Copyright 1999, Society of Petroleum Engineers Inc.

This paper was prepared for presentation at the 1999 SPE Annual Technical Conferenceand Exhibition held in Houston, Texas, 3–6 October 1999.

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AbstractVugs, which are defined as pores larger than adjacent grains,are common in many carbonate reservoirs. Such pores arenot always recognized by conventional wireline logs. Thepurpose of this study is to compare pore-size distributions inOligocene carbonates from China using core, boreholeimages, nuclear magnetic resonance, and capillary pressure.

The Kerr-McGee CFD2-1-2 well was drilled in theBohai Basin in China. The reservoir consists of dolomiticlimestones and fractured dolomite. The core (25 meters)was polished and inked with fluorescent paint, thenphotographed under black light to generate high-resolution,2-D black and white photos. Image analysis produceddetailed information about vug size and depth. Core imageswere then used to calibrate a Formation MicroImager (FMI)log, so that pixel counts of vugs from the FMI would matchcore observations.

Nuclear magnetic resonance (NMR) logs measure theT2 relaxation time, a parameter that is a function of poresize and reservoir fluid composition. Laboratory NMRmeasurements for six core plugs have been compared topore-size distributions from core images. Thesedistributions are comparable for high T2s (above 92milliseconds).Mercury intrusion capillary pressure (MICP) measurementsare used to determine pore-throat size distributions. Thesedistributions, which can be directly compared to NMR andimage analysis pore-size distributions, have very similarshapes.

The net result of this study is that a technique has beendeveloped to relate core-calibrated borehole images to NMR

and MICP data. This is an important step in the difficultprocess of understanding NMR log behavior in vuggycarbonate rocks.

IntroductionVuggy porosity is common in many carbonate reservoirs, butits presence or absence may not be detected by conventionalwireline logs because of their limited vertical resolution. Itis important to recognize vuggy porosity so that accuratereservoir properties can be derived resulting in less bypassedpay and higher proven reserves.

Choquette and Pray1 described vugs as equant poreswhich are large enough to be seen with the naked eye, but donot specifically conform in position, shape or boundary tograins within the host rock. Lucia2, 3 stated that vugs arepores that are significantly larger than framework grains.Because Lucia's definition can be better applied to boreholeimages, it is used in this study.

The Kerr-McGee CFD2-1-2 was drilled in the offshoreportion of the Bohai Basin in China (Figure 1). Thereservoir is composed of highly fractured dolomite,intraclastic molluscan grainstones-packstones and oncoliticrudstones of the Sha 3 member of the Oligocene ShahajieFormation4 (Figures 2, 3). Evaluation of the core and thinsections through the reservoir indicates that there isabundant interparticle porosity. All facies contain at leastsome vuggy porosity. Core and thin sections were evaluatedas part of a Master’s thesis by Ausbrooks.5 Maincontributions of this research were that: 1) four lithofacieswere identified in core and thin section, 2) vuggy porositywas imaged and quantified from both core photos and anFMI log and 3) NMR data from core plugs indicated thatthere were different pore sizes present, including vuggyporosity.

Quantifying Vugs from CoreSeveral studies have used core-photo image analysis andFormation Micro-Imager (FMI) logs to image vugs.6, 7, 8

Pixel counts of core photos have been used to calibrate anFMI log from the Kerr-McGee CFD2-1-2 well, the focus ofthis study.5

SPE 56506

Pore-Size Distributions in Vuggy Carbonates From Core Images, NMR, and CapillaryPressureRobin Ausbrooks, SPE and, Neil F. Hurley, SPE, Colorado School of Mines, Andrew May, SPE, and Douglas G. Neese,Kerr-McGee Corporation

2 R. L. AUSBROOKS, N. F. HURLEY, A. MAY, D. G. NEESE SPE 56506

Methods. Core was analyzed through the use of digitizedhigh-resolution core photos and pixel-counting techniques.7

The steps for preparing the core were:1) Polish to remove saw marks creating a smooth flat

surface. Polishing was done with a wet sanding-beltmachine and a 125-micrometer diamond abrasive.

