Residual HC Saturation in the Maui Field - SPE, 2001

Copyright 2001, Society of Petroleum Engineers Inc.

This paper was prepared for presentation at the SPE Asia Pacific Oil and Gas Conference andExhibition held in Jakarta, Indonesia, 1719 April 2001.

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AbstractResidual gas and oil saturations and relative permeabilitieshave been quantified in the Maui Field. Additional SpecialCore Analysis (SCAL) laboratory data was acquired usingdecane/brine and oil/brine centrifuge experiments. Suchmeasurements are considered most representative of waterinflux into gas and oil reservoirs respectively. In the case ofoil, ageing of the samples to restore wettability is shown to beessential. Relative permeability curves were obtained byhistory matching the raw experimental production data vianumerical simulation. This process corrects for experimentalartefacts and limitations, resulting in a significant reduction inresidual hydrocarbon saturations compared to typicalanalytical interpretations. A correlation using a form originallyproposed by Land has been used to relate the residualhydrocarbon saturations to the initial water saturations. In-situfield measurements of hydrocarbon saturations using pulsedneutron logs in water-flooded zones are shown to support theSCAL data.

The work described represents the state-of-the-art inquantification of residual hydrocarbons. In particular, thecombination of the sampling methodology, the experimentdesign, the advanced numerical interpretation and the in-situmeasurements is material previously unpublished in technicalliterature. The results are significant in that they show lowerresidual saturations than commonly expected, while adding tothe limited published data on residual hydrocarbons. Use oflower residual hydrocarbon saturations together with theappropriate relative permeabilities in reservoir simulation hasresulted in improved reservoir history matches and has had apositive influence on Maui Field reserves. Application of thesestate-of-the-art techniques to other water-drive fields is likelyto have a similar impact.

IntroductionAn understanding of the relative permeability of hydrocarbonsand water is essential for reservoir simulation. The remaininghydrocarbon saturation after water flood and hence theultimate recovery (UR) is strongly determined by the tail endshape of the imbibition relative permeability curve, close tothe residual hydrocarbon saturation.

This paper reports the results of extensive SCAL studies tobetter quantify relative permeabilities, including residualhydrocarbon saturations, in most of the gas and oil reservoirsof the Maui Field.

The Maui gas and oil field, off the Taranaki coast, NewZealand, was discovered in 1969. Figure 1 gives an overviewof the various gas/condensate and oil sands in the Maui-A and-B area. The Maui-A C and D gas sands were brought onstream in 1979 via a single production platform, MPA. In1992 a second production platform, MPB, was installed toproduce gas/condensate from the B area. In 1993 the Maui-BC and Upper D gas sands were brought on stream via thissecond platform tied back to the MPA platform. Also in 1993an oil accumulation was discovered in the B F sandsunderlying the C and Upper D gas reservoirs and the Lower Doil reservoirs. The Maui-B Lower D and F oil sands have beenproducing since September 1996 via the FPSO Whakaaropaiconnected to MPB.

The residual gas and oil saturations previously used forMaui reservoir modelling are high compared with recent state-of-the-art SCAL studies carried out on sandstone reservoirsfrom various fields around the world1. In these recent studies,a systematic reduction in residual hydrocarbon saturations, incombination with higher Corey exponents, is observed.

There are two reasons that could explain the likely too-high estimates for the previous residual hydrocarbon saturationdata.

Firstly, the previous experimental gas and oil data wereinterpreted using conventional analytical methods in which, bydefinition, it is assumed that the capillary pressure isnegligible. Recent research has shown that the underestimationof capillary end-effects in the analytical interpretation methodsmay lead to residual hydrocarbon saturation values that are 10-15% too high1. In the SCAL studies reported in this papercentrifuge data has therefore been acquired to allowinterpretation by numerical simulation of the relative

SPE 68741

Residual Hydrocarbon Saturations in the Maui FieldM.H.W. Verbruggen, SPE, Shell Todd Oil Services Ltd., and S.J. Adams, SPE, Petrophysical Solutionz Limited

2 M.H.W. VERBRUGGEN, S.J. ADAMS SPE 68741

permeability experiments. During previous SCAL studiesinsufficient data were recorded to allow numerical modelling.

