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SPEsQck3tuurPebakturllmxnem3

SF% 22357

Defining Data Requirements for a Simulation StudyA,K.Dandana, F!.E3.Alston,and FtW. Braun,Texaco Inc.

SPE Members

Copyright 1992, Soclery of Pts!roleum2n@neers, Inc.

This paper was prepared for presmtahon a! the SPE internationalMeeting on petroleum En9meerin9 held in g~limachina,?~-zpMarCh1982.

This paper was aelectod Ior presentationby an SPE Program Committee followingrovlew of informationcontained in an absfracl eubmittadby the author(a).C4nlents o! the paper,aa presented, have not been revmwed by Ihe Society of Palroleum Engmaere.and are subject to correctionby the author(a).The ma!erial, as presented, does not necessarily raflectany positionof lhe Socialy of PatrolaumEngineers, Ita officers,or members. Papera presentedat SPE mealings are subjectto publicationre’dw~by EditorialCommiltaesof the -societyofPetroleumEngineerk.PermsaiontocoPyiarastnctadtoan abstractofnotmorethan200 worde.Ilh.mlra!ionamay notbe copied.The abslractalmuldcontainconepicuouaacknowledgmentof where and by whom the papar is presented. Write Librarian, SPE, P.0. Box 83S8SS, Rlchardaon, TX 75083-2SS5 U.S.A. Telax, 730S89 SPEDAL.

!BSTRAC~ (3) After the mstdelis calIhted by propertrans-

This paper addresses the importanceof timely dataIationof reservoirgeologicdata and historicproduction

collection for proper reservoir management usingperformance data, sensitivity

simulationas a tool. Data requirementsfor black-studiescan be initiatedto ’optimizerecoveryand economics, Moreover, operational con-

oil, compositionaland steam simulationhave beendocumented. The interplay between various geo-

sideration$, such as the timing for waterhandling facilities or gas

sciencesand the proper translationof data ensurecompression

the successof such an effort.requirements,can be forecast.

INTRODUCTIONTh$s paper addresses the type of data that isrequired for black-oil,compositionaland enhanced

Reservoirsimulationis being used increasinglyas aoil recovery (EOR) simulations.

reservoirmanagement tool, In real life a given IMPORTANCEOF GOOD RESERVOIRDATAreservoircan only be producedonce. A model with apropergeologicaldescriptionfollowedby a history There is a saying: “If you think knowledge ismatch validation can provide the opportunity tohypothesize production under different scenarios.

expensive,just imaginehow expensiveignorancecanbee”

Sensitivitystudies can lead to productio~of thereservoirin the most optimum way. Coats defines The temptation will always be to short-cut datasimulation as the use of calculationsto predict acquisitionto reduce costs. It must be rememberedreservoirperformance,forecastrecovery,or co;~e;l~ that certaintypes of data, such as core derivedeconom+cs of alternative recovery methods. information, initial fluiddescribessimulationas a basic extensionof we?l-

properties, fluid

known rzservoir engineeringtheor~es and concepts,contacts,and initialreservoirpressures,can onlybe obtainedat an early developmentstage, The data

such as Buckley Leverett,or material-balanceequa-tionsthat tveredevelopedprior to 1960. Simulation

obtained plays a vital role in evaluating the

is a powerfultool for the followingreasons:developmentoptionsof a given reservoir.

(1) It provides the ability to simultaneouslyAn equallyvitalcomponentof reservoirsimulationIs ‘

incorporate the effects of a number oftranslationof thisdata in the properform. Some ofthe examplesof this type of knowledgeare transla-

variables such as gravity, mobility, rockheterogeneity,relativepermeability,capillary

tion of two-phase (gas-oiland oil-water)relative

pressure,and fluid properties,permeabilitydata to simulatethree-phaseflow.condi-tions. An additional need is understandingthe

(2) The process itself forces an engineer todifferencebetweenflash(separator)anddifferentialliberation.(reservoir)and the properrepresentation

closely examine all pieces of a reservoirand of this data into the simulator. Translationofall geologicalinformation. Insightis gained”regardingregionalperformancevariationsthat

geological models into reservoir flow units orboundarieswith proper size andnumbgr of grid cells

can be incorporatedinto simulation, This inturn provides momentum for better reservoir

will have an impacton simulationgeneratedresults.Two of the most interesting paper$ on model

management. misapplicationhavebeenwrittenby Coats and Staggset al.

Referencr?sand illustrationsat end of paper.

