The Three “Fives”

Five Key Findings

1. If reservoir pressure is not reliably considered and if formation face pressure is not reliably represented, any sort of diagnostic or predictive methods are potentially in significant error. Trivial - but essential concept. Tools are available for representing these features in fundamental, continuous injection monitoring evaluations.

2. Consequences include inability to plan when treatments are carried out and to recognize fundamental degradation in injectivity, misinterpretation of pressure transient data, inadequate/inappropriate support, incorrect decisions on the type of intervention that is required, if any. Many reservoirs are being fractured and it has not been appreciated except by specialists - sweep considerations, etc.

Five Key Findings

The PEA-23 concepts can be extended/modified to quantify discrete events representing extension/growth of fractures/discontinuities even in unconsolidated formations. More quantification is required in the next three months using available data. Data are available for calibrated available models.

Consequences: Design tools and “vision,” stimulation planning and optimization investment for maintaining injectivity

Five Key Findings

There can be a point of diminishing or no return in stimulation beyond which further “conventional” stimulation will provide progressively less effective results.

Consequences: Methods are being developed to represent this during the current phase of the project using back-analysis of available injection history. Stimulation types can be refined – using this and the concepts in Key Finding 2.

Five Key Findings

Near-wellbore skin, particularly completion skin is an under-appreciated feature in comprehending injection programs.

Consequences: It can be huge in soft formations and misrepresent required stimulation/intervention, it can possibly be manipulated to achieve improved conformance, it may entail significant perforation fillup in soft formations and its magnitude and impact can vary depending on whether injection is above or below fracture opening/reopening pressure.

Five Key Findings The complexity of fracture growth in consolidated and in soft

formations is such that planar, single fracture, constant height or ellipsoidal fracture models may be inadequate in many cases. Consider cases where they will be inadequate – in layered reservoirs with significant stress or permeability contrast where fracture or matrix fingering dominates, in weakly consolidated reservoirs?, in reservoirs where there are multiple fractures that are created by pressure cycling (does not even need to be batch injection), in untuned reservoirs with injection just below fracture extension pressures, in naturally fractured reservoirs treated at low (or possibly cycled) injection rates.

Consequences: Cautious or selective use of LEFM, wellbore and completion must be reliably represented, disposal domain concepts may be a pre-requisite. Vertical fracture growth must be represented.

Five Key Achievements(not prioritized)

1. Availability of Data Acquisition of data! Archiving of data! Using data! Although it has been slow, the development of the

database and the interpretation of the data are approaching the point where information is being more effectively archived and processed.

Before the end of this phase, more needs to be completed. Much of the intellectual maturation in this project has come about from looking at trends in and features of available data by a diverse group.

Five Key Achievements(not prioritized)

2. Development/Organization and Ultimate Deployment of Analytical Tools

Completions Worksheet PWRAD Multilateral/Multifracture Models Stimulation Selection Tool Thermal and Poroelastic Stress Tool Data Management Capabilities (BHP, plotting …) Others

Five Key Achievements(not prioritized)

3. Knowledge Management/Best Practices/Assurance

Consolidation of available findings Prioritization of key issues as “Best Practices” Supplementary information for design and

procedural limitations Methodology for logically archiving and providing

accessibility. Surface facilities component

Five Key Achievements(not prioritized)

4. Workshops, Exposure and Interaction

Presentation of case studies Shared experience and platform for communication Constructive criticism by a diverse audience Exposure to experience from other disciplines Enforced “motivation”

Five Key Achievements(not prioritized)

5. Recognition of Concepts, Methods, Limitations and Future Requirements

Definition of inadequacies in current testing methodologies (e.g. SRT, falloff in layered formations)

Definition of limitations in modelling methodologies Consolidation and outlining of various options for

completions and stimulation (e.g., conformance methods, procedures for bringing horizontals on-line, the future role of intelligent completions, ESSs, fiber optics, indirect appreciation of the economics of surface treatment versus stimulation, possible occurrence of a compacted zone …)

Five Main RecommendationsTasks 1 and 2: Maintenance and Updating of Tools,

Best Practices, Database

Would seem desirable as data has driven much of project (database)

Even through the duration of the project, opinions and conceptual appreciation has evolved

Additional high quality data is anticipated from upcoming or ongoing pilots and field programs.

Maintaining communication amongst diverse group Tools developed not necessarily envisioned at start

 

Monthly Web HostingTask 1: Maintenance (one year period of performance)Continue with the web site. Revamp/improve as necessary.Brian Odette to coordinate web site.John McLennan to coordinate content.Estimated budget is $18,800 (includes $650 per month for hosting)

Five Main RecommendationsTask 2: Continued Evaluation of Incoming Data

and Upgrading, Conceiving and Implementing New Tools and Best Practices

Improvements and consolidation to the database and Toolbox systems that have been developed.

Maintenance, additions to and further development of Toolbox and Best Practices.

All contractors would participate. Estimated budget $40,000.