2) Each piece of core was coated with water-soluble,block printing ink that was carefully applied with a softrubber roller so that it would only be deposited on therelatively higher core surface and not in the vugs. Twolayers of ink were applied: (a) a white undercoat to masklight and dark framework features, and (b) a fluorescent pinkouter coat which further masked all sedimentologicalfeatures and created an evenly colored surface. Thistechnique produces maximum contrast between matrix andvugs. The monochromatic paint color is easily filtered toproduce usable black and white images.

3) Level and photograph the core under ultravioletlight. Leveling is necessary so that the entire surface of thecore is kept at the same focal distance from the camera sothat the sizes and the shapes of the vugs are not distorted.This was accomplished by placing the pieces of core in awooden exposure box on a bed of black beans. Black beanswere chosen because they created a uniform darkbackground that could easily be removed after the negativeswere scanned.

The core was photographed with a modified MP-4+copy standard large-format camera. Illumination wasprovided by eight blacklight/bluelight fluorescent bulbspositioned around the core to produce uniform illuminationof the entire exposure box. These bulbs output onlyminimum amounts of visible light in the blue-yellowwavelengths which were screened out with a red filter(Kodak Wratten #29) placed in front of the lens duringexposure. Filtering prevented all visible light from reachingthe negatives, allowing only the wavelengths from thefluorescent ink to reach the negative. Exposure time wasvaried from 60 to 120 seconds and each print was checkedfor correct exposure and archived.

4) Digitally scan the negatives with an Agfa Duoscanflatbed scanner to produce a 256-level gray-scale file. Thescanner has an optical resolution of 1,000 pixels per inch.Software controls are used to maximize contrast betweenvugs and matrix. The final scanned image is a near-whiterock surface and near-black vug space with vug boundarypixels of intermediate color.

5) Reassemble core images on the computer foranalysis and extraction of vuggy porosity data. The imagesof each box of core are reassembled in Adobe Photoshopwhere the short columns in the scanned negatives arearranged into one long continuous column. Core pieces aredepth-matched to borehole images within Photoshop usingmulti-layered files in which each core piece is its own layer.Core pieces can be moved relative to each other to matchborehole images. At this point, edits were made to theimages of the core pieces so that all dark areas were trulyvugs and effects such as core plugs and scratches createdduring the polishing of friable core were removed. Photos

taken during the coring process were used to restore corepieces to proper depths within their boxes. There were gapsin the core due to zones of no recovery and whole coresamples being removed.

6) Image analysis processing of the depth-correctedcore was carried out using custom routines in NIH Image.Macros written by Robert Zimmermann in a modified Pascalprogramming language are applied to the core within NIHImage to allow it to be analyzed in batch processing moderather than as individual pieces. NIH Image has limited text-handling abilities and requires a large RAM allocationmaking on-screen navigation within it tedious and oftendifficult. The files that it generates cannot be fully displayedfor editing so output data is manipulated in Microsoft Excelbefore it is input into the Z&S Recall/Review softwarepackage.

Results. Data generated from these analyses are depth, porearea (pixels), and perimeter (pixels). Area % porosity iscomputed in 0.1-inch windows to emulate the 120 samples/ftrate of the FMI tool (Figure 4).

Quantifying Vugs from Borehole Images

Methods. The FMI log for the Kerr-McGee CFD2-12 wasimported into Z&S Recall Review for image analysis andquantification of vuggy porosity. The technique is describedin Hurley et al.6 The FMI log was depth shifted to matchother open-hole logs. The static image is used for analysisbecause the contrast setting has not been locally adjustedand most closely represents the raw data. The softwarecreates a histogram of all pixel gray shades. Thresholds areset and pixel counts are computed. The sum of the darkpixels over the total area is the percentage of vuggy porosityfrom the FMI log. Pixel counts were performed using thefollowing steps: 1) generate pixel counts using arbitrarythresholds such as 1%, 3% and 5% of the highestconductivity values at a sampling rate of 0.1 inch, the FMItool’s sampling rate 2) set a gamma ray cut-off to removeshales and replace pixel counts over these intervals so thatdark colored shales are not counted as porosity and 3)create frequency histograms of dark pixel counts forcomparison to frequency histograms from core pixel countsat the same depth.