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2 DEFININGDATA REQUIREMENTSFOR A SIMULATIONSTUDY SPE 22357

lYPFsCIFsMJ~ IN WiEUL 1NDUSTR% geologicand reservoirengineeringdata is shown asFigure 1 from Harris.

The reservoirs most f;quently simulated containblack-oil. d’The term Iack-ofl means that oil is Reservoirs can be broadly classif~ed as clastictreated as a single component with no interaction (sandstone)or carbonate. It is re’lativelysimpletowith the gas or water phase. These models are descr~be a sandstone reservotr since modern daycapable of simulatingperformanceunder depletion, analogsprovideessentialmodels to do so. Figure2gas or water injection, water influx and oil from Harris and Hewitt7 presents the types ofdisplacement by movement of gas/oil or oil/water depositional sftes a sand reservoir can provide.contacts, They further classify these reservoirs into three

types of geometries. Figure 3 descr~bes theseCompositionalmodels accountfor interactionbetween layoutsgraphically.various hydrocarbonphases. Such is the case for arich gas condensateor a volatileoil reservotr, EOR Carbonate res~afi;~e8ar& g~erally difficult toprocessescan redescribed as: describe. in their paper

!’Distributionand Continuityof~arbonateReservoirs”o Miscible - CO and hydrocarbonInjectIon document such an effovt. Their experience is thate Chemical- po!ymerand surfactantinjection these rocks are heterogeneousboth in terms ofQ Thermal - steam,hot water and insitucombustion porosityand permeability. The depositionalprocess

itself is complex. Dlagenetic changes are veryMisciblesimulationsusuallyrequireuseofcomposi- random and can modify rock texture considerably.tionalsimulation,whereaschemicalprocessessuchas Generally dolomitizationhas a positive effect onpolymerand surfactantcan,besimulatedbya modified modificationof porosity. Figure4 from Jardine8etblack-oil simulator. Thermal simulatorsare quite al. shows how porosity in carbonatesis altered bycomplexsince in additionto fluidflow,they contain variousprocesses.heat flow equations. This paper will describe thedata requirementsfor steam injectiononly. During the exploration stage examination of core

cuttingsand analysisof core rock samplesare key toDATA RWEMENTS FOR~L CONSTRUCTION formulatinga depositionalmodel.

The information required to determine initial Reservoirdescriptionis a continuousprocess. i%distributionof rock propertiesand fluidquantities the field is developedthe models shouldbe reviewedis common to all typesof simulations.Types of data and modifiedas necessary. As reservoirperformancerequiredare describedunder followingcategories: data becomes available,the knowledgeof reservoir

discontinuitiessuch as faults,barriers,boundaries1) Reservoirdata -andstratificationbecomesmore refined.2) Fluid properties3) Field performancedata Another powerfultool that has become availablefor4) Enhancedoil recoveryconsiderations reservoirdescription.~s 3-D seismicdata. Recent

papers by Plet A RuijtenbergQet al. describe howRFSERVOIRDAT/) using 3-D seismic data results in a more complete

descriptionof reservoirboundariesand structure.lD.fW!RAUQ&&!dKM Figure 5 origin~~ly presented in thefr paper IS

shown. Robertson documentshow3-D seismiccan addThe amount of data availableto describea reservoir reserves and facilitate cost-effective reservoiris dependenton the developmentstage of the reser- management, The number and locationof developmentvoir. At an early stageof reservoirdevelopmentthe wells can be optimizedfor maximumrecovery,informationis availablefrom only a few wells. Thefollowinginformationsourcesare utilized: In many cases”older,two-dimensionalseismicdata can

be reprocessedto obtain more detailed information.1) Seismicdata Three-dimensionalseismicdata is also being used in2) Core analysis monitoring saturation fronts and locating oil3) Well logs previouslybypassed.4) Well test data

Tables 1 through4 illustratethe typeof informationthat can be obtainedfrom these sources. Matrix ReauirementS

The core analyses,well log and well test data are The integrationof depositionalmodel constructionacquiredfor individualwells, An integrationof all along with informationlisted in Tables 1 through4the informationhas t~ b~ made in order to describe shouldprovidethe necessaryinformationto describedistribution of properties in areal and vertical the variationin reservoirrock propertiesalongwithdimensions. This task ts called reservoir discontinuitiesand stratification. This variationdescription. is preparedas contourmaps. Table5 providesa list

of maps that can be prepared to describe them voir Descrfotiom reservoir.

