNL, SNL, the GDO, and Regal International, a producer of elastomer products for the oil, gas and geothermal industries.

SNL and the GDO identified needed tools and design specifications. BNL performed applied research to develop bonding systems. This included studying the fundamental interactions that take place at adhesive/substrate interfaces under hydrothermal conditions, and how they were afFected by various reactive groups within the polymer structure. Such an understanding is essential for the molecular design and construction of advanced coating systems and adhesives.

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Regal International was to select promising systems produced at BNL and attempt to use them in the fabrication of prototype and full-scale drillpipe protectors which would then have been field tested by GDO participants. A four-phase procedure was then to be repeated with commercial producers of other tools.

Phase I

Phase II

Phase IIX

Phase N

Use a mechanistic approach to obtain the fundamental knowledge needed to meet the project goals. Obtain information elucidating interactions that occurred at polyaryl-type polymer/conversion coating/metal and pol ymedmetal interfaces. Determine decomposition mechanisms occurring upon exposure to severe environments. Use state-of-the-art analytical techniques.

Laboratory characterization of promising bonding systems. This consisted measurement of the mechanical properties of the systems before and after hydrothermal exposure. Test variables included metallic substrate composition, method of surface pretreatment, adhesive composition, and thickness. Mechanical properties such as bond and tensile strengths were then measured in accordance with the appropriate ASTM standards.

Fabrication of prototype, and contingent upon the results, full-scale drillpipe protectors containing the advanced bonding systems was to be performed at Regal International under GDO sponsorship. Current commercial fabrication methods would have had to be applicable.

After successful engineering-scale evaluations, units would have been field tested by GDO participants.

Generic and specific end-use specifications for the needed systems are outlined below:

Generic Goals

Peel strength (180°), 40 psi on mild steel and stainless steel. Hydrothermal Stability, 90 days in 300" brine.

End-Use Reuuirements (GDO Specifications)

Drillpipe Protectors: No loss of bond after 48 hours in brine at 290°C and 500 psi, or in steam at 260°C and 660 psi while rotating at 100 rpm under a radial load of 3500 lbs.

Rotating Head Seals: No loss of bond after 24 hours in brine at 240°C and 425 psi, or in steam at 200°C and 130 psi.

Blowout prevention Seals: No loss of bond after 90 days exposure to brine at 250°C and 450 psi, or in steam at 200°C and 400 psi.

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Organizations

Geothermal Drilling Organization

Regal International

Drilex

ll

Extent of Interest

Funds cost-shared studies, provides test sites and design specifications.

Producer of drillpipe protectors.

Producer of rotating head seals.

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UNOCAL,

Magma Power Company Central California Power Agency Northern California Power Agency

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GDO participant, user of advanced drilling tools.

Users of advanced drilling tools.

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Researchers terminated all work to synthesize advanced hydrothermally stable chemical coupling systems to bond high temperature elastomers to stainless steel and mild steel at the end of the fiscal year, and prepared a final report.

Some of the critical factors affecting the strength of elastomer-to-metal joint systems which are to be used for geothermal applications were determined. Thermoplastic adhesives are thermally stable up to temperatures of =5500"C, but they have high melting temperatures at which the elastomer begins to degrade. Elasticity measurements confirmed that even at temperatures 50-100°C below the melting temperatures of the adhesives, there existed greater physical changes to EPDMs (both L'Garde and Regal) heated in air than in nitrogen atmospheres. However, peel strength data showed that joints cured in nitrogen did not have comparable strengths to those cured in air, especially when subjected to autoclave exposure.

Tremendous improvements over previously investigated adhesive systems were obtained using certain thermoplastic systems that were cured in air. When previous systems showed only spotty bonding at best after exposure to autoclave conditions for a few hours, some of the air-cured joint systems using the L'Garde EPDM were still completely bonded after more than 13 weeks of exposure to autoclave conditions at 200°C and 200 psi. The strongest bond and the one that was also the most stable to hydrothermal exposure resulted from a joint made of L'Garde EPDM, stainless steel, and a 30 w t l pol yetheretherketone-70 w t l polyphenylethersulfone (PE-1) adhesive applied using a slurry method. No other system matched this strength.

Although some of the joints made with solutions of the thermoplastic polyaryls in various organic solvents had substantid strength with both types of EPDM, exposure to autoclave conditions inevitably resulted in failure. Pastes on the other hand fared better, particularly with the Regal EPDM in which it performed better than both the solution and slurry methods. However, it still did not have peel strengths comparable to that achieved with the PE-1-L'Garde system. The synthesis of polymers containing sulfone, ketone and ether linkages should be further investigated as a viable alternative to the polyaryl thermoplastic blends where the individual melting and glass temperatures may be prohibitive to elastomer integrity.


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Advanced hydrothermally stable chemical coupling systems for use in bonding high temperature elastomers to mild steel and stainless steel reinforcing materials will become commercially available. These systems will extend the service temperature and life of drilling tools such as drillpipe protectors, rotating head seals, blow-out-preventors, and downhole drill motors, thereby reducing drilling costs and improving safety.

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Emected Outcome - Reduce drilling costs by up to IO percent.

IP Reduce the life-cycle cost of electricity fiom liquid dominated reservoirs to 3-7 cents per kilowatthour.

Reduce safety and environmental concerns in drilling operations.


Miura, M., Carciello, N., Sugama, T., and Kukacka, L.E., Oct. 1993. Evaluation of polyaryl adhesives in elastomer-stainless steel joints. BNL 48089.

Kukacka, L.E., 1993. Geothermal materials development activities. Proc. Geothermal Program Review XI, Berkeley, Apr 27-28, 1993, DOE CONF/920484, Washington, 133-140.

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THERMALLY CONDUCTIVE POLYMER CONCRETES

Background

A serious problem in the development of geothermal energy is the lack of cost-effective durable construction materials for handling hot brine, steam, cooling water and binary fluids. Scaling and corrosion are encountered in all geothermal plants, and to various degrees, they adversely affect plant availability, lifetime and power output. These problems are becoming more acute as higher temperature and chemically aggressive fluids are encountered, and ultimately the lack of cost-effective construction materials could seriously constrain the development of the nation's geothermal resources.

The economic utilization of binary working fluids in geothermal energy conversion cycles operating in the 150" to 200°C temperature range would dramatically increase the size of the exploitable hydrothermal resource. Therefore, a key objective of the Geothermal Division Conversion Technology Task is to reduce the cost of power from a binary plant by 8 to 20 percent through improvements in efficiency and in O&M cost components. A major item of cost in a binary plant is the shell and tube heat exchangers, primarily due to the necessity of using high alloy steel tubing to prevent corrosion. Even then, excessive fouling prevents the economic use of binary processes with hypersaline brines. Both problems could possibly be solved with the development of a thin scale resistant thermally conductive polymer matrix composite which could be used as a liner on low cost mild steel tubing.