Secondly, the oil measurements were performed on corematerial that was left water-wet after cleaning, which is nowbelieved to be a questionable method and might be the causeof the very high Corey exponents observed and possiblyaccount for the high Sor values. It is likely that the old data isnot representative of the oil reservoirs since asphaltenes arepresent in Maui oil and can have a large impact onwettability2.

Experimental ProgramExperiments have been carried out to determine saturationfunctions (capillary pressure and relative permeability)characteristic for the Maui-A and -B C gas sands3, the B UpperD gas sands and the B Lower D oil sands4. The basic SCALprogram to determine saturation functions for oil/brine andgas/brine systems was outlined as follows: Acquire sufficient measurements to ensure representative

coverage (facies, porosity, permeability). Determine impact of ageing on residual oil saturation and

oil/water relative permeability. Measure imbibition and 2nd drainage Pc curves for use in

simulation of the relative permeability raw data. Quantify repeatability of the experiments. Output representative saturation functions.

For the oil/brine experiments, to restore wettability to thecleaned water-wet core samples, all plugs were batch aged inan oven at appropriate reservoir temperature and pressure.Two spare samples were set up with the rest of the SCALsamples and permeability to oil measured every few days. Thepermeability to oil stabilised after approximately 24 days,indicating wettability had been restored.

To provide measurements applicable to a gas/watersystem, light-oil (decane) and brine have been used as modelliquids in order to overcome problems with the very lowviscosity and high compressibility of gas. The decane/brinecore samples were not aged as wettability is not an issue forgas displacements. Gas (i.e. decane in the SCAL experiments)is the non-wetting phase w.r.t. the wetting phase, which can beeither water or oil. In this case water is the wetting phase, butthe results are equally applicable to gas/oil displacement.

Measurements were made using both centrifuge andsteady-state techniques. Details of these methods have alreadybeen published5,6 and will not be repeated here, but a summaryis presented below.

Steady-State Experiment. In the steady-state technique, twoimmiscible fluids are injected simultaneously at constant ratesinto a core plug at a given fractional flow ratio. Measurementsare made at each fractional flow until steady-state conditionsare reached. A number of different fractional flows are usedfrom 100% hydrocarbon to 100% water flow. Pressure drop,saturation and flow rates are monitored. Relativepermeabilities can then be calculated using Darcys law.

The technique cannot determine residual saturations withhigh precision within a reasonable measurement time becauseof the low relative permeabilities when approaching residualsaturations. Estimates of Shr made using the steady-statetechnique should be considered as maximum values.

Centrifuge Experiment. During a centrifuge experiment, acore plug is saturated with one phase and spun round, at afixed centrifugal acceleration, in a core holder filled with theother phase. The production of the one phase, expelled fromthe core plug by the centrifugal force, is measured as afunction of time. In an imbibition experiment, hydrocarbon isexpelled from the plug and the hydrocarbon relativepermeability krh can be determined for decreasing hydrocarbonsaturation. In a drainage experiment, water is expelled and thewater relative permeability krw can be determined fordecreasing water saturation.

Multi-speed centrifuge experiments are carried out at seriesof fixed centrifugal accelerations and are used to determinecapillary pressure. Also relative permeability of the expelledphase can in principle be determined from a multi-speedexperiment.

Quality ControlDean-Stark checks. For the Maui-B Upper D decane/brineand Lower D oil/brine experiments, a comparison was madebetween the residual values reported for the last cycle on eachexperiment, and the saturations measured using Dean-Starkextraction. On average the difference was 2 - 3%, althoughsome plugs exhibited 5 - 10% difference. This informationwas considered when determining the final residualhydrocarbon and Corey exponent values. For the C sandsdecane/brine experiments these checks were not carried out.

Bond number. De-saturation effects can cause changes incapillary pressure and relative permeability at high flowrateand/or low interfacial tension, which (usually) do not occurunder normal field conditions. To avoid these effects, thecritical Bond number (ratio between gravitational and capillaryforces) should not exceed the value of 10-5. This Bond numberrequirement implies an upper limit for the centrifugalacceleration. The experiments carried out at a Bond numbermuch higher than 10-5 were discarded.