The task is best accomplishedbyan interdisciplinary Alternate methods are available to describe waterteam consistingof geologists,geophysicists,well saturationand permeabilitydistribution.Thesewilllog analysts,productionand reservoirengineers, An be describedlater on. Other reservoirrelateddataexample of how this interplay can occur between items are:

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SPE 2235? A. K. DANOONA,R. B. AISTON, R. S. JOWNSON,R. W. BRAUN 3

&

.=+——

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1) Relativepermeabi1ity relativepermeabilitiesare a i%nctionaf their2) Capillary pressure for oil-water and gas-oil respectivesaturations. If three-phaserela-

system tiveperineabilitiesaregeneratedfrommeasured3) Rock compressibility gas-oil and oil-water data, it is best to4) Verticalpermeability5) Absolutepermeabilitydistribution

ensure measurements are made with proper

6 Initialwater saturationdistributionconsiderationofwettability.

17 Pay thicknesscut-offs @ Ensure that relativepermeabilitieshonor thedirection of change of wetting,phasesatura-

ative Permeability tion. Drainagerefersto a decreasingwetting-

Two-phaserelativepermeabilitysuch as that of oiltiphase saturationwhile imbibitionrefersto anincreasingwettingphasesaturation. Injection

gas or oil-watercan remeasured in the laboratory.Both steady-state and unsteady-statemethods are

of dry gas into an ail reservoiris an exampleof drainage,while injectionof water into an

available. Hassler, Hafford, and dispersed feed oil reservoiris imbibition.methodsmeasurerelativepermeabilitiesundersteady-.stateflow. Unsteady-staterelative permeability @ The dependenceof waterfloodresidual oil onmethods take less time. The BuckleyLeveretttheory trapped gas saturation can be handled.by ,?as extendedby Welge can be used to computerelative method suggested by Dandona and Morse.permeabilityratio from the followingrelationship: Stone’stkprobabilitymethod also accountsfor

such effects.f.=~=

1+ ~; ~ ~. (1) Properanalysisof 3-phaserelativepermeabilitydatak. PV is quitecritical. The engineershouldtake the time

to ensure that the end points of relative pwmea-bility data as well as the rest of the saturationrangeare properlyhandledwith regardto rocl(wetta-

JBT method,capillarypressureand centrifugemethods bility and gas entrapment.are used t;t~;;erm;;;ho~;ativep&~-~j~ilityusingunsteady relativepermeabilitycan sometimes”beestimated from field

CaDil18rvPress~

data, as follows: Capillary pressure is the difference in pressure

& acrossthe interfacebetweenwettingand non-wetting

k.= (Rp .R*)W2? fluids. For a gas-oil-water study, capillary

Do P. pressurecurveswill be requiredfor gas-oilandoil-(2) water systems. The data can be acquired in the

so= (1 - +?) (~) (1 “Sw) laboratory by measurements on core plugs. TheBoi mercury injectionmethod is rapid but destroys the

core. Other laboratory methods are displacementthrougha porous diaphragmand centrifugalmethods.

In the absenceof measureddata, two-phaserelative Another good source of such informationis well logpermeabilitiescan be approximate~zfrom published data where swell has penetratedthroughgas-oilandcorrelationssuch as those of Corey , oil-water contacts. Water saturationvs. distance

from gas-oil or oil-water contact can be plotted.The methodology to estimate two-phase relative The distance from the oil-water contact is.thenpermeabilityiswell established. Measurf$data for translatableto capillarypressure,three-phase relative permeability seldomavailable. Typically simulatorsare programmedto Rock Com~ressibilitycompute 3-phase relative permeabilityfrom 2-phasegas-oil and oil-waterrelativepermeabilities. The For normally pressured sands, rock compressibilityend points for each of the~~,tfurvesare honored in can be either measured in the laboratoryor derivel$the calculations. Stone’s p~obabilisticmodel from publishedcorrelationssuch as that of Hall.described as a set of equations is commonly used. However, for abnormal pressure sands such as thoseThe followingprecautionsshould be consideredwhen present in U.S. Gulf Coast, good correlationsareprocessingthree-phaserelativepermeabilitydata. unavailableand it is best to carry out laboratory