Cost effective utilization of bottoming cycles in flash processes as a means of increasing energy conversion efficiency will also become possible.

The technical feasibility for the use of high temperature composite materials for corrosion protection was demonstrated by BNL in the early 198Os, and since then they have been used successfully by the geothermal industry. It was then shown that significant increases in the thermal conductivity of the polymer-matrix composites could be achieved by the incorporation of high conductivity materials as fillers. Conductivities approaching those of type410 stainless steel were obtained. In addition, it was shown that the addition of high temperature anti-oxidants into the composite significantly reduced the rate of scale deposition and adhesion to the surface. This initiated work to develop a low cost, low fouling replacement material for the high alloy steels used in geothermal heat exchange applications.

Objectives

To develop a polymer cement composite lined heat exchanger tubing meeting the following criteria: 1) Heat tran@er cmflcient and surjace roughness similar to those of AL-29-4C tubing. 2) Fouling factor < 5Opercent of L 2 9 - 4 C when used in brines typical of the Salton Sea KGRQ, and 3) Cosr not more than nvice that of mild steel.

Approach

Brookhaven National Laboratory (BNL), the National Renewable Energy Laboratory (NREL) and private industry (Red Hill Geothermal) are performing thii work as a collaborative effort. BNL performs the fundamental and applied research necessary to define the polymer cement formulations, determines protective coating thickness requirements, develops methods for the placement of thin, uniform coatings on heat exchanger tubes, and performs post-field test analyses on tubing sections.

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NREL

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NREL conducts engineering analyses and heat transfer tests. This work includes measurements of heat transfer coefficients, cost estimates, and the management of field testing.

Red Hill Geothermal provides a field test site and ancillary equipment at a plant operating at the Salton Sea. Tests in an environment typical of that in a bottoming cycle application in a flash process are being performed.

The R&D is being performed in four phases.

Provides engineering and field project management services.

Phase I

Phase II

Phase IIX

Phase IV

Obtain the fundamental knowledge needed to meet the research goals. Obtain information elucidating interactions that occur between organic polymer binders containing anti-oxidants and reactive thermally conductive fillers in composites. Determine decomposition mechanisms occurring upon exposure to the test environments.

Determine the effects of compositional and processing variables on the resultant properties of the composite. Parameters necessary to centrifugally cast smooth thin uniform composite liners onto long lengths (204) of small diameter (0.75 to 1.0-im.) tubing are then defined.

Fabrication of test tubing at BNL.

Perform field evaluations of a bottoming cycle application in a geothermal flash process as a cost-shared activity with industry. Fluid flow, heat exchange and corrosion resistance characteristics will be measured. Design of full-scale heat exchangers, cost analyses, and, Contingent upon results, fabrication and testing of prototype units will follow.


BNL researchers performed work to optimize the various process parameters for applying a composite liner on the inner surface of small diameter tubings and to determine the minimum thickness required to assure corrosion resistance. NREL researchers completed heat transfer calculations and performed cost evaluations which confinned the potential cost effectiveness of the materials system.

Engineering scale flow tests at Red Hill Geothermal commenced. As of the end of the fiscal year, 230 hours of continuous operation under conditions representative of those in a ''bottoming cycle'' were accrued. Results indicate that the performance of thermally conductive liners applied to carbon steel tubing was comparable to that of more expensive L 4 X N tubings. Under similar operating conditions, the overall heat transfer coefficient for the lined tubing was -9% less than that of the AL4XN. Pressure drop measurements indicated that both materials performed similarly, thereby implying that the rate of fouling or scale buildup in both tubes was the same. Operation for 100 days is planned to substantiate these early results. Contingent upon these results, testing of composite liners containing anti- oxidants to reduce scale deposition, will be performed in FY 1994.


OrganiZat iOnS I htent of Interest

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Red Hill Geothermal UNOCAL cycles in flash processes.

Gas Research Institute

Interested & h h t exchangers for bottoming

Interested in condensing heat exchangers for use in high efficiency gas furnaces.

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If high temperature, scale resistant, thermally conductive, and corrosion resistant liner materials were commercially available they could be used in heat exchanger applications or energy conversion processes. Compared to the use of high alloy steels which are often required to provide corrosion protection, the use of composite liners on mild steel could reduce the tubing cost by a factor of 2 or 3. Polymer lined tubes will have wide applications in binary cycles in geothermal electric generating plants, in district heating systems, solar process heat applications, and chemical processing.

Ewected Outcome

10 Improved electric generation capacities, by up to 10 percent, with the availability of cost- efective materials for use in bottoming cycle heat exchangers.

sr Low temperature geothermal resources, that are currently uneconomical, will become more amactive for development, thereby greatly enhancing the exploitable geothermal reserves.

10 Increased plant utiliztrtion factors due to reduced scale deposition, and decreased quantities of waste sludge for disposal would result fiom the use of binary processes with hypersaline brines.

Publications and Presentations a

8

Webster, R.P., Kukacka, L.E., and Reams, W., Sept. 1992. Development of polymer concrete liners and coatings for use in geothermal applications, BNL 48002. American Concrete Institute Special Publication "Recent Innovations in Polymer Concrete Technology", (in press).

Kukacka, L.E., 1993. Geothermal materials development activities. hoc. Geothermal Program Review XI, Berkeley, CA, Apr 27-28, 1993, DOE CONF/920484, Washington, pp. 133-140.

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FIELD TESTING OF THERMALLY CONDUCTIVE POLYMER CONCRETE

To quculrtifl the heat transfer and anti-corrosion properties of thermcrlly conductive polymer concrete linings developed by Brookhaven Natiolurl Laboratory.

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Background

Heat exchangers are one of the expensive components used in binary power cycles, especially when they are used in geothermal power plants. Currently, expensive alloy metals are used in aggressive geothermal environments and a lower cost substitute is desirable. The field testing of new materials or linings for heat exchangers is of interest to the geothermal industry because it assesses its suitability as a low-cost substitute for use with highly corrosive scaling geofluids.

I Objective

Approach

The National Renewable Energy Laboratory (NREL) and Red Hill Geothermal have jointly undertaken a research task to investigate the heat transfer and anti-corrosion performance of thermally conductive polymer concrete linings (PCL) for use in heat exchangers and compare it to the performance of heat exchangers with conventional high alloy steel tubes. Researchers at NREL conducted analytical simulations under both laboratory and field conditions. The PC lining itself is being developed at Brookhaven National Laboratory (BNL). NREL researchers investigated the effect of the thermal conductivity and thickness of the PC material on the overall heat transfer coefficient of a heat exchanger through a parametric study. NREL planned and proceeded with field experiments to characterize the anti- fouling and anticorrosion performance of PC lined tubes. These experiments were conducted under actual working conditions, using actual geothermal brine at working temperatures and pressures. A Cooperative Research and Development Agreement (CRADA) with Red Hill Geothermal for conducting field tests at the Del Ranch power plant was signed.