Results. Overall the vuggy porosity logs generated fromcore photos and the FMI log identify the same vuggyintervals but porosity values differ somewhat (Figure 5).The core porosity log has higher values than the FMI log forseveral intervals, and lower values over other intervals. Onaverage, the curves match indicating that this calibration canbe employed in this setting.

NMR DataNMR data has been used successfully to evaluate sandstonereservoirs for many years but is only beginning to be appliedto carbonates.9, 10 Because these techniques were developedfor sandstones, there are uncertainties about their ability to

SPE 56506 PORE-SIZE DISTRIBUTION IN VUGGY CARBONATE FROM CORE IMAGES, NMR, AND CAPILLARY PRESSURE 3

measure the porosity contributed by larger pore-sizes invuggy carbonates. Relaxation times, measured in NMRanalysis, are related to pore-size distribution.

Methods. Laboratory NMR analyses are made on brine-saturated samples. These samples are subjected to apowerful magnetic field that causes all of the hydrogenprotons to orient themselves. A pulse is then transmittedcausing the oriented protons to tip 90 degrees. The amountof time for these protons to relax, or return to their originalposition, is called relaxation time and is a function of pore-size, connectivity and fluid composition.11 In the case ofthese analyses, 5,000 pulses were transmitted into eachsample at a rate of one every 320 microseconds. Responseswere recorded for a total time of 10,000 milliseconds.

There are two measurable values associated withhydrogen relaxation: T1, the longitudinal relaxation time andT2, the transverse relaxation time. Because T2 relaxation ismeasurable at logging speeds up to 600 feet per hour, it isapplied more often than T1, which takes longer to acquire.

NMR measurements were made on six core plugs(Table 1) ranging in depth from 3,420 to 3,437 meters andfrom 7-25% porosity. The frequency of responses at eachT2 time was measured and these are plotted on frequencyhistograms (Figure 6).

Results. NMR T2 distributions for all 6 samples show thatthere are several different pore sizes in the rocks. Allsamples contain a peak situated between 10 and 100milliseconds T2 time. This is inferred to be mostlyinterparticle porosity.10 There are also peaks at around1,000 milliseconds, which is interpreted to be vuggyporosity.12

MICP DataMercury capillary pressure data directly measure thepercentage of pore-space within a rock that can be filledwith a given fluid when a given amount of pressure isapplied. These data are used to calculate pore-throat sizeswhich in turn can be used to calculate T2 pore-sizedistributions for sandstone and carbonate reservoirs.9, 13

Hodgkins and Howard14 have recently shown a directcorrelation between NMR and MICP analyses for sandstonereservoirs.

Methods. MICP data in general, are commonly measuredby applying pressure to a core-plug to force mercury into allof the pore space. Air-saturated samples undergo a range ofincreasing pressure so that the cumulative amount ofmercury forced into the rock at each pressure step can berecorded. Initially, low pressure is applied and only porespaces connected by large pore throats are filled. Aspressure increases, mercury is forced into pore-spacesconnected by ever decreasing sizes of pore throats. In thisway, the range of pore-throat sizes is measured for eachsample.

For this study six samples were subjected to pressuresranging from 41 to 410,000 kPa and the cumulative amount

of mercury forced into the rock was measured at eachpressure step. Raw MICP data included pressure,cumulative percent saturation, pore-throat size, and aSwanson Parameter (Table 2). These data are used togenerate pore-throat-size distributions based on a proceduredescribed by Marschall et al.9

The amplitude values for the capillary pressure pore-size distributions must be calculated first. Cumulativesaturation values are subtracted from each other to arrive atincremental saturations that correspond to incrementalincreases in pressure (Table 2). For the second part of thisstep, the incremental values are summed and the percentagecontributed by each is calculated.