measurements.@ Examine the end oil saturationto the type of

displacementsimulated. Themathematicalmodel VerticalPermeabiltyiwill not permitoil saturationtogo below thatnumber. Many times relative permeabilityto Verticalpermeabilitycan play a significantrole inoil at low oil saturation is critical in some flow situations, such as coning, gravitypredictingreservoirbehaviortowardsthe later override, and cross-flow between sand layers.part of the reservoirlife. Geologicaldiscontinuitiesor thin, tight beds such

as shalesthat separatevarioushydrocarbonzonesaree Much of the published literaty~eis based on also important to vertical flow. Experience

water-wetrock systems. Stone describeswhy indicates thatbe;~e~nare significant p~n~rmancehis method is applicableto both water-wetand differences non-permeable 1Owoil-wet systems. In a water-wetsystem,water permeabilitybarriers. Avalue of zero for verticaland gas relative permeabilityis a dependent permeabilitycan isolate a horizontal layer fromfunction of water and gas saturation only. communication.(l ntheotherhand,a low permeabilitySimilarly, in an”oil-wet system, oil and gas (e.g., one red.)can permit significantcross-flow

2!57

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4 DEFININGDATA REQUIREMENTSFOR A SIMULATIONSTUDY SPE 22357

because of the 1arge cross-sectional areaperpendicularto horizontalflow.

Pav ?hi.cltwssCULQ!Y.

Verticalpermeabilityvaluescan remeasured on coreTo determinethe amount.of oil availablefor deple-tion, net thickness has to be determined. It iS

plugs and adjusted downward to account for shalelenses. Well test data such as interferenceand

quite easy to rationalize that non-porous, non-permeablerock volume such as shale mfxed with sand

pulse tests can also be used to estimate these should not be part of the pay. However,many timesvalues. a geologist,alsoappliescriteriawhich are based on

fl~solutePmmeabilitv Distributionporosity-permeabilitycutoffs as well as on water

—- saturationcutoffs. The rationalebehind this type

Conventional core analysis typically measuresof criteria is that rock below certain porosityorpermeability values will not contribute to the

porosityand absoluteairpermeabflity. Permeability reserves. However, it stands to reason that unlessis one of the most difficultparameterstopredfct In this rock volume is in non-connectedporosity,giventermsof variationand distribution. Well flow test enough time it should produce. In additionit alsoanalysisfrom build-upand fall off testscan provide provides additionalpressure support to the reser-permeab$lity x thickness (kOh) for the interval voir. Gas as a fluid can produce through muchtested. The advantage of this method is that it tighter rock as comparedto oil. During the dep7e-measures permeabilitlesand total flow capacity of tion phase almostall of the res+?rvoirin continuousthe system in-situ. It must reemphasized that kh bythis method is fn effect kh or k$h as the case may

pore space should contributetu the recovery, Ho,w-

be. A transformof severs!values of koh from testever, dur!ng waterfloodor other recoveryprocesses,

data should be comparedwith core analystscomputedpart of the rock volume in the tight pore spacemay

kh. Asignificantlyhigh ratioof’kh/kCO,,hindicatesnot contributet.orecovery, In otherwords,cut-offsare processdependent.

presenceofvugs and fractu+esin ?he system.Enhanced oil recovery processes requfre additional

Sincethe numberof coredwells is typicallylimited, data. Table 6 provides a l~st of the specialthe areal distribution must be estimated from reservoir data needed for miscible, chemical andporosity-permeabilitytransforms. Core porosity steam simulation.sample data is plotted on a linear scale vs.permeability data on a log scale. Regression ~LUID PROp~RT1~analysis is performed to fit a curve through suchdata. Since porosity for most wells is also We have provided guidelines for translation ofavailablefrom well logs, this transformcan then beused to calculatepermeabilitydistribution.

geological and rock data for a simulation study.Fluidpropertydata acquisitionand analyslsare alsovital componentsof a’data collectionprogram. One

Figure17 6 shows such a transform. It is ourexperiencethat scatterof data is considerableand

of thelgmostcomplete papers on this subject is byMoses. He stressesthe importanceof accuratefluid

as such it is difficult to predict values of samples: “Fluid samplesmust be taken early in thepermeability, At times some consideration of life of the reservoirto obtain samplestruly repre-depositionalmodel, rock types and facies reduces sentative of the reservoir fluid. ‘They should bedegree of scatter. it is recommended that a taken only after a carefully planned well condi-transformbe developed for each major rock unit or tioning and testtng program. When the PVT datafaciesto reduce scatter, obtainedfrom these samplesare used, care shouldbe’

taken to adjust FVF’s and gas-oil ratios (GOR’S)for~nital Wateri SaturationOistributioq surfaceseparatorcondition.”