The test skid at Del Ranch was used for these tests. The tests involved the exposure of PC lined tubes and other materials such as AL-6XN (a high alloy steel tube) to the geothermal brine. The primary method of characteriziig the anti-fouling and anti-corrosion performance will be to post-test, dissect, and examine the PC lining material.

NREL has taken several actions to avoid problems faced in previous field tests. NREL and Red Hill have decided to relocate the test skid to a location where the brine silica contest was around 295,000 ppm and the brine temperature was about 110°C. This action largely eliminated the possibility of silica precipitation. It was also decided to increase the heat exchanger tube diameter from 0.75 inch outer diameter (used in previous tests) to 1.0 inch. To prevent any scaling on the cooling water side, NREL used a closed cooling loop where a mixture of water and glycol was used as a working fluid.

NREL identified a technique for-inspecting the thickness of the PC lining of 10 feet long carbon steel tubes. In this technique, x-rays were used and detailed images of tubes (in 16 feet long sections) were taken. Resolution of the x-rays was quite high, which allowed detailed pre- and post-test examinations. This technique is commonly used for weld testing. Using this technique, NREL was able to detect problems with non-uniform lining encountered in previous field tests.

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Organization

Magma Operating Co. (formerly Red Hill Geothermal Inc.)

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Extent of Interest

Employ the polymer concrete lining in a binary or bottoming cycle.

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Completed parametric study of the effect of thickness and thermal conductivity of the PCL on the overall performance of carbon steel tubes.

Completed reinstrumentation of the test skid, installed a closed cooling loop, and relocated the test skid to a new location.

Identified a nondestructive technique for measuring the thickness and uniformity of the PCL after application to the base tube.

Started a loo-day field testing and gathered field data.

Conclusions from 250 hours of field testing indicated that the overall heat transfer coefficients of the PC lined tubes were within 10 percent of that of AL-6XN tubes. The fouling rate for both tubes was found to be within 20 percent of each other as well.



A new technology related to the heat exchange side of geothermal power plants is being developed. Heat exchangers will be made of low-cost base metal such as carbon steel and will be lined with PC material that is resistant to corrosion and fouling. The thermal and fouling performance of these low-cost heat exchangers will be comparable to (or better) than the more expensive high alloy stainless steel heat exchangers. Discussions are underway with Babcock & Wicox and Dow Chemical to manufacture heat exchangers with PC linings. During FY94, NREL plans to take steps toward commercialization of PC lined tubes and heat exchangers.

Ewected Outcome

sv Polymer concrete linings could reduce the cost of elemkity by as much as ten percent I I depending upon thefbuling rate of the geothennal resource. I


Three letter reports to DOE and the CRADA partner were publications related to this research. Due to the proprietary nature of this work, no journal or conference publication was prepared.

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WELL CEMENTS

Background

The quality of cementing of a geothermal well completion often establishes the life expectancy of the well. Poor cements can result in blow-outs and casing corrosion or collapse. The conventional use of normal weight (- 14 lb/gal) cement slurries can contribute to the formation of lost circulation zones during completion operations. Therefore, lightweight (- 10 lb/gal) slurries that cure to form hydrothermally durable materials are badly needed.

During the period 1978-85, Brookhaven National Laboratory (BNL) organized and conducted an R&D program to develop and test advanced normal weight cement formulations. This international effort, coordinated through the American Petroleum Institute, involved Universities, private industry and government laboratories culminating with the field testing of several cement formulations cured in-situ under downhole flowing brine conditions. During field tests, the CO, content in the well was low, therefore carbonation resistance was not evaluated. Results from this effort currently serve as the basis for selecting cements used in geothermal well completions throughout the world. Cement slurries that had densities less than 13.6 lb/gal failed to meet the test criteria, identifying a research goal that to date has still not been fully attained.

A recently identified problem that severely reduces well life, and increases costs and environmental concerns, is cement deterioration due to alkali metal catalyzed reactions between CO,-containing brines and the calcium silicate hydrate compounds present in conventional well cements. Rapid reductions in strength, increased permeability, and corrosion on the outside surfaces of the well casing occur. Solving this materials problem is the goal of the current cement research activity.

Objectives

To develop andjield test non-portland cement based materials meeting the following criteria: 1) life tqwctancy, 20 years; 2) Carbonarion rate, < 5 percent a#er 1 year in brine at 3Cx)"C containing 5a)ppm COB* 3) Slurry density, 10 Ib/gal; 4) Pwnpability, 4 hours at 15OOC; 5) Compressive strength, > loo0 at 24 hours age; 6) Bond strength to steel, > 10 psi; 7) H,O pemability, < 0.1 m Darcy; 8) Bulk density, < 62.4 lb/@; and 9) Cost, < $10 per ban.

Approach

Since all conventional calcium silicate hydrate-based cements are subject to reactions with C02, other reaction paths leading to superior cements are identified and elucidated. Emphasis is currently placed on the synthesis of calcium and aluminum phosphate cements formed by acid-base reactions. Reactive lightweight fillers are selected and interactions that occur between them and the cementing matrix under hydrothermal conditions studied. Property characterizations of the cement formulations, in a slurry state and upon curing, are then performed. Retarding admixtures needed to insure pumpability are selected and larger-scale mixing, flow tests, and downhole evaluations conducted. The latter phases are conducted as cost-shared cooperative efforts with geothermal well completion iirms and well owners in a Geothermal Drilling Organization (GDO) coordinated program. Participants include Halliburton Services and Unocal.

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Phase I

Phase II

Phase III

Phase IV

Phase V

Phases N

Fundamental cement research. To synthesize calcium and aluminum phosphate cements, and to elucidate interactions that occur between them and a number of aluminosilicate-based microsphere fillers. State-of-the-art surface science analytical techniques are used.

Mix design. To develop cement-filler mixtures and curing conditions to yield the desired properties.

Property characterization. To determine the mechanical, physical and chemical resistance characteristics of promising formulations before and after autoclave exposures to C0,- containing hydrothermal fluids.

Placement technology. To determine technical feasibility of using cement slurries in well completions using conventional placement technology. This includes selection of retarding admixtures to extend pumpability and verification of this by the performance of consistometer testing in accordance with American Petroleum Institute standards. Industrial assistance in the selection of retarders is contributed by a well service company.

Downhole evaluations. The ability to mix and place cements on a large-scale is verified, and the long-term durability of samples cured in and exposed to downhole geothermal environments is determined. A cost-shared activity with a well service company and a well owner.

and V are conducted as cost-shared GDO coordinated efforts with industry to insure the practicability of the materials and technology transfer.