Repeatability. Seven of the oil/brine samples were re-run tocheck the experimental repeatability. The majority of samplesrepeated well. Repeat experiments typically showed amaximum difference in residual oil saturation of about 3%.

InterpretationCentrifuge Analytical Interpretation. The analyticalinterpretation of raw centrifuge data is an establishedtechnique5,6 and will not be presented here.

Centrifuge Numerical Interpretation. The centrifugetechnique provides information on capillary pressure andrelative permeability (for expelled phase only). It is impossible

SPE 68741 RESIDUAL HYDROCARBON SATURATIONS IN THE MAUI FIELD 3

to fully separate the two rock properties in practise andnumerical simulation is the appropriate tool to unravel theseparate role of capillary pressure and relative permeability inthe centrifuge data. In addition, a number of experimentalfactors influence the data as well.

A finite mobility of the invading phase affects earlyproduction in particular and results in errors in the analyticallyderived relative permeability at high saturations of theexpelled phase. With numerical interpretation this error isavoided. Another experimental factor is the start-up time ofthe centrifuge, which causes a delay in production and thusalso results in an error in the analytically derived relativepermeability at high saturations of the expelled phase. Thisstart-up effect is also corrected for by numerical interpretation.Yet another experimental factor that can only be corrected forby numerical interpretation, is a non-constant centrifugalacceleration along the sample.

Experiment Simulation. The MoReS (Shell proprietary)reservoir simulator7 has been used to determine relativepermeability from raw production data by history matching theexperimental data.

A typical example (Maui-B Lower D oil sands) of a SCALinterpretation by numerical interpretation is given in Figures 2and 3. In Figure 2 the match on the measured averagesaturation in the sample as a function of time is shown.Figure 3 shows the saturation distribution in the sample at theend of the experiment, illustrating a large capillary hold-upeffect, which would introduce a significant error if theexperiment was interpreted analytically instead of numerically.

In the fitting process, the Corey exponents of both phasesand the residual saturation have been allowed to vary withinrealistic limits. The end-point relative permeabilities havebeen kept fixed at the measured values whenever possible.Only when a reasonable match could not be obtained werethese end-point values allowed to vary.

Numerical Results. Figure 4 shows a typical example ofthe resulting relative permeabilities for an oil/brine imbibitionexperiment (same as in Figures 2 and 3) as interpretedanalytically by the contractor, as interpreted analytically withthe Hagoort method6 and as interpreted numerically. The twoanalytical methods agree very well in general, except for theend-point relative permeability, (in the contractors analyticalmethod, the end-point has been shifted to the measured value).

The imbibition history matches are in general of a betterquality than the 2nd drainage fits. For all 2nd drainageexperiments the end-point relative permeability value had tobe varied, whereas only a few of the imbibition experimentshad to have end-points varied.

Steady-State Interpretation. Provided the flow rates are highenough to avoid large end-effects but not so high that thecritical Bond number is exceeded, the steady-state experimentscan be simply analytically interpreted.

ResultsNote that unless stated otherwise results are given for in-situconditions. Also note that unless stated otherwise, Shr is

defined as the hydrocarbon saturation at which thehydrocarbon relative permeability equals 10-5. This is done tobe able to directly compare analytically with numericallyinterpreted Shrs. When using e.g. the Corey function format inreservoir simulation, these Shrs need to be converted though totrue Shrs, i.e. with hydrocarbon relative permeabilityequalling zero.

In the averaging of results, dubious results have been leftout, i.e. experiments with poor agreement with Dean-Starkvalues, experiments with a poor history match andexperiments with a too high Bond number. A summary of themain Maui SCAL results is provided in Table 1.

Oil/water capillary pressure and relative permeability bycentrifuge. Fourteen Maui-B Lower D samples weremeasured with the centrifuge, all samples being aged (i.e. theimbibition and 2nd drainage cycles were carried out afterageing). Multi-speed centrifuge runs were first run todetermine capillary pressure curves. The full Pc curves wereused as input in numerical simulation of the relativepermeability raw data. These Pc curves also offer anindependent estimation of residual oil saturation after theimbibition cycle. Then single-speed runs were carried out todetermine kro and krw curves. This relative permeability data isthe most accurate for residual oil saturation determination.