T2 values must be calculated for MICP pressures sothat a direct comparison can be made to the NMR T2distributions. This process begins with the relationship9:

1/T2 = ρ(V/S) (1)

in which T2, relaxation time, is in milliseconds; ρ, which isrelaxivity, is in µm/sec, and a pore volume to surface ratio,(V/S) is in µm.

Initially, pore radii are calculated from pressuredistributions with the Washburn equation:

r = 0.29σcosθ/Pc (2)

in which Pc is capillary pressure in kPa, r is pore-throatradius in µm, σ is interfacial tension in dynes/cm, and θ isthe contact angle (Table 2). Both of these parameters arebased on rock-type and these values were among the givendata for this study.

Pore-throat radii are converted to T2’s according to arelationship derived by Marschall et al. 9:

T2 = (1000r)/2ρe (3)

In this equation, T2 is in milliseconds, r is injection pore-radius in µm and ρe is the effective relaxivity in µm/sec.This equation is derived by substituting the surface tovolume relationship in Equation 1 into Equation 2. Thissubstitution establishes a relationship between pore volume-to-surface ratio, V/S, and r. The effective relaxivity variable(ρ) accounts for the fact that NMR measures pore-body size,whereas capillary pressure is a measure of pore-throat size.Effective relaxivities used to calculate T2’s for each samplewere assigned through trial and error (Table 2). Marschall etal.9 indicated that ρe for carbonate rocks ranges from 1-3,but values in this study ranged from 1.5 to 7.75.

Results. Calculated T2 values can be used to create a pore-size distribution from MICP data based on the percentage ofsaturated pore-space and the size of pore-throats in a rock(Figure 7). Although the MICP curves are based on thepore-throat size, and NMR is based on pore size, theeffective relaxivity (ρe) can be used to relate the two.

Pore-size distributions created from MICP dataindicate several pore-size populations with occasional high

4 R. L. AUSBROOKS, N. F. HURLEY, A. MAY, D. G. NEESE SPE 56506

frequencies of certain pore-sizes. Some of these very sharppeaks occur because the data has been plotted in its raw,unsmoothed form.

Comparison of Core, NMR, and MICP DataPore-size distributions for core, NMR and MICP data maybe compared by plotting them together on the same T2 axis.Chart 1 outlines the flow diagram necessary to create thisdisplay.

Step 1, plotting the NMR pore-size distributions, isthe basis for subsequent steps. NMR distributions arecreated by plotting the number of responses received foreach increment of time over a total time of 10,000milliseconds. Step 2, the calculation of percent saturationfor incremental pressure steps, and Step 3, calculating T2’sfrom pore throat radii,9 are described in the MICP Methodssection. These involve several spreadsheet operations asshown in Table 2. These steps create the MICP pore-sizedistribution and relate it to the NMR distribution.

Step 4 is the analysis of core-photo data. The steps toprocess the core and create the raw data, includingpercentage vuggy porosity and pore sizes for 0.1 inchintervals, are listed in the Methods section of QuantifyingVugs from Core. NMR and MICP core-plugs are locatedand six inches of data surrounding each is extracted formanipulation in a spreadsheet. Steps 5 and 6 are spreadsheetsteps and involve the creation of incremental porositydistributions from the core-photo pixel counts. In Step 5, thelogarithm of each vug area is calculated and vugs are sortedby this value to emulate size ranges outlined in the core-plugT2 data. In Step 6, the area contributed by each vug sizefraction is calculated and then divided by the total area of allvugs within the 6-inch interval to get the percentage of totalvuggy porosity contributed by each vug size range. Step 7 isthe plotting of all pore-size distributions together on thesame T2 chart. The NMR and MICP distributions have thesame x-axis scales and can be directly overlain. Core photodistributions represent only the higher T2 values and areoverlain on NMR and MICP starting at 92 milliseconds(Figures 8a-8f).

