Carbonate Petrophysics

Transcription

1 Carbonate Petrophysics 30 pu Limestone Jerry Lucia Rudist: Middle East Well Evaluation Review# 15, 1994 Schlumberger High Permeability Grainstone: Pt Petrophysical and dgeomechanical Issues in Carbonate Oilfields. Austin Boyd R. E. (Gene) Ballay, PhD

2 Carbonate Petrophysics Course philosophy Draw material from a variety of sources SPWLA, SPE, AAPG, Leading Edge, etc Service Companies Carefully reference every source to allow Client follow-up Illustrate issues with actual data to every degree possible Include parameters and equations Facilitate seamless Client application of course material Distribute spreadsheets to allow Client What If calculations Do Not Champion any particular Tool / Technique Discuss strengths and weaknesses

3 Course objective Carbonate Petrophysics Integrate across discipline and scale and timeframes Wireline (and LWD) measurements are typically the basis for field development and depletion Ultimate objective is an integrated / calibrated interpretation of that data Produced fluid properties and rates: both oil and water Wellbore trajectory and reservoir boundaries Reservoir Depositional Environment and subsequent diagenesis Time-lapse reservoir monitoring with wireline tools Basic Wireline Data Visual Core Descriptions Special Core Data Routine Core Data Wellbore Images: Rock character and reservoir geometry

4 Course deliverables Carbonate Petrophysics Digital, Key Word Searchable PDFs Presentation Exercises Can be worked during class or used as Question / Answer review Manual Related Rltdto the Presentation tti (above) (b as a Text tbook kis related ltd to a Classroom Presentation Spreadsheets used to construct supporting graphics Illustrates exactly how exhibits were developed Allow Client What If variations as need arises

5 Course time-line Three day Carbonate Petrophysics Suitable for abbreviated Time Frames Five day Includes additional Tool / Technique Theory & Illustrations Both options assume a basic comfort level with Wireline / LWD measurements and discipline integrated petrophysical analyses

6 Five Day Carbonate Petrophysics Gus Archie introduced the world to the term petrophysics in This fundamental vision was followed by a carbonate classification system in 1952 in which he commented in discussing the petrophysics of limestones, it is necessary to first classify them, the field application of petrophysical relationships in limestone can be much more difficult than in sandstone, because of variations in pore size distribution. This course begins with a contrast of sandstone and carbonate depositional environments, diagenesis and routine log signatures. Basic capillary pressure techniques are then introduced, thereby setting the stage for the Lucia Petrophysical Classification Robert E Ballay, LLC

7 Five Day Carbonate Petrophysics The Lucia System recognizes that if one is to characterize the relationship between rock fabric and petrophysical parameters, then the pore space must be classified as it exists today, in terms of petrophysical properties. The focus is then on petrophysical properties and not genesis. Key issues are interparticle vs vuggy porosity separate vs touching vugs In addition to basic porosity (magnitude) determination, one should thus also consider pore size and pore type. Common porosity tools (density, neutron and sonic) ) are introduced, and then contrasted as a means of achieving this objective. Image logs and nuclear magnetic resonance are investigated as modern alternative, vuggy porosity identification options. Vuggy porosity affects not only rock quality (porosity vs permeability), but also the Archie m exponent, as is illustrated with laboratory measurements and thin sections. Cementation exponent models, for estimating m as a function of vuggy porosity content, are developed and evaluated Robert E Ballay, LLC

8 Five Day Carbonate Petrophysics In the years since Archie s ground-breaking work, a number of so-called non-archie (ie non-resistivity-based) formation evaluation approaches have become possible Each methodology is developed and then evaluated, with actual carbonate data Pulsed neutron Dielectric Borehole gravity meter Nuclear magnetic resonance Since NMR is the most commonly used alternative, it receives the most attention Basic NMR is followed by Carbonate NMR Carbonate NMR addresses two key carbonate limitations pore size coupling vuggy porosity of sufficient size that surface relaxation no longer dominates the tool response In addition to non-archie formation evaluation, the Specialty Sonic offers Shear Wave identification / orientation of fractures and Stoneley Wave permeability estimates 2008 Robert E Ballay, LLC