Inittal water saturation by layer can either be The properunderstandingof the fluidbehaviorsystemmappedby averagingwater saturationvaluesover eachinterval (Table 5) or computed using the ‘J’

as a function of pressure and temperature isessential. Figure 7 is a pressure.temperature

-function.Actual saturat~onvaluesare computedFrom diagram illustratingthat’the initial fluid systemthe electriclogs based on resistivityvalues. The“J” function approach is essentiallya correlation

can be broadlycategorizedas:

that fits initial water saturation values t18 black-oilsor low shrinkageoils,permeabilityand porosityvalues, Rose and Bruce :]describe the method in detail and express the “J”

volatileoils or high shrinkageoils,3)

functionas follows:gas-condensatesystems,and

4) gas systems,both wet and dry gas.

J(SW) = ~ :;~e[

It is noted that a given fluid system goes through&

(3)Ow c

several changes as pressure on the system changesduring the deplettonphase of reservofr.

The reservoirfluid samplefor study is obtainedfromPorosity and permeabilitydistributionis obtained bottomholesamplingor from recombinationof surfacefrom the map of each layer. UOW is the interracialtension between oil and water and d is the contact

separator samples of gas and liquid. Analyses ofthese separator samples are performed in the

anglebetweenthe interfaceseparatingthe two fluids laboratoryand the fluidsare then recombinedto theand the surface of rock. The advantage of this desired reservoirfluid composition,producinggas-method is the ability to compute water saturation oil ratio (R., SCF/ST13). From this point both thedistributionfor each model cell or node based on bottomholesample and recombinedsa~le are examinedporosityand permeability. utilizingthe identicalprocedure. The following

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SPE 22357 A. K, lMNKJONA,R. B. ALSTO1

informationwill be obtainablezlfromthe series oftests on the black-oilsamples.

1) Compositionalanalysis

2) ~;nstantmass studysaturation ressure

b) !pressure-voume relationsc) oil compressibilityat variouspressuresd1

fluid relativevolume factorse volume percent liquid as a function of-

the pressure

3) I);fferentialvaporizationstudysolutiongas as a functionof pressure

b) formationvolume factoras a functionofpressureliquiddensityas a functionof pressure

:] gas gravity as a functionof pressure

4] Equilibrium liquiddetermination

phase viscosity

5) !$paratorflash optimizationstudyproducinggas-oilratioas a functionofseparatorpressureat room temperature

b) oil formationvolumefactorbasedon roomtemperatureflashedoil

c) producedgas composition

Table 6 is the list of fluid data for a black-oilsimulation. As the reservoir fluid propertiesapproachthose of a high shrinkageoil/volatileoilsystem,it becomesmore advantageousto obtain addi-tionallaboratoryinformationin orderto predictthefluid behavior during normal reservoirdepletion/-production. In addition ~~=t~~ analysesperformedfor the black-oil system, ‘ ‘ the followingtestshould be performedfor the volatileoil samples.

1) Constantvolume depletionstudya) equilibriumvapor-phasecompositionb) fractionof well streamproduced

equilibriumgas deviationfactors:1 liquid-volumeshrinkagebelow saturation

pressureto abandonmentpressure.

The gas-condensatesystem25requiresdata that is verysimilar to that of the volatileoil system. Unlikethe black-oil.or volatile oil systems, bottomholesamples should not be u$%d for obtathing gas-condensate.fluid samples. Also because thisreservoirfluid is gaseous at reservoirconditions,no liquid-phase viscosity or separator flashoptimizationtests are performed. After successfulseparator fluid analyses, the followingtests areperformed:

1) Modifiedconstantmass study (visualcel1 only)for a seriesof recombinedgas-oilratiosa) pressure-volumerelationsb) dew point pressures

liquidvolumesas a functionof pressure~~ mixture densities

gas phase compressibilityfactors .f) gas formationvolume factors

2) ~;nstantvolumedepletionstudyhydrocarboncomposit~onof the liberatedgas

b) retrogradeliquid-volumemeasurements

R, S. JO!lMON,R, W. BRAON 5

The final type of reservoir system is the wet-gas/dry-gas. As indicatedby the~rdesignation,bothof these fluids exist in the gaseous state underreservoirconditions. PVT data would give only thefluid density and gas compressibilityfactor (Z).The only differencewould occur at the surfacewherethe wet-gas system would produce some very lightliquid, usually less than 10 STB/flMSCFof producedgas.