A comparison of analytically interpreted latest versusprevious residual oil saturations for the Lower D sands isshown in Figure 5. There is a large reduction in Sor (averageSor going down with 19% from 36% to 17%) that can beattributed to the latest dataset being aged. This clearly showsthe critical importance of core analysis being made onrepresentative (i.e. aged) core plugs.

Figure 6 compares the analytically and numericallyinterpreted residual oil saturations from the latest relativepermeability centrifuge experiments. Analytical interpretationof the imbition experiments, as mentioned before, results in anaverage Sor of 17%, whereas numerical interpretation results inan average of 11%, clearly illustrating the importance ofnumerical interpretation. The various reservoir units within theMaui-B Lower D oil sands show no distinct behaviour.

In Figure 7 the good simulation results are plottedtogether with the residual oil saturations derived from thecapillary pressure imbibition cycle. Highlighted are the datapoints that were excluded from either the low, base or high Sorregressions. For these regressions a Land correlation8 betweenSor and initial water saturation has been used. The Landcorrelation (characterised by the Land factor, C) is defined as:

1)1()1(+-

-=

wi

wihr SC

SS

For input into reservoir simulation of the Maui-B Lower Doil sands all parameters are taken from the imbibitionexperiments since this is most representative for the actualhydrocarbon/water displacement process in the field. TheCorey exponent for water, however, is taken from the 2nd

drainage experiments, since interpretation of these is much


more sensitive to this parameter than interpretation of theimbition experiments.

Oil/water relative permeability by steady-state. Steady-stateexperiments are time-consuming and expensive, so only threeMaui-B Lower D plugs were chosen.

The mid-saturation range of the relative permeability curvecannot be estimated accurately from centrifuge experiments ifinterpreted analytically, hence steady-state experiments usedto be recommended for this saturation range. However,numerical interpretation of the centrifuge experiments shouldbe able to largely remove the inaccuracy in the mid-saturationrange. Another objective of the steady-state experimentstherefore was to confirm the numerically interpreted centrifugeexperiment values for this range. Steady-state measurementsshould not be used when determining saturation end-points.The steady-state data is therefore not used in averagingresidual oil saturations.

Figures 8 and 9 compare the (analytically interpreted)steady-state and (numerically interpreted) centrifuge relativepermeabilities of the Maui-B Lower D core plugs for oil/brineimbibition and 2nd drainage respectively. Figure 8 shows agood agreement between the two measurement techniques,thus illustrating that numerical interpretation of the centrifugeexperiments properly corrects for experimental artefacts in themid-saturation range in case of oil/brine imbibition.

Figure 9 shows that the agreement between the two SCALtechniques for 2nd drainage is not as good as for the imbibitionexperiments. This may be partly due to spontaneous drainageeffects. However, the 2nd drainage data are only used todetermine the average water Corey exponent and the shapes ofthe steady-state and centrifuge curves are in reasonableagreement, so numerical interpretation of the centrifugeexperiments is also a sufficient correction for 2nd drainage.

Gas/water capillary pressure and relative permeability bycentrifuge. Six Maui-B Upper D and fourteen C core plugswere measured with the centrifuge. For the C sands samples,multi-speed centrifuge runs were first run to determine Pccurves, whereas for the Maui-B Upper D samples a previouslyestablished correlation between porosity and capillary pressurewas used. The full Pc curves were used as input in numericalsimulation of the relative permeability data. Single-speed runswere carried out to determine krg and krw curves. This relativepermeability data is the most accurate for residual gassaturation determination.

For the Upper D samples, numerical interpretation reducesthe average Sgr from 19.7% to 17.4% compared to the averagefrom analytical interpretation. For the C samples, numericalinterpretation leads to a reduction in average Sgr from 24.1% to19.4% compared to analytical interpretation.

Figures 10 and 11 show both the analytical andnumerically interpreted residual gas saturations from therelative permeability experiments for the C and Upper Dsamples respectively. Also the results of a least squares Landcorrelation fit versus initial water saturation are shown forboth sands. The various reservoir units within both the C sands

and the Upper D sands show no distinct behaviour. Noted onthese figures are the numerically simulated samples that hadpoor fits and were therefore not used in deriving averages.

