Chapter 1_Formation Evaluation_Dr. Adel Salem

Formation Evaluation [PEP 437]

Dr. Adel Salem Asst. Prof. of Petroleum Engineering Faculty of Petroleum and Min. Eng. Suez Canal University Spring Semester 2010-2011

Course Outlines

Chapter one: Methods of Gathering Formation Evaluation Data Chapter Two: Mud Logging Chapter Three: Measurements While Drilling Chapter Four: Coring Chapter Five: Wireline Logging Operations Chapter six: Open-Hole Logging Measurements Chapter Seven: Analysis of Logs and Cores Chapter Eight: Formation Testing (DST) Chapter Nine: Integrated Formation Evaluation

Formation Evaluation-PEP437_Dr. Adel Salem March 27, 2011 Chapter 1: 2

Chapter Outlines Introduction FE Definition The Scope of Formation Evaluation Formation Evaluation Formation Evaluation Methods 1. MUD LOGGING

Mud Logging Two Events

2. CORING Coring Conventional Cores Information from Cores Sidewall Sampling Sidewall Coring Tool Coring Sidewall

Formation Evaluation-PEP437_Dr. Adel Salem March 27, 2011

3. MEASUREMENTS WHILE DRILLING 4. TESTING 5. OPEN-HOLE LOGGING

Basic Well Logging Tools Introduction - What Is Logging?

6. MODERN LOGGING TOOLS Open Hole logging Tools Well Log Interpretation Properties Logs Actually Measure

Chapter 1: 3

Introduction In petroleum exploration and development, formation evaluation is used to determine the ability of a borehole to produce petroleum. Essentially, it is the process of "recognizing a commercial well when you drill one". formation evaluation The detailed analysis and interpretation of borehole data, drilling results, geophysical downhole logs, etc., to determine the physical characteristics of the rock formation through which the drill has penetrated. This is done mainly to ascertain whether or not economic reserves of hydrocarbons are present and, if they are, to determine the most economical and efficient way to extract them. Formation evaluation is an important component of reservoir engineering design.

March 27, 2011 Formation Evaluation-PEP437_Dr. Adel Salem Chapter 1: 4

FE Definition: Schlumberger Dict. The measurement and analysis of formation and fluid properties through examination of formation cuttings or through the use of tools integrated into the bottomhole assembly while drilling, or conveyed on wireline or drillpipe after a borehole has been drilled. Formation evaluation is performed to assess the quantity and producibility of fluids from a reservoir. Formation evaluation guides wellsite decisions, such as placement of perforations and hydraulic fracture stages, and reservoir development and production planning.


The Scope Of Formation Evaluation Formation evaluation covers a very large range of measurement and analytic techniques. Although the emphasis will be on well logging techniques and log analysis methods, these are not the only tools available to the formation evaluator. Well logs are central only in the sense that they are universally recorded in practically all well bores and are directly relatable to all the other parameters available from the associated sciences.


Formation Evaluation The initial discovery of a reservoir lies squarely in the hands of the explorationist using seismic records, gravity, and magnetics. Formation evaluation presupposes that a reservoir has been located and is to be defined by drilling as few wells as possible. In those wells, enough data should be gathered to extrapolate reservoir parameters fieldwide to arrive at realistic figures for both the economic evaluation of the reservoir and the planning of the optimum recovery method. Formation evaluation offers a way of gathering the data needed for both economic analysis and production planning.


Formation Evaluation What then are the parameters the manager, the geologist, the geophysicist, and the reservoir and production engineers need? \ Which of them can be provided by seismic records, by coring, by mud logging, by testing, or by conventional logging?



Formation Evaluation, The geophysicist needs to know the time-depth relationship

in order to calibrate conventional seismic and vertical seismic profile (VSP) surveys.

The geologist needs to know the stratigraphy of the

formations, the structural and sedimentary features, and the mineralogy of the formations through which the well was drilled.

The reservoir engineer needs to know the vertical and lateral

extent of the reservoir and its porosity (type of porosity) and permeability, fluid content, and recoverability.


Formation Evaluation, The production engineer needs to know the rock properties; be

aware of overpressure if it exists; and be able to assess sanding and associated problems and the need for secondary recovery efforts or pressure maintenance.

Once the well is on production, the production engineer will also need to know the dynamic behavior of the well under production conditions and need to diagnose problems as the well ages. The engineer may also need to know formation injectivity and residual water saturations to plan water flooding and be able to monitor the progress of the waterflood when it is operational.


Formation Evaluation, The manager needs to know the vital inputs to an economic study, namely,

the original hydrocarbon in place; recoverability; cost of development; and, based on those factors, the profitability of producing the reservoir.

Log measurements, when properly calibrated, can give the majority of the parameters required. Specifically, logs can provide either a direct measurement or a good indication of: Porosity, both primary and secondary (fractures and vugs) Permeability Water saturation and hydrocarbon movability Hydrocarbon type (oil, gas, or condensate) Lithology Formation dip and structure Sedimentary environment Travel times of elastic waves in a formation

From these data, good estimates may be made of the reservoir size and the hydrocarbons in place.