Researchers successfully completed small-scale laboratory studies to detemine the compatibility of several inorganic and organic microsphere-type fillers with phosphate modified calcium aluminate cements. Results were promising and identified a reaction path for producing a lightweight C0,-resistant well cement. Plans to transfer the technology to industry by means of a Geothermal Drilling Organization (GD0)-sponsored program conducted by BNL, Halliburton Services, and Unocal were formulated and approved. This effort will determine the technical and economic practicability of mixing and placement of large-scale quantities of cement into geothermal wells, and characterize cement properties after long- term downhole exposures at four geothermal sites.

In the laboratory studies, Phases 1-3, lightweight slurries were prepared by incorporating microspheres composed of aluminosilicate hollow microspheres into calcium phosphate pastes. The latter were derived from calcium aluminate cement as a base reactant and sodium polyphosphate (NaP) as the acid reactant. The substitution of NaP for the previously used N H d H 8 0 4 eliminates the formation of NH3 gas as a reaction product during mixing and placement, thereby eliminating a potential environmental concern. Compared to the density of a neat calcium phosphate cement s l u e which is 1.98 gkc, the addition of the microspheres reduced the density to the range 1.1 to 1.5 gkc. The density goal of the program is - 1.2 g/cc (10 lb/gal). These lightweight slurries were then cured in a hydrothermal environment at 200°C or 300°C. The following factors were found to govern the strength development and long-term stability of the cements: 1) phase composition and transformation of the matrix and the interfacial reaction products formed by reactions between the microspheres and the cement, 2) changes in the

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Organizations

Geothermal Drilling Organization

microstructure developed within the matrix and at the matrix-microsphere interface, and 3) the susceptibility of the microspheres to thermal and hydrothermal decomposition. Autoclave exposures of the cured materials to 0.05M N4C03 solutions at temperatures up to 300°C were conducted for times up to 120 days. Compared to conventional class G or H geothermal cements which will form - 10% CaCO, within 7 days in this environment, the advanced cements exhibited < 1 % after 120 days. Other API criteria such as pumpability and strength were also met or exceeded. Halliburton commenced work to determine if the BNL data can be reproduced on an engineering scale.

Extent of Interest

Cost-shared studies.

One extremely promising formulation which appears to meet the API design criteria was identified and a second should be established in FY94. Downhole testing of the first cement should commence in late FY94. Testing of the second formulation will start in FY95. The GDO-sponsored technology transfer activities will require 3 years (FY 94-96) to complete, but much of this will consist of the long-term (1- year) downhole exposure testing phase which requires little manpower.

-~ ~~~~ ~~ ~ ~

Red Hill Geothermal UNOCAL

Specifiers of cements for their wells.


Halliburton Services I Schlumberger I Potential suppliers of cement formulations and I placement services.


An advanced high temperature C0,-resistant lightweight cement meeting all of the API criteria for geothermal well completions will become commercially available.

Ewecfed Outcome

Availability of cements to high (> 5oOppm) CO, containing brines at temperatures > 100°C and well lye extensions up to 20 years.


Sugama, T. and Carciello, N. 1993. "Hydrothermally synthesized aluminum phosphate cements." Adv. Cem. Res., 5,31.

Sugama, T. and Carciello, N. 1993. "Carbonation of calcium phosphate cements after long-term exposure to Na.$03-laden water at 250°C." Cem. Concr. Res., 23, 1409.

Kukacka, L. E. 1993. " Materials for geothermal applications." Proc. Geothermal Program Review XI, Berkeley, CA, pp.

Sugama, T. 1993.

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133-140.

"Phosphate-bonded calcium aluminate cements. " U.S. Patent 5,246,496.

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LOST CIRCULATION CONTROL MATERIALS

Background

The cost of correcting lost circulation problems occurring during well drilling and completion operations constitutes 20 to 30% of the cost of a well. Therefore, a key Geothermal Division objective is to reduce the frequency of lost circulation episodes and the cost associated with their repair. It has been estimated that the availability of chemical formulations which, depending upon the size of the fissures encountered, could be used with or without particulate fibers to rapidly plug lost circulation zones, could result in 47 to 78 percent reductions in repair costs when compared to those for conventional two-plug cement treatments. The greatest savings will occur if the repair materials can be injected through the drillpipe without the necessity of removing the drill bit. This will not only greatly reduce down-time, but also aid in the location of the fractured zones. Other advanced placement techniques under development such as the use of drillable straddle packers or downhole mixing and injection, will also result in significant cost savings if suitable cementing materials can be identified.

Objective

b To reduce well drilling and completion costs by the development of advanced chemical I formulations which can be used-to rapidly plug lost circulation zones. 1

Approach

This project is closely coordinated with well drilling and lost circulation control activities underway at Sandia National Laboratories (SNL). Brookhaven National Laboratory (BNL) participates at meetings of the SNL Industrial Review Panel, at which time the BNL program is reviewed to assure relevance. SNL provided essential test equipment such as a consistometer, slot tester, and a downhole test simulator to BNL for use in the effort. FY 1994-planned larger-scale laboratory and field tests are being coordinated by SNL.

The laboratory effort consists of the development of cementitious formulations compatible with bentonite- containing drilling fluids and which will meet the mechanical and physical property criteria. Selection criteria include pumpability at various temperatures, degree of expansion upon curing, permeability, compatibility with fillers, and strength at early ages.

Specific criteria for the formulations include: 1) viscosity of individual reaction streams < 70 Bc for 6 months at temperatures C 50" and for 24 hours at 50" to 300°C; 2) viscosity of mixed reactants < 70 Bc for 4 hours at 300°C; 3) compressive strength > 5OOpsi at 2 hours age; 4) permeability to water < 1U2 Darcy; 5) volume increase upon curing; 6) durability in Brine at 300°C > 30 days; 7) all constituents environmentally benign; 8) compatible with organic and inorganic particulates, and 9) materials cost < $10 per barrel. Identification of the reaction products formed is made using state-of- the-art analytical techniques.

The most promising formulations are optimized for use with one or more of the placement methods identified by SNL. Small-scale flow tests are then performed in the laboratory under simulated downhole hydrothermal conditions. Larger-scale pumpability and mud displacement tests are then performed as cooperative efforts with SNL.

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The project is organized into four phases:

Organizations

Halliburton Services Schlumberger

UNOCAL Magma Power Company Central California Power Agency Northern California Power Agency

Phase I

Phase II

Phase III

Phase IV

Extent of Interest

Potential supplier for chemical systems and field placement services.

Well owners, potential users of technology.

Cementitious formulations potentially compatible with bentonite contaminated rock formations and/or drilling fluids, and which will meet the materials specifications are selected for evaluation in screening tests. Emphasis is placed upon chemical interactions occurring between the cementing matrix and reactive fillers, and identification of the reaction phases formed.

Mechanical, physical and chemical durability characterization. Tests to determine pumpability at various temperatures, degree of expansion upon curing, and strength at early ages are emphasized.

Optimization of the formulations for use with one or more of the six advanced placement techniques identified by SNL.