Chang et al10 recognized that CMR logs in vuggycarbonate reservoirs need to be calibrated to the reservoir toachieve accurate characterization of porosity and pore-sizedistributions. They experimented with both the CMR logand with samples from conventional NMR core analysis todetermine that 92 milliseconds was a suitable cutoffseparating movable water and bound water in Glorietta andClearfork reservoirs of west Texas. This cutoff may be toohigh to use in the Kerr-McGee CFD2-1-2 because it forcessome of the core-photo pore-size peaks to extend beyond theT2 range of the NMR and MICP data. However, forreference this cutoff is used to create all composite T2figures.

Discussion. T2 plots for mercury capillary pressure, NMRand core-photo pore-size distributions are very similar. TheT2 values created for the mercury capillary pressure dataallow the amplitudes to be compared directly to the NMR

pore-size distribution.13 All of the curves have several peaksindicating many pore-size populations within the rock. TheNMR data have been smoothed whereas the MICP data hasnot, which could account for some of the discrepancies inthe curves. Sample 4 has an area of the curve that does notreally match. There is a very high amplitude MICP peakbetween 500 and 1,000 milliseconds that does not appear onthe NMR curve. The MICP pore-size curve for Sample 13is different from the other samples in that it does not containdistinctive higher peaks. It was matched to the NMR curveby matching trends in each and the best possible fit wasachieved that way. The overall good match does indicatethat the equation developed by Marschall et al.9 works wellfor vuggy carbonate rocks.

The NMR and mercury capillary pressure T2distributions compare moderately well with pore-sizedistributions from core-photo analysis. The core-photodistributions begin at 92 milliseconds on the T2 axis andusually peak where the other curves peak. There areinstances in samples 2, 8, and 10 where the core-photocurves have peaks at longer T2 times than the other twocurves. The cut-off for vuggy porosity might be too high forthese samples.

ConclusionsThe Kerr-McGee CFD2-1-2 well encountered a carbonatereservoir composed of Oligocene grainstones and rudstones,and highly fractured Ordovician dolomite. The purpose ofthis study is to compare pore size distributions from NMRand mercury capillary pressure data and image analysis ofdetailed core-photos.

Pore-size distributions generated from these three datasets are comparable. Very similar trends are seen in all datafor each sample. All pore-size distributions indicate thepresence of several pore-size populations in all of the rocks.

Because trends seen on the NMR pore-sizedistributions are very similar to those seen in the MICP andcore-photo pore size distributions, we can conclude thatNMR analyses are measuring vugs in rock even up to thelargest pores. Because we have been able to relate boreholeimages to core-photo images, we feel we have developed atechnique to help understand NMR behavior in vuggycarbonates.

AcknowledgementsThis study presents some of the results of a researchconsortium entitled “Quantification of Vuggy Porosity inCarbonates Using Borehole Images and Core”. We wouldlike to acknowledge the following sponsors for their support:Anschutz Overseas Corporation, Chevron OverseasPetroleum, Conoco Inc., Gas Research Institute, Kerr-McGee Corporation, Marathon Oil Company, Shell/AlturaCorporation and Yates Petroleum. Z&S Consultants Inc.provided software and support. The U. S. Geological Surveyprovided core facilities. Robin Ausbrooks would like tospecifically acknowledge the support of the SPWLA grantsin aid and to thank Dan Hartmann and David Marschall fortheir expertise and input.

SPE 56506 PORE-SIZE DISTRIBUTION IN VUGGY CARBONATE FROM CORE IMAGES, NMR, AND CAPILLARY PRESSURE 5

References1. Choquette, P. W. and Pray, L. C.: “Geological

nomenclature and classification of porosity insedimentary carbonates,” AAPG Bulletin (1970) 54,207.