Formation Evaluation, Logging techniques in cased holes can provide much of the data needed to monitor primary production and also to gauge the applicability of water flooding and monitor its progress when installed. In producing wells, logging can provide measurements of: Flow rates Fluid type Pressure Residual oil saturations From these measurements, dynamic well behavior can be understood better, remedial work planned, and secondary or tertiary recovery proposals evaluated and monitored.


Formation Evaluation Methods In practice the order in which formation evaluation methods are used tends to follow the orders-of-magnitude table, that is, from the macroscopic to the microscopic. Thus, a prospective structure will first be defined by seismic records, gravity, and/or magnetics. A wellbore drilled through such a structure may employ mud logging and/or measurements while drilling (MWD); and, in that wellbore, cores may be cut or sidewall samples taken. Once the well has reached some prescribed depth, logs will be run. An initial analysis of mud log shows, together with initial log analysis, may indicate zones that merit testing either by wire line formation testing or by drillstem testing. Should such tests prove the formation to be productive, more exhaustive analysis is made of all available data including core analysis. The whole process can be summarized by table .3.



1. MUD LOGGING Mud logging, more elegantly referred to as hydrocarbon mud logging, is a process whereby the circulating mud and cuttings in a well being drilled are continuously monitored by a variety of sensors. The combined analysis of all the measurements provides indications of the rock type and its fluid content. The sundry measurements are displayed on a log as curves or notations as a function of depth. Not all wells are logged in this manner. Development wells, for example, are usually drilled and logged by wireline logging tools only. Wildcat wells, however, are nearly always monitored by the mud-logging process. The great merits of mud logging include the availability on a semicontinuous basis of actual formation cuttings analysis and the ability to predict drilling problems (such as overpressure) before they become unmanageable.


Mud Logging

First information during drilling Mud weight Rotary speed Weight on bit Cuttings analysis Gas content pH Mud salinity


Two Events

Real-time events Fluid volumes, ROP, WOB, RPM, SPM, FFR

Time-lapsed events: Rock chips, gas/oil shows, fluids & chemical,

temperature


2. CORING A number of methods are in use to cut cores in a well bore. Conventional cores are cut using a special core bit whereby a long core barrel is retrieved and brought back to surface. The sample of the formation so recovered may undergo physical changes on its journey from the bottom of the well, where it is cut, to the surface, where it can be analyzed. More sophisticated coring mechanisms are now in use that conserve either the orientation, the pressure, or the original fluid saturations of the rock sample gathered. An awareness of these methods is essential to an understanding of core analysis results. Other coring methods are available for cases where additional rock samples are required after the well has been drilled and before it has been cased. These methods require wire line tools that cut core plugs from the side of the well. Many of the parameters needed to interpret open-hole wireline logs correctly can only be determined from accurate core analysis. This presupposes that cores have been cut. Thus, in the initial stages of a field development, coring plays an essential part.


Coring - Conventional

Taking a core requires that the regular drill bit be removed from the hole. It is replaced with a "core bit", which is capable of grinding out and retrieving the heavy cylinder of rock. The core bit is usually coated with small, sharp diamonds that can grind through the hardest rock. A core bit cuts very slowly. A core is a solid cylinder of rock about 4-5 inches in diameter, and a single core will usually be about 30 feet long.


Cores

Allow direct measurement of reservoir properties Used to correlate indirect measurements, such as wireline/LWD logs Used to test compatibility of injection fluids Used to predict borehole stability Used to estimate probability of formation failure and sand production


Information from Cores

Porosity Horizontal permeability to air Grain density

Vertical permeability to air Relative permeability Capillary pressure Cementation exponent (m) and saturation exponent (n)

Standard Analysis Special Core Analysis

March 27, 2011 Formation Evaluation-PEP437 Dr. Adel Salem

24

PDC Cutters

Fluid vent

Drill collar connection

Inner barrel

Outer barrel

Thrust bearing

Core retaining ring

Core bit

Coring Assembly and Core Bit


Coring - Conventional

Whole Core Slab Core March 27, 2011 Formation Evaluation-PEP437_Dr. Adel Salem Chapter 1: 26

(Whole Core Photograph, Misoa Sandstone, Venezuela)

Whole Core


Sidewall Sampling Gun

Core bullets

Core sample

Formation rock


Sidewall Coring Tool

Coring bit

Samples


Coring - Sidewall

This method is cheaper than the conventional coring. Cores can be taken in hours, instead of days. In sidewall coring, a slim wireline coring tool is run into the hole. The tool may be of two general types; either "rotary sidewall" or "percussion". Typically, cores about 1" in diameter and 1" to 2" long can be retrieved with this method.


Coring - Sidewall


Coring - Sidewall


3. MEASUREMENTS WHILE DRILLING

Increasingly today, formation properties are being measured at the time the formation is drilled by use of special drill collars that house measuring devices. These measurement-while-drilling (MWD) tools are particularly valuable in deviated offshore wells where well bore path control is critical and where an immediate knowledge of the formation properties is vital for decision making on such matters as the choice of logging and casing points. Although not as complete as open-hole logs, the measurements obtained by MWD are rapidly becoming just as accurate and usable in log analysis procedures.