Contingent upon these results, larger-scale laboratory and field tests are performed in which the cements and fillers are placed under simulated downhole conditions.


Emphasis of the work performed in FY 1993 was directed towards the possible utilization of calcium phosphate cement formulations for lostcirculation control. If successful, these systems, the major constituent of which is calcium aluminate cement, will be easier to place than previously developed MgO- based formulations, and upon curing, yield higher strength and more durable products. Essentially all of the R&D required before these materials can be used in large-scale above-ground tests at SNL and in downhole evaluations was completed. The physical characteristics of slurry formulations and the mechanical and hydrothermal resistance properties of cured materials were determined. Pumpability at temperatures up to 70°C was verified. Based upon these results, formulations suitable for placement using straddle packer and downhole mixing and injection techniques were identified. Verification of the materials properties in larger-scale testing to be performed in conjunction with SNL must be made before transfer of the technology to industry can be accomplished. These tests were originally scheduled for late FY 1993, but were rescheduled by SNL to FY 1994.


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Advanced lost circulation systems for oil, gas and geothermal wells will become commercially available. These systems will be used with or without bridging-type additives depending upon the size of the fissures to be sealed. They will cure rapidly and predictably over a wide range of formation temperatures and be compatible with a variety of placement techniques. Cementitious grouts will also become available for the repair of Civil Engineering structures and the isolation and stabilization of chemical and radioactive waste storage sites.

Ekpected Outcome

sr Clnnmercial availability of low cost chemical systems which can be used alone or in conjunction with particulate bridging materials, and suitable placement methods that reduce the costs associated with lost circulm-on episodes by 30 percent and yield an overall 10 to I3 percent improvement in fluid production costs.


Kukacka, L.E., 1993. Geothermal materials development activities. Roc. Geothermal Program Review XI, Berkeley, CA, Apr 27-28, 1993, DOE CONF/920484, Washington, 1334.

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ADVANCED BIOCHEMICAL PROCESSES FOR GEOTHERMAL BRINES

Background

Disposal of toxic leachable solid waste in an environmentally and economically acceptable way may be a major impediment to large-scale geothermal development. For example, brines from the Salton Sea geothermal area in California may contain total dissolved solids up to 350,000 ppm. These hypersaline brines lead to the generation of geothermal solid wastes in power plants. Currently, the disposal of these wastes can cost over $1 million per year for a 50 M W geothermal power plant. High disposal costs and the long-term liability associated with hazardous waste disposal provide the incentive for this study.

objective

b To dewlop economic and environmentally acceptable methods for disposal of geothennal wastes and conversion of by-products to use@ forms.

b To develop methods for dissolution, separation and immobilization of geothermal wastes suitable for disposal, usable in inert construction materials, suitable for reinjection into the reservoir fonnaton, or used for recovery of valuable metals.

b To integrate the detoxification, metal recovery, recycling, and waste minimization processes.

Approach

The experimental strategy used at Brookhaven National Laboratory (BNL) for the development of detoxification biotechnology for geothermal waste is based on the use of biochemical methods for dissolution of toxic elements found in geothermal residues. Thus, the produced solution containing toxic and valuable metals can be reinjected or used for concentration and recovery of valuable metals. In the recovery mode, both chemical and biochemical methods are being developed.

Technical feasibility of a technology based on biochemical processes for the conversion of geothermal wastes from hazardous to non-hazardous wastes has been demonstrated. Laboratory scale studies have shown that biotechnology for detoxification of geothermal wastes is versatile and is applicable to a variety of geothermal sludges containing few or many metals whose concentrations may exceed limiting threshold concentrations as recommended by regulatory agencies. Metals such as chromium, copper, manganese, arsenic, mercury, and others, can be removed with 80 to 90 percent efficiencies. Continuing studies aimed at optimization and scaling-up of processes used in the emerging biotechnology indicate that there are several essential process variables which have to be considered in the development of field applications of geothermal waste treatment biotechnology.

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The work is organized in three phases:

Phase I Identification of process type, i.e., chemical or biochemical (biochemical identified as best candidate). Determination of system and choice of microorganisms. Development of thermophilic microorganisms which operate at 50" to 60°C and pH 1 to 2. Multi-element kinetic studies. Bench model bioprocesses. Comparison of bioreactors. Choice of bioreactors for scaling-up .

Phase II First generation of scaled-up fluidized bed and agitated tank bioreactors, and first full process design. Economic and technical feasibility studies based on expertise gained in phase I. Indicate cost-efficient, environmentally acceptable process in hand. Identification and optimization of process variables including automation. Parallel studies for metal recovery technology and production of clean water. Completed construction of 3-bioreactor 50-gallon system pilot-plant. Removal of radionuclides. Secondary Biochemical process defined and tested. Process optimization studies.

Phase III Bacterial culture recycling. Optimization of radionuclide removal. PG&E Waste Stream bioprocess defined, field application under discussion. Comparison of (chemical vs. biochemical) MAGMA samples initiated. Analysis and Bioprocessing of hot dry rock fluids initiated. Integrated processing for metal and salt recovery potential.


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Completed an economic evaluation of two different bioreactor designs using several different loadings (10, 20,30, and 40 percent) and several hours of residence times. The results were used to develop a computer program for the Advanced Biochemical Processing.

Although state+f-the-art design and/or best materials have not been taken into consideration, differences in the cost of various processes stress further the importance of loading, residence time, and the type of bioreactor. This study has also indicated the importance of process quality control and appropriate monitoring needs.

A first generation pilot-plant was constructed and is being tested.

A second bioprocess for the removal of radionuclides has been identified and tested.

Under the experimental condition used, sludge loadings of up to 40 percent are practical and at temperatures of > 50°C fast rates of 10 hours or less are achievable at the pilot-scale level.

Studies at elevated temperatures have also indicated that particular attention has to be paid to construction materials, compressors, pumps, and other equipment needed for an efficient detoxification process.

Initiated study of metal recovery processes due to environmental consideration. Current results indicate that an 80 to 90 percent metals recovery is possible in the form of small concentrate. The final aqueous phase meets drinking water standards.

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Pacific Gas & Electric

Magma Operating Co.

Currently negotiating a CRADA andlor joint venture R&D effort.

Joint venture in process. r

Educational programs have proved to be successful and are continuing as part of the on-going R&D under the auspices of BNL and DOE Geothermal Division educational programs.


In addition to the geothermal interest, there is considerable spin-off interest in the oil and gas, food, and other environmental cleanup areas.


Availability of a new environmentally acceptable technology, based on biochemical processes, for the cleanup of geothermal wastes which is economically and technically feasible. Application of this technology can achieve further process cost savings by (a) reactants recycling, (b) metal and salt recovery, (c) adjusting to specific needs as demanded by different chemistries of geothermal sludges and brines.