For the Upper D sands, in Figure 12, the "good" simulationresults are plotted with the residual gas saturations derivedanalytically from previous data. This previous data has beencorrected by decreasing the Sgr with 2.3% (as suggested bynumerical interpretation). Highlighted are the data points thatwere excluded from either the low, base or high Landcorrelation regressions. The results of the least squares Landcorrelation fit versus initial water saturation are shown in thesame figure. The three cases reasonably cover all of theprevious and current data.

A somewhat different uncertainty band estimation has beenused for the C sands. Since the successfully simulatedexperiments for the C sands are only few in number (10), itwas decided to use analytically interpreted results of bothprevious and current experimens (29 samples in total) todetermine the uncertainty range of the Land factor in the Csands Sgr relationship. The uncertainty range from theanalytically derived Sgr values is assumed to be proportionallyapplicable to the Sgr values derived by simulation. For thesimulated data, the base case Land factor is 3.68,corresponding to an Sgr value of 19.7% for the average Swi of27.8%. The resulting low and high case Land factors are 4.77and 2.30 respectively, resulting in Sgr values of 16.2% and27.1% respectively for the same average Swi. Figure 13 showsthe derived relationships together with the simulated data.

For input into reservoir simulation of the C gas sands, allparameters are taken from the imbibition experiments exceptfor the Corey exponent for water, which is taken from the 2nd

drainage experiments. For the Upper D gas sands though, allparameters are taken from the imbibition experiments,including the water Corey exponent, as the 2nd drainageexperiments contain too few good results.

In-situ residual gas saturations. Pulsed-neutron logs havebeen acquired at frequent intervals in several Maui A wellssince the early 1980s. Comparison between the logs fromdifferent times allows changes in gas and water saturationsbehind casing to be identified. Pulsed-neutron logs used in thistime-lapse mode provide the only in-situ measurements ofgas saturation changes in the Maui Field. These logs have beenanalysed to determine residual gas saturations seen in the field.

Evaluation of the pulsed-neutron logs was carried out insix Maui wells with baseline data. Processing of the logsincluded depth-matching and averaging of passes,normalisation across water and gas bearing intervals expectedto be unchanged and intervals of unchanged borehole content.Water and gas properties were determined from literature9,10.

Changes in water saturations were estimated usingcomparisons of logs taken in the same wells at different timesi.e. in time-lapse mode. The differences between thenormalised logs have been used to estimate an uncertainty inwater saturation changes of 8% at porosities of 20%. Lowerporosities have a higher uncertainty, owing to the smaller


changes in pulsed-neutron response and to the higher relativeuncertainty in the porosity.

A plot of the most recent C sands gas saturations from eachwell in an initial water versus current gas saturation format(Figure 14) allows comparison with the core analysis derivedresidual gas saturation relationships. Since not all zonescovered by the pulsed-neutron logs are fully water swept,Figure 14 should be interpreted by looking at the lowerenvelope of the data for in-situ residual gas saturations. It isapparent that the Sgr estimates from the laboratorymeasurements do not conflict with the in-situ data, especiallywhen the log uncertainty is considered. It is also possible thatthe log data is suggesting that the low case Sgr Landcorrelation may eventually be reached in-situ.

Conclusions1. Numerical simulation of core experiments is critical in

determining accurate residual saturations and Coreyexponents.

2. Oil/water relative permeability curves, and associatedresidual oil saturation values, are substantially affected bythe wettability of the core plug. Core analysis for oilreservoirs should therefore be carried out on plugs that areaged at reservoir temperature and pressure.

3. Residual hydrocarbon saturation in the Maui Field isdependent on initial hydrocarbon saturation and can bedescribed with a Land correlation. Relationshipsrepresenting the high, expectation and low case residualhydrocarbon saturations have been derived directly fromcore data for most of the Maui gas and oil sands.

4. Re-analysis and re-calibration of pulsed-neutron logsavailable in Maui-A has enabled in-situ estimates ofresidual gas saturations to be made. These measurementssupport the laboratory estimates of Sgr.

5. Use of lower residual oil saturations together with theappropriate relative permeabilities in reservoir simulationhas significantly improved the history matches in theMaui-B oil sands. This has also resulted in increasedreserves in the Maui-B oil sands.