The increasedinterestin EnhancedOi1 Recovery{EOR)confrontsthe simulationistwith new problemsin hisattempts to successfullypredict actual reservoirperformance. Most CO or hydrocarbon misciblefloodingoperationswou?~requirethe followingteststo be performed.

1) Slimtubedisplacem~h~studiesa) determine minimum miscibility

pressureat the reservoirtemperatureb) estimate the average residual oil

saturationafter COZ flooding,

2) Singlecontactmiscibilitystudies--pressure-volume relationsfor a seriesof C02-reservoirfluid mixturesa) bubble point or dew point pressureb) single phase foriyationvolume factor

(swel1ing factor)single phase fluiddensity

:; liquidvolumesas a functionof pressure

3) Liquid phase viscosity determination --preferablyon two COz/reservoirfluidmixturesfrom the bubblepointregion

4) Vaporizationstudiesa) determine the optimum vaporization

pressure (OVP) at the reservoirtemperature

b) determine the maximum recovery fromvaporizationonly

c) determine hydrocarbon distributionthroughC + on

%stoc tank oil;: producedliquidcondensate3. residualliquid4. produced vapor (includingliquid

contentas STB/MMSCF)

The aforementionedwish list basically summarizesdata required for various types of fluid systems.Proper interpretationof this data fo;o~e;l~mulationstudy requires additional skills. in hispaper describes differences between flash anddifferential liberation, It is comnonly believedthat a given reservoir resembles the differentialliberation process In the reservoir and a flashseparation occurs in the production lfnes andseparator. However, the reported production isalways stock tank bbls. Thus, it is essential tocombine both flash and differentialliberationsforFVF and GOR functionsfor proper re~resentationofdata in black-oilsimulation. Moses describestheprocedureto do that in his paper.

Compositional simulations for rich condensate orvolatileoil systemsrequirerepresentationof fluidbehavior using an equation# state such as Peng-Robinsonzbor Redlich-Kwong. In order to reducecomputationaltime,hydrocarboncomponentsare lumpedinto subgroupssuch as Cl through C3, C5 through Gb

259

-.,

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6 DEFINING DATA REQUIREMENTS Ff)R A STMTIT.ATTC!M STIMV Sm? 29?57..-. .-. .—-.—---- .-. . -- ------- ------ ----- --- ---~.

and CT+. For increaseddetail, the C,+ group is descrtpt~on. The early breakthroughof injectedfrequently broken into two or three subgroups. fluids may indicatehigh permeabilitystreaks. IfLaboratorymeasured data such as retrogradeliquid breakthrough timing does not match, ‘relativedrop-out (Figure 8) is matched using component permeabilityshouldalso be re-examined.grouping. The computationaltimes are three to fivetimesmore comparedtothe black-oilsystems. Models Continuousflowmeter logsor spinnersurveyscarriedare generallyunstablenear the criticallocusof theP-T diagram.

out on injection and production wells can helpdetermine the entry and exit point of fluids. Foropen hole completions,electriclogs can helpmonitor

Additionaldata requirementsfor EOR are given in gas/oil and water/oil contacts or changes in waterTables 7, 8, and 9. saturation. For cased hole completionsTDT logs can

be useful in providingdetailsof fluidmovement. Af3ELD pERFORMANCE0A7A model capableof duplicatingthe measuredfielddata

provides a high level of confidence in predictingfl~auistion and pei rformancePredictio~ future behavior of the reservoir. Various future

operatingstrategiessuch as recompletionprograms,The simulator calculates the fluids in-place and timing of gas lift installations,etc., can now betheir distributionafter geological,rock and fluid examined.data are properlyinput into the.model.

Simulation for a fully developed reservoir isFor the purpose of this discussionwe can consider basically an extension of the Intermediatesta e.the field to be in various stages of development. !However,by this time reservoirdescriptionhasfu lyThese can be: matured. Movements for various fronts such as gas

and water have also been matched. It is equally1. Earlydevelopment-- under productionfor less importantto determinewhere remainingoil is present

than a year. in the reservoirand what ts ultimatelyrecoverable.A point of caution here is to examine the relative

2.” intermediate-- producing under depletion or permeabilityto oil at low oil saturations.pressuremaintenancefor less than five years.