The benefits that will result from this technology will be both environmental and economical. Not only will the detoxification be less expensive, but the end products will be useful. Recovered metals will have market value. The detoxified sludges can have such uses as landfills. The emerging biotechnology could find applications in other industries, for detoxifying wastes or recovering metals.

The economic and regulatory significance of the new biotechnology can be described by the following examples.

In 1985, the graded cost for type II-I disposal was $200 per ton and $75 per ton for non-hazardous waste. The non-hazardous waste was defined as that not exceeding the total threshold limit concentration (TI'LC) and soluble threshold limit concentration (STLC). Examples in the table below show the regulatory concentrations and those after the biotreatment (BIOT) of Chromium VI.

Thus, an 80 percent removal of the metals represents a 60 percent saving. It is to be understood, however, that the cost of disposal and long term liabilities are continuously increasing, while the available space for disposal is diminishing. For example, at BNL, disposal of a similar sludge cost $500 per ton in 1991. The corresponding non-regulated waste disposal cost was $100 per ton. If the sludge contains

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in addition to chromium and lead, say radium, then it has to be shipped at a cost of $400 per cubic foot. On the other hand, removal of the metals leaving radium alone produces waste costing $76 per cubic foot to dispose of or $10,800 and $2052 per ton respectively. This represents a five-fold saving already achievable on a laboratory scale.

Ekpected Outcome

LP An expanded resource base that will accelerate development of geothennul energy in areas of the country where it is currently considered commercially marginal.

Reduced reliance on importedfuers through the use of an indigenous resource.

Lower cost of power derived through advances in energy conversion eflciency, advanced materials, and techniques.


Premuzic, E.T., M.S. Lin, and J.Z. Jin, 1993. Geothermal Waste Treatment Biotechnology. Proceedings Geothermal Program Review XI, "Geothermal Energy - The Environmentally Responsible Energy Technology for the Nineties," Berkeley, CA/

Premuzic, E.T., M.S. Lin, and J.Z. Jin, 1993. Recent Developments in Geothermal Waste Treatment Biotechnology. Proceedings "Heavy Metals in the Environment," Toronto.

Premuzic, E.T., M.S. Lin, and J.Z. Jin, 1992. Biotechnology. Geothermics, v01.21, No. 516, pp. 891-899.

Developments in Geothermal Waste Treatment

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FY93 ANNUAL PROGRESS REPORT DIRECT HEAT APPLICATIONS

BOISE CITY

Background

Development of the Boise geothermal system has been slowed due to insufficient funds for optimal operation of the geothermal system. To partially correct this situation, Congress appropriated funds for drilling of an injection well or other system enhancements for the Boise City system.

Objective I w To accomplish system enhancements by siting and drilling an injection well, and increase the

capacity of the Boise City geothennal system.

Approach

Boise City will locate and drill an injection well if feasibility studies indicate that such a well would improve the long term operation of the reservoir. If funding permits, other enhancements to the City's system will be pursued.

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The cooperative agreement was not in place until the beginning of FY 1993, so the only work on the project was that done by Boise City utilizing their own funds. Boise City is nearing completion of studies of the reservoir which will be used in the decision to site and drill an injection well.


NIA


This project will enable Boise City enhance operation of the City's geothermal system and will demonstrate injection into low-temperature geothermal systems.

E-ected Outcome

IQ More encietu use of the geothermal resource, reservoirfluid conservm'on by use of injection, and expansion of the system without untoward e#ects on neighboring users of the resource.


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LOW-TEMPERATURE RESOURCE ASSESSMENT

Background

Low- and moderate-temperature resources are widely distributed through the 15 western states, and the enormous potential of these resources is greatly underutilized. Conversion from fossil-fuel energy to geothermal for collocated users will reduce hydrocarbon energy consumption and associated user environmental degradation. Potential industrial and community users require an inventory of known resources. The last national resource inventory concluded in the early 1980's is outdated.

Objective

b To achieve greater utilization of the notion 3 widely dism-buted low- to moderate-temperature geothermal energy resources.

Approach

For low- and nwdemte-tempemtu~ hydrothermal resources, the Idaho Water Resources Research Institute (IDWRRI), the Geo-Heat Center (GHC), and the University of Utah Research Institute (UURI), through subcontracts with the Idaho National Engineering Laboratory, are: 1) updating existing inventories of resources, 2) prioritizing resource sites for possible development based on proximity to users, resource quality and economics, 3) developing better techniques to explore for, delineate, test and evaluate these resources, and 4) providing outreach to potential developers and users.

For g e o t h e d heatpumps, the aforementioned groups are: 1) evaluating the cost-effectiveness of using GHPs over other equipment and energy sources, 2) determining the potential for penetration of the heating and cooling mark&, and how it can be accelerated, 3) compiling and disseminating information on soil types, subsurface temperatures, drilling conditions, and availability, regulation and temperature of ground water to assist in the design of ground loops for GHP systems, and 4) assessing the R&D needs of the GHP industry.

Educational activities involve: 1) the design and publication of 3 brochures on geothermal energy specifically targeted at potential user groups, 2) filming of a broadcastquality video, in cooperation with geothermal companies, that can be shown by network, cable and public television stations, 3) liaison with the public on geothermal topics in general and on the results of this project in particular, and 4) outreach to geothermal developers, utilities, and regulators to promote the benefits of hydrothermal and GHP use.

IDWRRI, GHC, and UURI are working closely with scientists and engineers from the State Coupled Resource Assessment and State Energy Office teams and state water-resource organizations.

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c Geothermal Resource Areas

-Temperature Program

}Temperatures above 100°C (212O

Temperature below 100°C (212°F) Arc8 Suitable for Geothermal Heat Pumps (Entire US.)

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ETgure 20. Low temperature resource map of the United States


State resource teams for Utah, Idaho, Oregon, Nevada, and Californi were identified, statements of work developed, and subcontracts negotiated with state teams from August 1992 to February 1993. State resource teams completed reviewing a preliminary GHC collocation study and are reviewing and updating resource inventories for their respective states (see Figure 20). Data from GEOTHERM, WATSTORE, and other sources are examined, compared, evaluated and merged into comprehensive geothermal resource databases for each of the ten states. UURI and GHC coordinate state team efforts. UURI and the Utah Geological Survey (UGS) hosted a meeting of program participants to discuss data formats and project problems. UURI completed much of the 10 fluid chemistry analyses allocated to each state team, results are being incorporated to the fluid chemistry databases.

Funding to the state teams was available over a nine-month interval. Six teams have nearly completed the database and resource maps. The Utah and Idaho teams presented results at the 1993 Annual Geothermal Resources Council meeting in October (Blackett, 1993, Dansart and Mink, 1993). All state team subcontracts will be extended to June 30, 1994. Preliminary results from several state teams show a substantial increase in the number of low- to moderatetemperature wells, or thermal wells and springs

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Collocated City Governments Greenhouse and Aquaculture Developers

I]

Interested in resource database and potential applications.