9 Five Day Carbonate Petrophysics Additional, supplemental tools / techniques that are investigated in the Course include Visualization by CT Scan Laboratory determination of mineralogy (XRD/XRF/etc) Laboratory measurement of porosity Pressure profiles Quick Look formation evaluation (Sw from resistivity ratio, etc) Double D Dt Duty PikttPlt Pickett Plots Bulk volume water and / or Permeability grids, superimposed on routine PP Grids of constant BVW values can be displayed on the Pickett Plot BVW=Constant, for a specific Rock Type, will generally identify water-free production Sw BVW = Constant BVW=0.015 BVW=0.03 BVW=0.10 Increasing Grain Size Porosity Porosity Sw=1.00 Sw=0.5 Sw=0.3 Sw=0.10 BVW=0.015 BVW=0.03 BVW=0.10 Pickett Plot (m=2.0/n=2.0) Resistivity Grids below the Sw = 100 % line are for visual reference only Locally appropriate permeability relations can be super-imposed on the Pickett Plot At a specific porosity, increases in Pickett Plot (m=2.0/n=2.0) resistivity infer increased permeability 1.00 (lower Swi => better rock quality) At a specific resistivity, lower Sw=1.00 porosities infer lower perms, and Sw=0.5 higher h Swi Sw=0.3 Perm estimate is only valid far above the transition zone Linear extrapolation to left of Sw=100 % line (graphic at right) is for visual reference only Porosity 0.10 Sw=0.15 Perm=0.1 Perm=1.0 Perm=10 Perm= Resistivity

10 Day 1 Start Stop Duration Topic Course Introduction Carbonate vs Sandstone Break Thin Sections Lucia Petrophysical Classification Break Lucia Classification (+ Exercise) Lunch Capillary Pressure (+ Exercise) Break Rock Quality and Cutoffs Break CT Scan with Carb Examples GR in Carbonate (+ Exercise) Review and Feedback In the clastic world, GR activity is often (but not always) a result of clay, and therefore indicative of a decrease in rock quality In carbonates it s not uncommon to find the GR being driven by uranium, in a fashion that is not necessarily indicative of rock quality The presence of uranium, and the associated higher h GR, can signal stylolites, fractures, super-perm and / or general increases or decreases in quality and / or mineralogy One key distinction between sand and carbonate is then the utility and meaning (or lack thereof) of SP / GR response Five Day Carbonate Petrophysics Day 2 Start Stop Duration Topic Sonic in Carbonate (+ Exercise) Break Carb Rhob / Pef (+ Exercise) Break Carb LWD Rhob / Pef Carbonate Neutron Lunch Carb Neutron (+ Exercise) Break Identification of Vuggy Porosity Break Specialty Sonic in Carb (+ Exercise) Review and Feedback Carbonate versus Sandstone Trend parallel to LS line, but offset Pef is qualitative, not quantitative Higher GR corresponds to better quality limestone and increase in dolomitization Black points are invalid data (ie ignore) Limestone generally clean, throughout LS GR activity was essentially all uranium Dolomite is higher non-uranium GR activity Did dolomitization occur in rock which was depositionally different? Uranium has been removed!

11 Five Day Carbonate Petrophysics Day 3 Day 4 Start Stop Duration Topic Start Stop Duration Topic Phi / Mineralogy from Core Quick klook ktechniques XRD/XRF/etc Mineralogy Pickett Plot Break Break Resistivity Tools & Constraints Pickett Plot (+ Exercise) Archie's 'm' Exponent Pulsed Neutron Log Break Break Archie's 'm' Exp (+ Exercise) PNL (+ Exercise) Lunch Lunch Cmnt Exp Variations & Pore Geometry PNL Log-inject-log "m" Estimates From Vuggy Porosity Ratio Break Break BH Gravity Meter "m" Estimates From Vuggy Porosity Ratio Archie s n Exponent (+ Exercise) Pressure Profiles (+ Exercise) Break Break Low Resistivity Pay in Carbonates Correlation Techniques Review and Feedback Review and Feedback Carbonate - Diagenesis includes...dissolution Surface example of how carbonate reservoir rock can be modified. One key distinction between sand and carbonate is that of clay effects versus pore size distribution Eureka Springs, Arkansas Environmental scanning electron microscope images, scale bar is 100 mm at left and 200 mm at right. On the left, a crystalline dolomite with φ= 47% and m = On the right, a moldic bioclastic packstone with φ = 36% and m = This large variation in m illustrates the importance of rock texture on petrophysical evaluation. Electrical Properties of Porous Rocks by Carlos Torres-Verdín, University of Texas In many regards, a key distinction between sand and carbonate, is also one of accounting for clay conductivity short circuits versus variations in pore system tortuosity associated with changes from intercrystalline / interparticle to vuggy porosity.