~NHANCEDOIL ~OVERY SPECIALCONSIDERTION~A3. Fullydevelopedreservoirunder productionfor

10+ years. Simulationpredictionsbecome more complex for EORmethods, In most cases historicalperformancedata

4. Field under EOR. is not available. Additionalwork has to be done toclosely.determine remainingoil saturationand its

The performancedata can be categorizedas: distributionin the reservoir.

(1) well completiondata Mi$ctbte (C~2’Hv~.

carb n)o Floodinq(2) production/injectiondata

Compositionalsimulation of enhanced oil recoveryWell data relates to tubing and casing size, processes such as C02 requires characteriza$..g~ofperforation intervals, timing of any workover or fluid behavior using an equation of state. ‘ Arecompletion,productivityor injectivityindex of step-wiseprocedureto simulationis as follows:each well.

1. Match laboratory work using an equation ofThe oil rate, GOR, WOR and pressurevs. time data on state program.a well-by-wellbasis are needed to conducta history 2, Use one-dimensional, sma19 grid cells tomatch. ct;gt];;telab test data such as slimtube

For a field in the early developmentstage, usually 3. tl;l~iz; slug size using a one-dimensionalit is possibleto derive the followingbenefitsfromsimulation: 4. Condu;t simulationon a pattern or smallest

;Tm;;ical element to optimize operating(1) close match of fluids in place from geological

analysisand model description. 5. Scale ;esults on field-wide basis based onpatternresults. Verify those resultsbyctin-

(2) establishmentof recoveryunder depletionand ducting limitedfield scalemodel simulation.range of recoveries for immiscible fluidinjection. The abilityto predictthe performanceof.areservoir

under enhancedoil recovery (EOR) is more difficult(3) optimumtimingatwhich injectionshouldbegin. than for black-oil. EOR models are highly process

dependent. In additionto having reservoirand EOS(4} rate-time forecast to help determine present” knowledge,one has to confronttranslationof multi-

economicsof the field. contactmiscibilitydata into the simulator. S1im-tube data is one-dimensionalwhile the reservoircan

At an intermediate stage of development the have 3-dimensionalflow. Part of the reservoircangeological,rock, and fluid descriptionas well as be “immiscible,part partially miscible and partinitial fluids in place can be verified more completelymiscible. The possible changes in rockaccurately. Geologicaldescriptionis a continuous nettabilityor interfatialtens~onand correspondingprocess. In this”stageif the geologicaland fluid changes in residualoil saturationare difficulttodescriptionsdo not providea match with performance preciselydefine and fine-tune.data, it is necessary to review and change the

280

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SPE 22357 At K. IMNOONA.R. B. ALSTON.R. S. JOHNSON,R. We BRAUN 7

-:—=5.—,

—

—

-.... .

Since a significantportionof EOR simulationstudyis for planningpurposes,the results are useful interms of relative comparison of cases. If theobjective Is to establish ultimate recovery, fieldperformancedata from similarreservoirsfloodedwithsimilar fluids should be reviewedas an analog. Iffield pilot test data is available,such data shouldbe carefullymatchedbefore scalingthe resultson afieldwidebasis.

cal (PolvmerlSurfactantl Floodinq

Polymers and surfactant chemicals are added toinjection water. Polymers are used to providemobility control during displacementby increasingwater viscosity and reducing rock permeability.Selective injection profile control in which highpermeabilityzones are blocked to alter injectionprofile is another application, A black- oil modelcan be modified to simulateperformance. Stabilityof polymer at reservoir.temperatureand its inter-action with formationwater should be evaluated inthe laboratory.

Surfactants decrease re;;~;;onoil saturation byreducing int.erfacial Considerablelaboratory work is required to”find an effectivesurfactant system and to perform core floods. Ablack-oilmodel capable of tracking injected fluidconcentrationand itseffecton relativepermeabilitycan provide incrementalforecastsof oil recovery.

As is the case with miscible floocisimulations,chemicalfloodingshouldfirst be simulatedon smallone-dimensional models to duplicate laboratoryresults. Pattern simulationscan then be followedwith reservoirscale studies.

Be rmal (Steam) Floodiqn

The advantagesof steam as a medium for moving heatto a displacementfrontare its relativelyhigh heat-carryingcapacityplus the largeamountof heat whichmay be transferred to a formatian as heat ofcondensation.