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in the 1993 database compared to the 1980-82 database: California, 979 in 1993 vs 635 in 1980-82; Colorado 170 vs 120; Utah 713 vs 315; and Washington 971 vs 368. An indirect but very significant result is the renewed interest in geothermal resources by several state agencies, including possible internal funding for geothermal investigations.

UURI completed and distributed fact sheets describing residential and commercial GHP case histories. In addition, UURI hosted downsites for two heating and cooling teleconferences promoting GHP information and development. IWRRI presented preliminary results of a nationwide study of geothermal heat pump viability. Further, IDWRRI completed a mapping project that delineates geological and hydrological conditions suitable for geothermal heat pumps.

GHC collected and interpreted engineering data on 217 case studies across the U.S. on the performance of residential and commercial geothermal heat pumps (GHP). Results drawn from the comparative energy survey indicate that GHP technology is effective in saving energy over all other electrical heating systems. Energy savings on the order of 15 to 35 percent over air-source (ASHP) systems, and 25 to 60 percent over electric resistance systems can be achieved. The savings for a residential system in $/year over an ASHP system was typically found to be in the range of $200 to $350/year (cost calculated @ $0.075/kWh). Compared to non-electric heating systems the GHP was found to save significant energy costs (35 to 58 percent) over liquefied petroleum gas (LPG) systems but with little to no savings over natural gas systems.

Results of the peak power reduction survey indicate that significant peak power (kW) reductions can be achieved for winter peaking utilities, on the order of 2-7 kW per home. Summer peaking reduction is slight and in some cases insignificant, typically on the order of 0-1 kW. Based on contacts with 57 utilities, GHPs are seen as peak reducing DSM tools. Many utilities offer incentives of some kind including: average rebates of $382/unit to residential and $133/ton to commercial customers, low cost loans, discounted electric rates (about $0.01 kwh), and add-on rebates for desuperheaters. Barriers to market entry are higher initial costs ($2,000 to $3,000 for a 3-ton unit) than other HVAC systems. This is due to incremental costs of ground loops and lack of an infrastructure of ground loop contractors and dealers. More than 18,OOO GHP systems (3-ton equivalent) have resulted from 34 programs. The main benefits to utilities are load leveling, conservation and customer satisfaction.


I Organizations I Extent of Interest I California Division of Mines and Geology Colorado Geological Survey Montana Bureau of Mines and Geology Southwest Technology Development Institute Oregon Department of Geology and Mineral

Utah Geological Survey Nevada Bureau of Mines and Geology Washington Division of Mineral Resources

Resources

Participants in updating the resource inventory. I

128



Research results will be widely distributed increasing geothermal heating up to possibly 100 mW, for greenhouses, district heating systems, and agricultural/industrial processes. Such an increase in geothermal heat will benefit the ongoing greenhouse expansions in New Mexico and Utah, and the aquaculture expansions in Arizona and Idaho.

Achieving the objectives of the project throughout the 10 western states could result in conversion of an estimated 64 trillion Btu/yr (15 X lob BOE) from fossil fuel to geothermal energy utilization for district heating in 254 cities; in addition, greenhouses and industrial processes could also add to the total by the year 2000. Further, rapid growth of geothermal heat pump technology throughout the United States, at a rate of 200,000 to 400,OOO units per year, could amount to approximately 1 .O Quad by the year 2010.

~~

Ekpected Outcome

mr Identification of resources suitable for near-tern utilization.

Preliminary reservoir information (temperature, depth, jlow rate) for selected resources.

.D Updated state resource inventories Jbr ten states.

mr Contacts between potential resource users, state resource teams, GHC, UURI and I?XURI. - Assistance to Dotential resource users.


Blackett, R.E., 1993. "A new geothermal database for Utah." GRC Transactions, v. 17, pp. 91-96.

Dansart, W.J., and Mink, L.L., 1993. "Overview of geothermal investigations in Idaho, 1980 to 1992." GRC Transactions, v. 17, pp. 409-415.

Freeman, K.M., and Mink, L.L., 1993. "Geographical viability of ground water geothermal heat pumps in the United States." GRC Transactions, v. 17, pp. 297-301.

Balckett, R., 1993. "A new Geothermal Database for Utah." GHC Bulletin, v.15, n.2, pp. 11-16.

Culver, G., 1993. "Well Costs." OIT Geo-Heat Center, p. 3.

Lineau, P. and Ross, H., 1993. "Low-Temperature Resource Assessment Program." Proceedings Geothermal Program Review XI, pp. 169-172.

Rafferty, K., 1993. "Transmission Line Economics Spreadsheet." GHC Bulletin, p. 10.

Lineau, P.J., and Ross, H.P., 1993. "Low-temperature resource assessment program. " Proceedings Geothermal Program Review XI, pp. 169-172.

Wright, P.M., and Colvin, S.L., 1993. "Geothermal heat pump systems: the ABC's of GHPs." GRC Transactions, v. 17, pp. 303-314.

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LOW-TEMPERATURE APPLICATIONS

Background

The Geo-Heat Center (GHC) located at the Oregon Institute of Technology conducts research and provides assistance to stimulate utilization of the large direct-heat resource base in the United States. The GHC’s activities include: 1) technical and development assistance, 2) research to aid in devising solutions to resource and technical development problems of direct-heat projects, and 3) distribution of information and educational materials to stimulate development.

Objectives

b To provide technical assistance to developers of direct use projects for space heating, geothennal heat pumps, greenhouses, aquaculture and industrial applications.

b To pefonn appropriate RdiD to reduce the cost of installing and operating direct use projects.

b To publish informational and educationul materials and maintain a library to aid researchers and developers of geothennal direct use projects.

Approach

The GHC’s approach is to provide technical assistance (TA) to prospective geothermal users on resource data, preliminary engineering design, analysis of operational problems and technical information. The program is designed to introduce the potential user and engineering consultant to geothermal direct-heat applications. The presence of a proven and reliable source of technical advice to the consultant is critical in promoting their initial involvement with an unfamiliar resource. The GHC also performs selective R&D to address direct use technology problems and needs. Further, the GHC publishes educational materials to aid engineers in the design of direct use projects.


GHC’s technical assistance program handled 345 requests for technical and development assistance on geothermal direct use projects. These requests for assistance included: space and district heating (59, geothermal heat pumps (79, greenhouses (19), aquaculture (14), industrial (15), electric power (ll), resource/well (65), equipment (27), and other (64). Additionally, the design for a pilot fruit dehydrator (to dry pears) at Los Azufies, Mexico, was completed.

R&D activities included evaluation of lineshaft vertical turbine pump problems, geothermal district heating marketing strategy, and greenhouse peaking analysis. Specific pump failures were evaluated in terms of pump description, symptoms, inspection results, and conclusions for: 1) Susanville district heating system well, 2) Modoc High School well, 3) College of Southern Idaho well, and 4) a well at Paisley, Oregon.