NomenclatureC =Land factorkr =relative permeabilityn =Corey exponent

Pc =capillary pressure, m/Lt2, kPa

S =saturation

UR =ultimate recovery

Subscriptsg =gash =hydrocarboni =initialo =oilr =residualw=water

AcknowledgementsThe authors would like to thank Shell Todd Oil Services andthe Maui Joint Venture Partners (Fletcher Challenge Energy,Shell Petroleum Mining Co. and Todd Petroleum Mining Co.)for giving permission for this paper to be presented on theirbehalf. Recognition is given to Shell Technology E&P inRijswijk, The Netherlands, for their work in this area.

References 1 Kokkedee, W., Boom, W., Frens, A.M. and Maas, J.G.: Improved

Special Core Analysis: Scope for a Reduced Residual OilSaturation, Proceedings from the 1996 InternationalSymposium of the Society of Core Analysts, SCA 9601, (1996).

2 Anderson, W.G.: Wettability Literature Survey - Part 4: Effects ofWettability on Capillary Pressure, JPT, (Oct. 1987) 1283.

3 Adams, S.J., Farmer, R.G., Hawton, D. and Seybold, O.:Laboratory and In-Situ Determination of Residual GasSaturations in Maui, 2000 New Zealand Petroleum ConferenceProceedings, Christchurch, Mar. 19-22.

4 Verbruggen, M.H.W., Farmer, R.G. and Adams, S.J.: State-of-the-art SCAL Experiments and Interpretation, 2000 New ZealandPetroleum Conference Proceedings, Christchurch, Mar. 19-22.

5 Hassler, G.L., and Brunner, E.: Measurement of Capillary Pressurein Small Core Samples, Petroleum Technology, (Mar. 1945).

6 Hagoort, J.: Oil Recovery by Gravity Drainage, SPE 7424, (Jun.1980).

7 Regtien, J.M.M., Por, G.J.A., van Stiphout, M.T. and van der Vlugt,F.F.: Interactive Reservoir Simulation, SPE 29146, (Feb.1995).

8 Land, C.S.: Calculation of Imbibition Relative Permeability forTwo- and Three-Phase Flow from Rock Properties, SPE 1942,Transactions Volume 243, (Jun. 1968).

9 Western Atlas International: Atlas Wireline Services LogInterpretation Charts, (1988).

10 Schlumberger: Log Interpretation Charts, SchlumbergerEducational Services, (1991).

TABLE 1 SUMMARY OF INTERPRETED SCAL RESULTS (for in-situ conditions)

Maui Reservoir Hydrocarbon Parameter Low Case Base Case High CaseB C sands Gas Land correlation factor (C) 4.77 3.68 2.30

Corey exponent hydrocarbon 4.2Corey exponent water 5.4End-point kr hydrocarbon 0.94End-point kr water 0.95

B Upper D sands Gas Land correlation factor (C) 4.68 3.63 3.32Corey exponent hydrocarbon 4.7Corey exponent water 2.3End-point kr hydrocarbon 0.92End-point kr water 0.74

B Lower D sands Oil Land correlation factor (C) 10.1 9.07 6.89Corey exponent hydrocarbon 4.6Corey exponent water 2.9End-point kr hydrocarbon 0.74End-point kr water 0.47

Fig. 1: Cross-section of Maui Field.


Sample: #202 (imbibition)

0

0.2

0.4

0.6

0.8

1

1E-4 1E-3 1E-2 1E-1 1E+0 1E+1 1E+2

Time [hour]

Sw

Simulated saturation

Experimental saturation

Fig. 2: Typical example of history match on measured averagesaturation in sample (Lower D sands sample #202, centrifugeoil/water imbibition experiment, ambient conditions).

Sample: #202 (imbibition)

-6

-5

-4

-3

-2

0 0.2 0.4 0.6 0.8 1Sw

length

alo

ng s

am

ple

[c

m]

Saturation profile @end of experiment

Capillaryhold-up

Water inflow face

Outflow face

Fig. 3: Typical example of simulated saturation distribution insample at end of experiment sample (Lower D sands sample #202,centrifuge oil/water imbibition experiment, ambient conditions).