12 Five Day Carbonate Petrophysics Day 5 Start Stop Duration Topic Image Log (+ Exercise) Break Dielectric Log Wireline "m" Estimates Compared to Core Break Basic NMR (+ Exercise) Lunch Basic NMR (Hydrocarbon Effects) Carbonate NMR Break Carbonate NMR (+ Exercise) Core Calibrated Wireline "m" Estimates Break Daily Review and Feedback Jerry Lucia: Here is how it works Course Summary Carbonate Bluffs along Steel Creek, NW Arkansas Ozark Mtns Road Cut, SW Missouri 2008 Robert E Ballay, LLC

13 Uncertainty in Archie s Equation Where to spend time, and money, in search of an improved Sw estimate Identifying the Biggest Bang for the Buck Identifying the Biggest Bang for the Buck Chen & Fang s results have been coded to an Excel spreadsheet, to facilitate locale specific, digital evaluation Identifying the Biggest Bang for the Buck Chen & Fang performed a differential analysis of Archie s equation to allow an In Depth look at uncertainty in Sw, as a function of input attribute values and respective uncertainties They yproduced generic charts to facilitate locale specific evaluation Their results have been coded to an Excel spreadsheet, to facilitate locale specific, digital evaluation Supplemental Discussions Attribute Sensitivity Analysis, continued In general each attribute may have an individual uncertainty As a second illustration, consider a = 1.0, y a = 0% Rw = 0.02, y Rw = 4.4% R t = 40, y Rt = 1% Phi = 0.20, y Phi = 15% m = 2.0, 20 y m = 10% n = 2.0, y n = 5% Chen & Fang s generalized chart at right reveals C m > C Phi > C n Exhibit following At Φ ~ 20 pu, for stated conditions, i the saturation exponent is a relatively minor issue H. C. Chen and J. H. Fang. Sensitivity Analysis of the Parameters in Archie s Water Saturation Equation. The Log Analyst. Sept Oct 1986 Identifying the Biggest Bang for the Buck Chen & Fang s results have been coded to an Excel spreadsheet, to facilitate locale l specific, digital i evaluation These same relations may be coded into nearly any petrophysical s/w package, to facilitate foot-by-foot evaluation Attribute Sensitivity Analysis, continued The relative uncertainties are a function of the magnitude of the porosity Dropping porosity to 10 % also alters the order of the uncertainties and requires a complete refocus on where Biggest Bang For The Buck is to be found a = 1.0, y a = 0% Rw = 0.02, y Rw = 4.4% R t = 40, y Rt = 1% Phi = 0.10, y Phi = 15% m = 2.0, y m = 10% n = 2.0, y n = 5% At Φ ~ 10 pu, tortuosity in the pore system is far more important than n variations Attribute Uncertainties Specified Individually Light Green Cells require User Specification Light Blue Cells are calculated results The generalized chart and spreadsheet, both Individual Best Relative Un indicate Attribute Uncertainty Estimate On Sw(Arch a 0.0% % Rw 4.4% % C m >> C Phi >> C n Phi 15.0% % m 10.0% % Exhibit following n 5.0% % Rt 1.0% % Sw 22% H. C. Chen and J. H. Fang. Sw^n 5% Sensitivity Analysis of the Parameters in Archie s Water Saturation Equation. The Sw^n=0.367 Log Analyst. is an Sept inflection Oct point 1986