2. Lucia, F. J.: “Petrophysical parameters estimated fromvisual descriptions of carbonate rocks: a classification ofcarbonate pore space,” JPT (1983) 35 626.

2. Lucia, F. J.: “Rock-fabric/petrophysical classification ofcarbonate pore space for reservoir characterization,”AAPG Bulletin (1995) 79 1275.

4. Neese, D. G. and Jewell, G A.: “Developing anintegratedexploration strategy for complex carbonate reservoirs ina Tertiary wrench segmented basin: Bohai Bay, China,”paper A486, presented at 1998 AAPG AnnualConvention, Salt Lake City, Utah May 17-20.

5. Ausbrooks, R. L.: “Quantification of vuggy porosity andlithology using borehole images, core, and logs, BohaiBasin, Offshore China,” Colorado School of Mines,Unpublished Masters Thesis (1999) 164.

6. Newberry, B. M., Grace, L. M. and Stief, D. D.:“Analysisof a carbonate dual porosity system from boreholeelectronic images,” paper SPE-35158, in Permian BasinOil and Gas recovery Conference Proceeding, Midland,Texas (1996) 123.

7. Hurley, N. F., Zimmermann R. A. and Pantoja D.:“Quantification of vuggy porosity in a dolomitereservoir from borehole images and core, Dagger DrawField, New Mexico,” paper SPE 49323 presented at the1998 SPE Annual Technical Convention and ExhibitionNew Orleans, Louisiana, September 23-26.

8. Hurley, N. F., Pantoja D. and Zimmermann, R. A.:“Flow unit determination in a vuggy dolomite reservoir,Dagger Draw Field, New Mexico,” paper GGGpresented at the 1999 SPWLA 40th Annual LoggingSymposium Oslo, Norway, May 20-23.

9. Marschall, D., Gardner, J. S., Mardon, D. and Coates,G. R.: “Method for correlating NMR relaxometry andmercury injection data,” paper 9511 presented at the1995 SCA Conference.

10. Chang, Dohai, Vinegar, H., Morriss, C. and Straley, C.:“Effective porosity, producible fluid, and permeabilityin carbonates from NMR Logging,” The Log Analyst(1997) 38 No. 2, 60.

11. Kenyon, W. E.: “Nuclear magnetic resonance as apetrophysical measurement,” Nuclear Geophysics(1992) 6, 153.

12. Allen, D. S. et al.: “How to use borehole nuclearmagnetic resonance,” Oilfield Review (1997) 9, No. 2,p. 34.

13. Kleinberg, R. L., Farooqui, S. A. and Horsfield M. A..:“T1/T2 ratio and frequency dependence of NMRrelaxation in porous sedimentary rocks” Journal ofColloid and Interface Science (1993) 158, 195.

14. Hodgkins M. A. and Howard J. J.: “Application of

NMR logging to reservoir characterization of low-resistivity sands in the Gulf of Mexico,” AAPG Bulletin(1999) 83, No. 1, 114.

Chart 1: Steps for creation of composite pore-sizedistribution plots.

Step 4: Analyze Core Photos:Identify six-inch interval surrounding each NMR and MICPcore plug. Work with these pore-size distributions in aspreadsheet.

Step 7: Plot All Pore-Size Distributions:Place core-photo pore-size distributions on plots withMICP and NMR curves starting at 92 milliseconds T2.

Step 2: Calculate Amplitudes for MICP :Subtract the cumulative fractional saturation of MICP dataand calculate % of saturation contributed by eachincremental pressure increase.

Step 1: Create NMR Distributions:Plot NMR T2 amplitude curves.

Step 3: Calculate T2 for MICP Data:Vary ρe values (Equation 2) until peaks of NMR and MICPpore-size curves fall at the same T2 values. Plot MICPdata on T2 amplitude plots.

Step 5: Bin Vugs for Pore-Size Distribution:Take the logarithm of each vug area and sort toemulate size ranges in core-plug T2’s.