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

0 0.2 0.4 0.6 0.8 1Sw

k r

kro, simulation

kro, Hagoort analytical

kro, contractor analytical

krw, simulation

krw, Hagoort analytical

krw, contractor analytical

Fig. 4: Typical example of oil/water relative permeabilities asderived analytically and by numerical simulation (Lower D sandssample #202, centrifuge oil/water experiments, ambientconditions).

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0 0.1 0.2 0.3 0.4 0.5Swi

Sor

Previous data (unaged)

From centrifuge Pc (aged)

From centrifuge kr (aged), analytical

Average previous (unaged) Sor = 36%

Average centrifuge (aged) Sor = 17%

Fig. 5: Analytically interpreted Lower D sands residual oilsaturations comparison between previous (unaged) data andlatest (aged) data.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.0 0.1 0.2 0.3 0.4 0.5 0.6Swi

Sor

Before simulation

After simulation

Poor simulation

Poor simulation

Poor simulation

Fig. 6: Comparison of analytically and numerically interpretedLower D sands residual oil saturations.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.1 0.2 0.3 0.4 0.5

Swi

Sor

From centrifuge kr, after simulation

From centrifuge Pc

Land P85 - 6.89

Land P50 - 9.07

Land P15 - 10.1

Low permeability (mobility) probably not reached SorExcluded from base & low Sor fits

High Bond numbers . Excludedfrom base & high Sor fits

Excluded from base & low Sor fits (disagree with main trend)

Excluded from high Sor fits (disagrees with main trend)

Fig. 7: Lower D sands residual oil saturation correlated with initialwater saturation.


1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

0 0.2 0.4 0.6 0.8 1

Sw

k ro Steady-State #201

Steady-State #42

Steady-State #64

Centrifuge #49

Centrifuge #52

Centrifuge #52 Rerun

Centrifuge #59

Centrifuge #66

Centrifuge #92

Centrifuge #136


Centrifuge #147


Centrifuge #202


Centrifuge #219

Centrifuge #221

Centrifuge #230

Centrifuge #240

Fig. 8: Lower D sands oil relative permeability (imbibition) fromcentrifuge and steady-state measurements (ambient conditions,steady-state with markers).

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

0 0.2 0.4 0.6 0.8 1

Sw

k rw

Steady-State #01Steady-State #42Steady-State #64Centrifuge #49Centrifuge #52Centrifuge #52 RerunCentrifuge #59Centrifuge #66Centrifuge #92Centrifuge #136Centrifuge #136 RerunCentrifuge #147Centrifuge #147 RerunCentrifuge #202Centrifuge #202 RerunCentrifuge #219Centrifuge #221Centrifuge #230Centrifuge #240

Fig. 9: Lower D sands water relative permeability (2nd drainage)from centrifuge and steady-state measurements (ambientconditions, steady-state with markers).

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Swi

Sgr

Before simulationAfter simulation

Fig. 10: Comparison of analytically and numerically interpretedUpper D sands residual gas saturations.


0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.2 0.4 0.6 0.8 1.0

Swi

Sgr

Before simulation

Land P50 before simulation

After simulation

Land P50 after simulation

Excluded fromLand fit

Fig. 11: Comparison of analytically and numerically interpreted Csands residual gas saturations.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.1 0.2 0.3 0.4 0.5 0.6Swi

Sgr

After simulation

Previous centrifuge kr data, corrected

From centrifuge Pc

Land P85 - 3.32

Land P50 - 3.63

Land P15 - 4.68

Excluded from high& base Sgr fits

Excluded from low & base Sgr fits

Fig. 12: Upper D sands residual gas saturation correlated withinitial water saturation.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Swi

Sgr

After simulation

Land P85 - 2.30

Land P50 - 3.68

Land P15 - 4.77

Excluded fromLand fit

Fig. 13: C sands residual gas saturation correlated with initialwater saturation.

0.5

0.6

0.7

0.8

0.9

1.0

0 0.2 0.4 0.6 0.8 1

Swi

Sw P

NC

MA-01MA-02MA-07MA-08MA-10MA-12P15P50P85

Fig. 14: Gas saturations measured (pulsed neutron logs) in Maui Awells.

Documents

Residual HC Saturation in the Maui Field - SPE, 2001