14 Monte Carlo Modeling with Excel One issue of interest is the dependence of Sw upon individual attribute values / uncertainties With the values specified at right Sw(mean) = σ (Sw) = Monte Carlo Simulation of Sw(Archie) 350 Sw Distribution With illustrative applications to Reserve Volumes and Sw(Archie) There is a 95% likelihood that Sw is contained within + / - 2 σ Monte Carlo simulation allows one to determine σ for any possible input distribution, and to therefore identify where the biggest bang for the buck in reducing Sw uncertainty is at Exhibit following Supplemental Discussions Monte Carlo with Excel Monte Carlo with Excel Histogram with 100 samples Excel s RAND() will provide the random numbers required for the multiple, Monte Carlo passes. Multiple passes are required and one must ensure that sufficient passes have been done to result in a representative simulation Exhibit following 14 Multiple passes are required and one must 12 ensure that sufficient passes have been 10 done to result in a representative simulation 8 6 In general, one expects a uniform 4 distribution of random numbers, between 0 2 &1 0 The population distribution associated with 100 samples cast into ten bins has discrepancies ranging from 6 => 14, about an expected mean value of 10, or about 40% The population distribution associated with 500 samples, cast into ten bins ranges from 40 => 65, about an expected mean value of 50, or about 25% This indicates that at least 500 samples,and ideally more, are required for the Excel Random Number generator simulation Frequency Bin Histogram with 500 samples

15 Precision, Accuracy and Uncertainty What Are The Differences And What Can We Do About It? Modeling and Forecasting An Alternative (or supplement) To Experience Statistical Definitions and Illustrations Statistical Definitions and Illustrations Accuracy vs Precision Examples from Every Day Petrophysics Data Normalization Simple linear models x on y, RMA and x on y Pitfalls associated with routine displays Depth oriented and logarithmic Stochastic systems and Monte Carlo modeling Normal, Log Normal and Triangular Distributions Monte Carlo with Excel GeoStatistics and the Variogram Illustrative Applications Supplemental Discussions Statistical Definitions and Illustrations Accuracy is the degree of correctness while precision is the degree of reproducibility. Precision is sometimes thought of as two components: Repeatability: the variation arising when all efforts are made to keep conditions constant by using the same instrument and operator, and repeating during a short time period. Reproducibility: the variation arising using the same measurement process among different instruments and operators, and over longer time periods. Accurate,, but with Low Precision Precision is usually characterized in terms of the standard deviation of the measurements. One standard deviation encompasses 68.3% of the measurements, two sigma 95% and three sigma 99.7%. Accurate,, but with Low Precision Precise, but with Low Accuracy Accuracy is the degree of correctness while precision is the degree of reproducibility. Precise, but with Low Accuracy

16 Three Day Carbonate Petrophysics This three-day course is application-oriented, and designed for Petrophysicists, Engineers, Geologists and Team Leaders who are comfortable with integrated geology / routine & special core - log interpretation and require an understanding of the complexities of open-hole carbonate log analysis. The Course begins with a contrast of carbonates and sandstones, followed by reservoir classification according to the Lucia Petrophysical Classification System and capillary pressure. Individual logging tools (both routine and specialty) are introduced and carbonate responses are illustrated with actual data. Archie s exponents are discussed within the context of both his original measurements, and carbonate specific results. The concept of bulk volume water is introduced within the context of a Pickett Plot, and then related to Nuclear Magnetic Resonance and the combination of pore size and irreducible water saturation. Basic NMR, and carbonate specific NMR issues are introduced with laboratory measurements, numerical simulations and actual wireline data. In addition to NMR and other non-archie approaches,, the course will address laboratory determination of mineralogy (XRD/XRD/etc), porosity and CT Scan visualization, which play important supporting roles in carbonate evaluation. YOU WILL LEARN TO recognize the key distinctions between carbonates and sandstones within the context t of modern wireline measurements, and draw upon the strengths of specific tools / techniques to design a cross-discipline formation evaluation program that will best characterize a specific reservoir 2008 Robert E Ballay, LLC

17 Day 1 Start Stop Duration Topic Course Introduction & Overview Carbonate vs Sandstone (+GR Exercise) Capillary Pressure (+ Exercise) Break Lucia PP Classification (+ Exercise) Break Routine Sonic in Carbonate (+ Exercise) Lunch Density & Neutron in Carbonate (+ Exercise) Identification of Vuggy Porosity Break Light Hydrocarbon Issues (Wireline & LWD) Specialty Sonic Applications (+ Exercise) Break Rock Quality & Cutoffs Resistivity Measurements Summary Three Day Carbonate Petrophysics Day 2 Start Stop Duration Topic Archie s m Exponent (+ Exercise) Break Cement Exponent Variations and Pore Geometry "m" Estimates From Vuggy Porosity Ratio Break "m" Estimates From Vuggy Porosity Ratio Lunch Archie s n Exponent (+ Exercise) Low Resistivity Pay in Carbonates Break Pickett Plot The Non-Archie Toolbox & Fresh Water Challenge Break Basic NMR (+ Exercise) Summary 2008 Robert E Ballay, LLC The Devil s Promenade, SW Missouri