Motor Surface-adjustable

bent housing

Inclination RPM gravity toolface

Stabilizer and bearings

Measurement antenna

Azimuthal resistivity (depth of investigation

12 in. or less) Gamma ray

detector

3/4 fixed bent housing

Transmitter for wireless telemetry and measurement

of current

Logging While Drilling


Logging While Drilling (LWD)

Provides: Real time correlation for picking coring and

casing points Real time overpressure detection in exploration

wells Real time logging to minimize out of target

sections (geosteering) Real time formation evaluation to facilitate stop

drilling decisions


4. TESTING Formation testing is the proof of the pudding. If the well flows hydrocarbons on a drill stem test, no amount of logging data or core analysis can deny that a productive zone has been found. However, a drillstem test (DST) not only provides proof that hydrocarbons exist in the formation and will flow but also supplies vital data regarding both the capacity of the reservoir and its ability to produce in the long term. Correct interpretation of pressure records from drillstem tests adds immensely to the overall formation evaluation task. Wireline formation testers complement drillstem tests by their ability to sample many different horizons in the well and produce not only fluid samples but also detailed formation pressure data that are almost impossible to obtain from a DST alone.


5. OPEN-HOLE LOGGING Open-hole logging provides the great meeting place of all of the other formation evaluation methods. Only through open-hole logging can a continuous record of measurement versus depth be made of so many formation properties. In particular, wireline logs can record formation electrical resistivity, bulk density, natural and induced radioactivity, hydrogen content, and elastic modulae. These raw measurements can then be interpreted to give a continuous measurement-versus-depth record of formation properties such as porosity, water saturation, and rock type. Almost without exception, every well drilled for hydrocarbons is logged with wireline instruments. Unfortunately, the logs so acquired are not always analyzed in detail or are incorrectly analyzed because of a lack of training on the part of the analyst or a lack of understanding of where wireline logs fit with relation to the other methods of formation evaluation.


Basic Well Logging Tools Lithology Tools

Spontaneous Potential Gamma Ray

Fluids Identification Tools Resistivity

Petrophysical Tools Porosity

Neutron Density Sonic

Auxiliary Tools Caliper


Introduction - What Is Logging?

In situ meas. (vs. depth) of Rock properties Fluid properties

When Openhole (before casing)

While drilling (LWD / MWD) After drilling (wireline)

Cased hole Interpretation for

Geological properties Petrophysical properties Production properties

Casing

Open hole


Formation Evaluation Methods


6. MODERN LOGGING TOOLS The actual running of a log involves as much the tool on the end of the logging cable as the cable itself and the surface controlling and recording apparatus. The component of logging tool is illustrated.


WIRELINE LOGGING EQUIPMENT


Open Hole logging Tools The open-hole logging tools in use today are: 1. Formation Fluid Content Indicators

Induction Laterolog Micro focused (microresistivity) Dielectric Pulsed neutron Inelastic gamma

2. Porosity-Lithology Indicators Sonic (acoustic) Density and lithologic density Neutron Natural gamma ray Spectral gamma ray NMR (CMR and MRIL)


3. Reservoir Geometry Indicators Dipmeter Borehole gravimeter Ultra long spacing electric

4. Formation Productivity Indicators Formation tester

These basic devices will answer 90% of the questions about the formation. Omitted from the list are various types of old logs (such as electric logs) and some standard auxiliary devices which, while important, do not rate as separate tools since they always piggy back along with one or another of the basic tools. Among those auxiliary tools are:

Spontaneous potential (SP) log Caliper log


Openhole Well Logs

Formation Evaluation-PEP437_Dr. Adel Salem March 27, 2011

Passive measurements Gamma ray: Indicates lithology Spontaneous potential: Indicates

lithology Caliper: Hole condition

Active measurements

Resistivity: Fluid saturation, fluid type

Porosity: Rock properties, quantity of hydrocarbon

Density: Rock properties, seismic response

Sonic log: Rock properties, seismic response

Cap rock

Reservoir rock Source rock

Oil

Chapter 1: 45

Well Log Interpretation Logs provide detailed essential information on wells and reservoirs

Well

Depth

Rock type Porosity Fluid type Fluid volume Height Fissures Permeability

Granite

Sandstone

Limestone

Shale

Claystone


Natural radioactivity: Gamma

Electrical potential: SP

Electron density: Density

Acoustic travel time: Sonic

Hydrocarbon index: Neutron

Photoelectric absorption: Density

Properties Logs Actually Measure


Your Curriculum



References 1. Richard M. Bateman : Open-hole Log Analysis and Formation

Evaluation, International Human Resources Development Corporation, Boston, ISBN 0-88746-060-7 (U.S.), 1985.

2. Halliburton : Formation Evaluation Manual, HLS 3. D. G. Bowen : Formation Evaluation and Petrophysics, Core

Laboratories, Jakarta, Indonesia, March 2003. 4. Heriot-Watt University Formation Evaluation, Institute of

Petroleum Engineering, 5. Toby Darling : Well Logging and Formation Evaluation, Gulf

Professional Publishing is an imprint of Elsevier Science, Elsevier, 2005.


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