Step 6: Calculate % of Pore Space for each PoreSize: Sum the area of each size range and divide it by thetotal summed area for all ranges.

6 R. L. AUSBROOKS, N. F. HURLEY, A. MAY, D. G. NEESE SPE 56506

Table 1: Basic Rock Properties

SampleNumber

Depth (m) RockType

CorePorosity

pu

CorePermeability

md

GrainDensity

effective relaxivity(ρe) micrometers/sec

1 3420.05 Carbonate 0.245 12 2.82 3.52 3421.20 Carbonate 0.185 2.8 2.8 0.14 3422.90 Carbonate 0.245 29.1 2.8 1.758 3429.40 Carbonate 0.133 0.616 2.75 1.510 3431.40 Carbonate 0.211 2.57 2.78 1.513 3436.75 Carbonate 0.069 0.038 2.75 7.75

TABLE 2:MercuryInjection

GIVEN = Given data from lab analysis

CALC = Calculated values

Sample 13A B C D E F G H

Pressure Pore Bulk Calc Calc %Saturation

PoreThroat

Calc T2 Swanson

(kPa) Volume Volume Incremental FromIncremental

Radius, r ρe = 7.75 Parameter

Saturated(fraction)

Saturated(fraction)

Saturation Saturation (microns)

GIVEN GIVEN GIVEN CALC CALC GIVEN CALC GIVEN

* ** WashburnEquation

T2=(1000*r)/ (2*ρe)

20.616 0.000 0.000 0.000 0.000 35.671 2301.37845 0.0027.442 0.036 0.004 0.004 3.888 26.798 1728.92502 15.8137.854 0.078 0.009 0.005 4.536 19.428 1253.39191 24.8341.163 0.090 0.011 0.001 1.296 17.866 1152.61668 26.3551.437 0.124 0.015 0.004 3.672 14.297 922.402356 29.0658.332 0.141 0.017 0.002 1.944 12.607 813.371344 29.3472.053 0.169 0.020 0.003 3.024 10.206 658.480533 28.44

* Saturated bulk volume is cumulative downward. Incremental saturations are created from it by subtracting each number, subtracting each number from the number below it.

** Percent saturation is calculated by dividing each incremental saturation by the total bulk volume saturation and multiplying by 100 to get a percent value.

SPE 56506 PORE-SIZE DISTRIBUTION IN VUGGY CARBONATE FROM CORE IMAGES, NMR, AND CAPILLARY PRESSURE 7

Figure 1: Location of CFD2-1 field and Kerr-McGee’s CFD2-1-2 well.

Figure 2: Logs and cored interval of the Kerr-McGee CFD2-1-2 well.

0 10 20 kilometers

Hangu

Tangg

TanghaLeting

CFD2-1-2CFD2-1-1

CFD2-1-3CFD2-1-4 S. E. ASIA

8 R. L. AUSBROOKS, N. F. HURLEY, A. MAY, D. G. NEESE SPE 56506

Figure 3: Core description for the Kerr-McGee CFD2-1-2 well showing rock type, sedimentary features and dominantporosity type.

SPE 56506 PORE-SIZE DISTRIBUTION IN VUGGY CARBONATE FROM CORE IMAGES, NMR, AND CAPILLARY PRESSURE 9

Figure 4: Example of output data from analysis of core photos. The left track is a percentage of vuggy pore space, thecenter picture is the core in black and white, and the right track is vug size, in pixels with depth.

2 0 1 0 0 B la ck & W h ite C o re Im a g e 1 1 0 0 1 0 ,0 0 0% P o ro s ity (V ug g y) po re a re a s (p ixe ls )

10 R. L. AUSBROOKS, N. F. HURLEY, A. MAY, D. G. NEESE SPE 56506

Figure 5: Diagram of core-photo vuggy porosity and calibrated FMI vuggy porosity logs.