18 Day 3 Start Stop Duration Topic Carbonate NMR (+ Exercise) Break Core Calibrated Wireline "m" Estimates Dielectric Log Break Wireline "m" Estimates Compared to Core PNL Lunch PNL Pressure Profiles (+ Exercise) Break Image Logs (+ Exercise) CT Scan Break XRD/XRF/Mineralogy Phi / Mineralogy from Core Jerry Lucia: Here is how it works Summary Three Day Carbonate Petrophysics Now that s a Vug! Whispering Dell is one of seven sink holes at Ha Ha Tonka (SW Missouri) formed by the ceiling collapse of a large cave. The full page view is of the sink hole from the ridge above, and the insert shows the spring outlet (49 million gallons per day).

19 Client Considerations Carbonate Petrophysics My First, and Top Priority, is to ensure a-priori that the Course meets the Client s expectation. The focus of the Course is on carbonate matrix issues, and not fractured reservoirs. Course Content issues for Client Consideration are summarized following please read and consider carefully

20 Carbonate Petrophysics - Client Considerations Material is delivered to the Client in two forms The Manual, which plays the role of a text book The Presentation, which is drawn from the Manual, but expanded upon and optimized with respect to fonts and color codes Modules for the basic techniques typically begin with an introduction to the physics behind the actual measurements. This is a conscious and deliberate decision, based upon my experience as both a practicing petrophysicist and as an instructor. Many times I have discovered that even those with several years of experience, are not aware of some of the basic physical principles, and have thus compromised their use of the measurements. I realize, however, that there are audiences which are not interested in the Basic Physics and possibly not even in an Introduction ti to Basic Tools / Techniques. Please review the default set-up to ensure it satisfies your objectives. Continued in following exhibit

21 Carbonate Petrophysics - Client Considerations Not all modules (Field Studies, for example) in the Manual are covered in the presentation, but rather are included for future review and reference, when the basic tools and techniques have been developed in class. There may be audiences which are application oriented. Please review the default set-up to ensure it satisfies your objectives. Most of the modules have an Application Example included, which can be worked in class, or reviewed in class or left for the attendee to review in their leisure. I have found that t some folks like to have problems to work, and others don t care for them (and in fact disapprove of spending course time in this manner): I typically ask this very question in the Introduction Phase. It s preferable, however, to know the preference in advance. Key Issues are: Are they the kind of problems that you are looking for in the course? Shall they be reviewed or worked in class, or left for attendees to review at their leisure. e Please note that allowing time for problem solving will mean less time for technique presentation, as the time allocated in the course schedule will be adhered to in either situation. My First, and Top Priority, is to ensure a-priori that the Course meets the Client s expectation. Please work with me, in advance of scheduling the course, to ensure that every requirement has been considered.

22 R. E. (Gene) Ballay s 31 years in petrophysics include research and operations assignments in Houston (Shell Research), Texas; Anchorage (ARCO), Alaska; Dallas (ARCO Research), Texas; Jakarta (Huffco), Indonesia; Bakersfield (ARCO), California; and Dhahran, Saudi Arabia. His carbonate experience ranges from individual Niagaran reefs in Michigan to the Lisburne in Alaska to Ghawar, Saudi Arabia (the largest oilfield in the world). He holds a PhD in Theoretical Physics with double minors in Electrical Engineering & Mathematics, has taught physics in two universities, mentored Nationals in Indonesia and Saudi Arabia, published numerous technical articles and been designated co-inventor on both American and European patents. At retirement from the Saudi Arabian Oil Company he was the senior technical petrophysicist in the Reservoir Description Division and had represented petrophysics in three multi-discipline teams bringing on-line three (one clastic, two carbonate) multi-billion barrel increments. Subsequent to retirement from Saudi Aramco he established Robert E Ballay LLC, which provides physics - petrophysics p consulting services. Mississippian limestone Chattanooga shale He served in the U.S. Army as a Microwave Repairman and in the U.S. Navy as an Electronics Technician, and he is a USPA Parachutist and a PADI Dive Master.