Five Main RecommendationsTask 3: Case Studies

Each Sponsor will be requested to continue to provide field data. This data may in fact be superior to some of the historical data that have been provided because of improvements in instrumentation, acquisition, and experience/knowledge. Information will be incorporated into the database system and evaluated with specific intent of testing/improving tools that have been developed, conceiving/recommending/developing of

new tools, concepts, learnings and identifying physical behavior. Estimated Budget of $75,000.

Five Main RecommendationsTask 4: Workshops Two workshops are planned – one after six months and one after nine months Each of these will be designed to look at new technologies and at new and recent developments or events. Recommended that the first Workshop cover horizontal injectors and that the second Workshop would incorporate important aspects from all of the Tasks in the first phase of the JIP. Will be quarterly meetings, two of which will coincide with the Workshops. Estimate budget for organization/coordination is $5,000.

Five Main RecommendationsTask 5: Miscellaneous Accounting /Contractual: It is desirable to keep the level of charging to the minimum. It is perceived that this effort should not exceed two days per month at a non-senior

personnel level. Potentially, a quantity of money could be allocated to GTI to help in any transition period ($5,000?). Over a one-year period of performance it is anticipated that normal accounting/contractual functions could be performed for ~$16,800.

Management: Recording and posting of minutes, coordination, interaction with Sponsors on performance issues and interaction with Contractors to improve delivery, etc. ($24,000). Travel: Will need to be preauthorized for four travel sessions (quarterly). Estimated at $60,000.

Five Six Main Recommendations

Task 6: New Tool Developments

Diagnostic Methods (e.g. PTA methods) Predictive Model (PWSIM) Completions Skin Tool Economics Module

Diagnostic Methods?

In many cases, pressure transient techniques are the only methods that are readily available for interpreting behavior of PWRI wells.

The complexity of the processes can render pressure signatures very difficult to reliably and/or uniquely interpret.

What is a work program for developing techniques to infer fracture characteristics?

Optimize the cost of the testing and maximize the amount of information that can be extracted

External plugging on fracture face

Lf

Internal cake (k damage)

Dilation zoneCompaction zone

Fracture tip plugging

Questions Can a PTA test (or sequence of tests) be designed to identify the

postulated features of the process? What type of test and what test parameters are necessary to

“catch” the data signatures? Is it necessary to shut in the injector prior to the test or can the test

be a continuous part of a normal injection schedule? Is it possible to design tests to separate the fracture effects from

reservoir geomechanics effects (i.e., obtain information about fracture dimensions/plugging as well as about altered reservoir permeability changes)?

Can the data be analyzed by analytical PTA techniques (at least partially)?

What other tools exist or need to be developed to analyze the data and identify the PWRI mechanisms controlling injectivity?

Development of Monitoring Techniques

Generate signatures for a range of parameters describing the damage zones at different stages of injection Investigate the issue of fracture closure and whether it can be determined from falloff data only.

Investigate differences in response between a test that includes a shut-in prior to the test itself with one without a shut-in and make recommendations.

Develop guidelines for the types of tests and testing parameters (rates, stage sizes, length of falloff…).

Incorporation in the Best Practices section.

Completions Skin Tool

To develop a component of the Toolbox To identify if completion skin can be

significant part of the problem To predict how the skin varies for a

given range of design parameters. This will allow decisions as to whether

the optimization of completion skin is necessary and/or possible.

Completions Skin Tool Focus on cased and perforated completions,

screens and slotted liners. For cased and perforated completions,

modeling methodology has already been presented to account for geometry, plugging and collapse and turbulence effects.

Based on detailed modeling of the perforating pattern geometry and permeability damage in laminar as well as turbulent flow, using the DE&S’ PERF3D software.

Lp

Spacing (spf)

Phasing

re

rw

altered zones

dp

Completions Skin Tool

The approach will be to develop general correlations with sufficient number of parameters to characterize the completion skin as a function of perforation design parameters, damage and/or collapse parameters and turbulence.

For screens and liners, the literature review will be extended and complemented by data from JIP members.

General correlations will be then derived from the data.

Completions Skin Tool1) Carry out literature survey and solicit additional

data from JIP participants2) Evaluate all data and develop correlations for skin3) Determine the parameters and their range of

interest4) Generate pressure drop and skin results for all

configurations by varying systematically the parameters

5) Establish correlations from the generated database

6) Package correlations into a spreadsheet-based tool to evaluate completion skin.

Ideal/Necessary? Requirements of a Predictive Model (PWSIM)

Three-Dimensional Fracture Using best available technology and

algorithms.This is a major consideration.

Injection into layered formations is poorly understood and cannot readily be represented without some sort of model.

Interact with available data.

Ideal Requirements of a Predictive Model

Disposal Domain:Evidence from drill cuttings injectionEvidence of shearing behavior for low

rate hydraulic fracturing Batch operations, rate reductionsHow are all of the volumes stored?

Ideal RequirementsDisposal Domain:

The model will need to have the ability to represent multiple planar fractures of different extents.

This characteristic of the disposal domain concept is a potential real advance over existing fracture models.

Some hydraulic fracturing models now take only approximate measures for representing multiple fractures - account for it arbitrarily by imposing arbitrary near-wellbore pressure drops to artificially account for near-wellbore tortuosity and rate partitioning.