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FY93 ANNUAL PROGRESS REPORT DIREn HEAT APPLICATIONS

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Local Governments Technical assistance for district heating projects and marketing.

Technical assistance for direct-heat projects. Geothermal Developers

Pump Manufacturers Improved pump design.

The GHC is assisting the city of Klamath Falls in marketing the city’s geothermal district heating system to commercial building owners in the downtown core area. The marketing approach eliminates heat exchangers and energy meters and offers heat on a flat rate basis.

In response to a request from Colorado, an addition has been made to the previously developed GHS (Greenhouse Heating Systems) spreadsheet. The addition allows calculation of fuel use by a non- geothermal (propane, electric, fuel oil, etc.) peak heating system.

Publication of the GHC Quarterly Bulletin (v.14, n.34, and v.15, n.1-2) was continued, a Geothermal Library of 4,572 volumes was maintained, 7 technical papers were prepared, 14 presentations were given, 8 tours were conducted, and 26 progress monitor reports were prepared.



The success of this project will mean more rapid penetration of geothermal direct use into the energy sector. This will translate into more energy savings and reduced greenhouse gases due to more geothermal direct-heat projects being on-line. Improvements in design of downhole pumps and marketing strategies will be provided. Further, stimulation of geothermal direct-heat use by publication of Bulletins on the progress and development of geothermal projects, technical papers, and software tours, and other educational materials will be provided to interested parties.


Culver, G., 1992. Low-Temperature Direct Use Wells: GRC Drilling Well Control and Regulatory School, p.3.

Lienau, P. and Lund, J., 1992. Significant Events in the Development of Geothermal Direct Use in the U.S. GRC Bulletin, v.14, no.3, pp. 1-8.

Lund, J. 1992. Geothermal Spas in Czechoslovakia. GRC Transactions v.16, pp. 3-7.

Rafferty, K. 1993. Klamath Falls Geothermal District Heating System. Oregon Business Magazine

Raf€erty, K. 1993. Geothermal Direct Uses. Eastern Hot Dry Rock Report, p. 3.

Rafferty, K., 1993. Direct Use Geothermal Applications for Brazed Plate Heat Exchangers. GHC Bulletin, v.15, no.1, pp. 7-12.

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Organizations

State of New Mexico

Potential Users of geothermal resources for direct use

Q Extent of Interest

Cost-shared the project.

Interested in the economics of cascaded direct- use applications. u

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Rafferty, K., 1993. Marketing the Klamath Falls Geothermal District Heating System. GHC Bulletin, v.15, no.1, pp. 4-6.

Cascaded Direct-Use Application


The Southwestern Technology and Development Institute in New Mexico has partially completed construction of an aquaculture facility that will be using the spent geothermal fluid from a nearby greenhouse. This project will demonstrate the economics of direct-use cascaded applications.



The Southwestern Technology and Development Institute will test the prototype cascaded facility and provide operating and economic data to the geothermal direct-use community. Cascaded geothermal applications utilize a higher percentage of the available heat thereby decreasing the load on the resource and decreasing the use of other energy resources. Availability of data will enhance the use of cascaded geothermal applications.

I Ewected Outcome

lhm.$er of technology, related to direa use of geothennal resources, to the developers of geothermal projects.

1 e Heightened awareness of geothermal energy 's benefls in the private and utility sectors. I

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FY93 A.NNUfi PROGRESS REPORT DIRECT HEAT APPLICATIONS

GEOTHERMAL HEAT PUMPS

Background

Geothermal Heat Pumps (GHP) have gained international attention as a proven means of energy conservation and demand reduction (see Figure 21). However, the high first cost for residential and commercial heating and cooling applications is a major obstacle to market penetration of this technology. A research program is needed to find ways to reduce installation costs and increase performance and, therefore, increase the marketability and effectiveness of the GHP technology. There is also a general lack of awareness about this technology in the HVAC community.

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Objectives

b To obtain a higher level of understanding of existing GHP technology, performance, and costs.

b To apply geothermal or the other appropriate R&D technologies to understand and improve GHP systems. Reduce the installed costs of GHP system by 25percent or more.

b To increase GHP market penetration and effectiveness as a commercial and residential heating and cooling source.

Approach

The program consists of four basic elements: 1) Monitoring and documenting the performance of existing GHP hardware to confirm the savings expected from this technique and to identify areas for improvement. 2) Development of advanced concepts for constructing improved geothermal heat exchangers and confirming their performance. 3) Reviewing and summarizing existing techniques for vertical (drilled) loop installations and suggesting research to be made and implemented. 4) Finally, providing technical support for the DOE efforts to market and increase awareness of the GHP concept.


Conducted literature reviews on R&D progress, toured GHP installations, and attended IGSHPA conferences. Found that R&D is lacking and the industry relies on conservative design criteria that have worked in the past.

Issued GHP related contracts to Stockton State College and Ft. Polk to expand the GHP performance database.

Designed and installed an instrumented vertical ground loop at SNL to measure heat transfer coefficients and compare the relative performance of various heat exchanger designs. Testing will be conducted in this year (1994).

Began an assessment of the effect of higher thermal conductivity backfill materials on the ground heat exchanger performance. Preliminary results indicate a promising improvement and opportunity for decreasing the heat exchanger loop lengths.

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Oklahoma State University

U.S. Army

Atlantic Electric

IGSHPA

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Compared current industry ground loop design software with other analytical techniques. Comparisons were good. More experimental data comparisons are needed to verify findings.

Extent of Interest

Tech Transfer Partner

Contractor

Utility Partner

GHP Trade Association

Utility Trade Association

GROUND-COUPLZD HEAT PUMP ,REFRIGERANT

Agure 21. Schematic diagram of a geothermal heat pump installation.

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NRECA Rural Electric Coop Ass’n I Loop Tech International Vertical Loop Installer I

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FY93 ANNUAL PROGRESS REPORT DIRECT HEAT APPLEATIONS


The efforts realized in this project will yield an expanded database on the performance of GHPs. This database will include parameters measured on the heat pump and ground loop equipment that should be useful to identify areas of improvement needed in this technology. More efficient heat exchanger designs that are less costly to install and installation methods which are more reliable and cost-effective will become available. Further, GHP technology awareness within the HVAC industry will increase leading to an increased market penetration of GHPs.

The near-term applicability of the research probably deals with the vertical installation survey being conducted. The use of vertical installation methods is limited in this field, and the survey may allow local drillers, without the experience of installing GHP loops, to benefit from the experience of others - thereby reducing vertical installation costs.

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Ekpected Outcome - Installation of 400,000 GHP units annually by the year 2000 thereby reducing peak demand by as much as 5000 Mwe and energy consumption for space heating by 0.1 quad.


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