SPE 56506 PORE-SIZE DISTRIBUTION IN VUGGY CARBONATE FROM CORE IMAGES, NMR, AND CAPILLARY PRESSURE 11

Figure 6: Example of NMR T2 Distribution: Sample 1: 3,420.05 ft depth, core porosity: 25%, core permeability: 12millidarcies.

Figure 7: Example of MICP T2 Distribution: Sample 1: 3,420.05 ft depth, core porosity: 25%, core permeability: 12millidarcies. From Table 2, column D is plotted against column G.

Sam ple1: NMR T2 Distribution

0.000

0.500

1.000

1.500

2.000

2.500

3.000

0.100 1.000 10.000 100.000 1000.000 10000.000

T2 (milliseconds)

# of

Res

pons

es

Sample 1: MICP T2 Distributionrhoe = 3.5

0.000

2.000

4.000

6.000

8.000

10.000

12.000

0.100 1.000 10.000 100.000 1000.000 10000.000

T2 (milliseconds)

% In

crem

enta

l sat

urat

ion

12 R. L. AUSBROOKS, N. F. HURLEY, A. MAY, D. G. NEESE SPE 56506

T2 (milliseconds)

Figure 8a Composite of pore-size distributions for Sample 1. Solid = MICP, Long dash = NMR, Dot = core-photo pore-sizedistributions. MICP incremental saturation: 0-12%, NMR frequency: 0-3, core photo porosity 0-25%.

T2 (milliseconds)Figure 8b Composite of pore-size distributions for Sample 2. Solid = MICP, Long dash = NMR, Dot = core-photo pore-sizedistributions. MICP incremental saturation: 0-12%, NMR frequency: 0-3, core photo porosity 0-25%.

Sample 1: 3,420.05 mρe = 3.5 micrometers/sec

0.1 1.0 10 100 1,000 10,000

Sample 2: 3,421.20 mρe = .1 micrometers/sec

0.1 1.0 10 100 1,000 10,000

MICPNMRCore

MICPNMRCore

SPE 56506 PORE-SIZE DISTRIBUTION IN VUGGY CARBONATE FROM CORE IMAGES, NMR, AND CAPILLARY PRESSURE 13

T2 (milliseconds)

Figure 8c Composite of pore-size distributions for Sample 4. Solid = MICP, Long dash = NMR, Dot = core-photo pore-sizedistributions. . MICP incremental saturation: 0-12%, NMR frequency: 0-3, core photo porosity 0-25%.

T2 (milliseconds)Figure 8d Composite of pore-size distributions for Sample 8. Solid = MICP, Long dash = NMR, Dot = core-photo pore-sizedistributions. MICP incremental saturation: 0-12%, NMR frequency: 0-3, core photo porosity 0-25%.

Sample 4: 3,422.90 mρe = 1.75

0.1 1.0 10 100 1,000 10,000

Sample 8: 3,429.40 mρe = 1.5 micrometers/sec

0.1 1.0 10 100 1,000 10,000

MICPNMRCore

MICPNMRCore

14 R. L. AUSBROOKS, N. F. HURLEY, A. MAY, D. G. NEESE SPE 56506

T2 (milliseconds)

Figure 8e Composite of pore-size distributions for Sample 10. Solid = MICP, Long dash = NMR, Dot = core-photo pore-size distributions. MICP incremental saturation: 0-12%, NMR frequency: 0-3, core photo porosity 0-25%.

T2 (milliseconds)

Figure 8f Composite of pore-size distributions for Sample 13. Solid = MICP, Long dash = NMR, Dot = core-photo pore-size distributions. MICP incremental saturation: 0-12%, NMR frequency: 0-3, core photo porosity 0-25%.

Sample 10: 3,431.40 mρe = 1.5

0.1 1.0 10 100 1,000 10,000

Sample 13: 3,436.71 mρe = 7.75

0.1 1.0 10 100 1,000 10,000

MICPNMRCore

MICPNMRCore