How are Naturally Fractured Reservoirs Accommodated?

Ideal Requirements

Layered Formations:Essential that the potential for growth into

different zones with different stresses and plugging characteristics are incorporated.

Becomes essential that a fundamental three-dimensional model is used for the fracture rather than a pseudo-three-dimensional model.

Ideal RequirementsLayered Formations:

The potential irregularity of the geometry with fingering, recession, differential plugging etc. cannot be readily modeled with a fracture code that is based on a modified elliptical geometry.

This is a critical component and can allow extension of pressure transient theory to allow more adequate determination of behavior in layered media.

Necessary RequirementsInitiation:Key feature! It is required to represent radial injection stages

that may precede fracture initiation and propagation.

It will need to adequately represent near-wellbore plugging and thermal effects (as in an Elf model and the BP multilateral model, have a criterion for establishing when radial injection ends and when fracture injection (either hydraulic or thermal) starts to dominate).

Ideal/Necessary? RequirementsInitiation:

Use near-wellbore stress calculations to allow for the generation and propagation of multiple, discrete fractures.

The initiation module will desirably need to be developed to represent stress conditions and single/multiple fracturing associated with inclined wellbores?

Explicit incorporation of “radial” and “linear” flow mechanisms accounting for matrix and fracture injection further demands ability to represent closure, recession and partially opened, finite conductivity fractures.

There is a natural evolution from radial to fractured injection and vice versa or a combination.

Ideal Requirements

Wellbore:There is more to the wellbore than the initiation. Drawing from wok on pressure drops through

completions, the actual completion will be physically coupled to the model to represent associated completion pressure drops.

It is reasonable that the wellbore is included as something other than a line source simplification!

 

Ideal Requirements Wellbore Friction and Temperature:

Relying on analytical techniques developed in the first phase of the Project, can rudimentary wellbore friction and temperature routines will be incorporated.

The importance of these concepts has been clearly demonstrated in Stevens et al., 2000. “The work has shown that fractures tend to initiate in the most permeable regions [this was in the context of seawater injection] as cooling is greater and are typically of smaller vertical extent than the reservoir.”

Can the injection initiation zone be implicitly determined by the model?

Can multiple fractures in different zones be represented?

Ideal/Necessary Requirements How are Soft Formations Represented?

It is desirable to have a model that can represent general constitutive properties for the fracture’s compliant behavior and in the reservoir itself.

This is not a significant issue in classical hydraulic fracturing models which assume homogeneous and elastic behavior.

It becomes more complicated in the so-called soft formations.

The problem with soft formations during isothermal injection may be more elastic than during production - at least remote from the fracture.

Ideal Requirements

 How are Soft Formations Represented?Actually, the problem with soft formations during

isothermal injection may be more elastic than during production at least remote from the fracture.

This is well demonstrated in work by Smit and de Waals and from standard soil mechanics consolidation theory.

It does become more complicated when thermo- and poroelastic stress modifications are incorporated.

Necessary? Requirements

 How are Soft Formations Represented?Around the fracture, even for isoporo-isothermal

simplifications, the deformation characteristics are more difficult to represent.

It is hypothesized that there is the potential for dilatant behavior immediately around the fracture, although changes in stresses tangential to the fracture plane may ameliorate this effect.

Further, it is speculated, with some evidence that beyond this dilatant zone, conservation of mass will dictate a local regime of compactive behavior.

Necessary RequirementsPluggingSaturation Changes, Relative Permeability

Effects and Sweep:Poroelastic and Thermal Effects:

This requires incorporation of PVT effects and stress changes due to thermal effects.

Flexibility for Inputting Multiple Injection Rates and Fluids:This is merely consistent with the capabilities of currently

existing hydraulic fracturing models and operational reality. It is not necessarily trivial because of the required

representations in the reservoir away from the fracture.

Practical Issues:Methodology: Finely gridded modular solution? Will it be a pop-in module and what are the consequences of meshing with a commercial

simulator? Standalone package by adjusting the boundary conditions? Functionelles? The premise is that the fracture simulation is carried out and the block

containing the fracture is modified, as is the injection so that the equivalent behavior can be generated strictly by matrix injection through a centrally located well alone. Presumably this would need to require modifications of q, p, kx, ky, kz and saturations.

Disadvantages of simplified reservoir solution?How does it interact with the available reservoir simulators – GEOSIM is private

– VIPS does not have an open architecture, ECLIPSE’s open architecture does not apply immediate access to flow. How can it be done.

Talk about gridding.Give a step by step procedure.

Practical Issues:What is the the development language?Any artificial intelligence or explicit coupling to

the database?What platform will the code run on?How does it interact with the available

reservoir simulators – GEOSIM is private – VIP does not have an open architecture, ECLIPSE’s open architecture does not apply immediate access to flow. How will it be done?

Conclusion

There is demonstrated need for a more sophisticated tool.

What are the specs and what can realistically done with the available time and budget?

Conclusions

Precaution for any of these Sub-Tasks

No White Elephants