The simulationmodel shou9daccountfor heat loss insurfacefacilities,injectionwell bore a~~ verticalloss to the surroundingstrata. Figure , 9 is”anillustrationof heat losses which occur. Modelmathematics in addition to fluid flow and heattransfershouldalso accountfor:

1. Thermal expansion of oil -- this results inreduced SQP when reservoir temperatureapproachesInitialtemperature.

2. Viscosityreductionpermittingmore efficient‘immiscibledisplacement.

3. Steam distillationif reservoiroil containsdistillablelight components.

If field production data is available, a matchbetween measured and computed oil, water and steamrates is.obtained. It is importantto match steambreakthrough times as well as API gravity andviscosityof producedoil. Steamfloodsimulationiscomplex and does require significantly moreengineeringand computertime. It is more convenientto simulatea portion (or pattern)of the reserwoirand then scale the kesults.

1

WLISI of’i~

We have described the data requirements forconducting a simulation study for black-oil,compositionaland enhanced oil recovery processes.The followir,gconclusionsare made:

1. Data requirementsshguldreconsideredearlyinthe life of reservoir.

2. Interdisciplinaryteams shou~d be used forreservoirdescriptionand data analysis.

3* Sensitivityruns should be made to determinewhich data parameters i~avekey influenceonresults. Everyeffortshouldbemade to obtainthat data.

4. If model-computedperformancedoes not matchfield data, do not force fit the historymatchbut review each data parameterand its impacton results.

5. Compositional and EOR simulation should befirst conducted with one-dimensional andpatternmodels. Pattern simulationscan thenbe followedwith field scale studies.

ACl(NflWLEllGEMIViT$

The authors wish”to thank the managementof TexacoEPTD for providingencouragementand fundingfor thesupportof this effort..

BFFERENQS

1.

2.

3.

4.

5.

6.

Coats,K. H.: “Reservoirsemulation: Stateofthe Art”, J. Pet. Tech. {Aug. 1982) 1633-1642.

Odeh, A. S’.: “ReservoirSimulation-- What isit?”,J. Pet, Tech. (Nov. 1969) 1383-1388.

Coats, K. ii.: “Use and Misuse of ReservoirSimulationModels”,J. Pet. Tech. (Nov. 1969)1391-1398.

Staggs, H. hi.and Herbeck, E. F,: “ReservoirSimulationModels--AnEngineeringOverview”,J.Pet. Tech. (Dec. 1971) 1428-1436.

Keelan, C).: “Coring”,world Oi1 (March 1985)83-90.

Harris, 0. G.: “The Role of Geoloav inReservoir SimulationStudies”,J. Pet.‘~ech.(May 197S)625-632.

7.

a.

9.

Harris,il.G. and Hewitt,C. H.: “SynergisminReservoir Management GeologicPerspective”,J. Pet. Tec~~ (J~!’~1977) 761-770.

Jardine, 0., Andrews, D, P., Wishart, J. W.,and Young,J. ii.:“Distributionand Continuit.vof CarbonateReservoirs”,J. Pet. Tech. (Jul~1977) 873-885.

Ruijtenberg,P. A., Buchanan, R., and Marke,. “Three-DimensionalIlataImproveReservo\r

!;~ptngw,J. Pet. Tech. (Jan. 1990)22-25,59-61.

2$1

. *

R lll?k’TNTNC IMT’A REOIITllFMF.NTE FOR A SIUULAT’ION STUDY SPE 22357

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

2’2,

23.

24.

25.

26.

--- ~..-.,- -“.-....-=---.—------.....-

Robertson,J. D.: “ReservoirManagement Using30 Seismic Data”, J. Pet. Tech. (July 1989)663-667,

Honarpour,M,, Koedertiz,i-.anc!fHarvey,fi.H.:“Relative Permeability PetroleumReservoirs”, CRC Press Inc., Boca Raton,Florida (1986)1-13.

Corey, A, T.: “The InterrelationBetweenGasand Oil Relative Permeabilities”,Prod. Mun.19, 38, 1954.

Stone, H. L.: “Estimation of Three-PhaseRelativePermeability”,J. Pet. Tech, 2, 214,1970.

Stone, H. L.: “Estimation of Three-PhaseRelative Permeabilityand ResidualOil Data”,J. of Can. Pet. Tech. 12, 53, 1973.

Dandona,A. K. and Morse,R. A.: “HowFloodingRate and Gas Saturation Affect waterfloodPerformance”,Oil and Gas Journal,July 2 and9, 1973,

Hall, A. C.: “Effective FormationCompressibility”,Trans.AIME (1953)198, 309.

Levorsen,A. 1.: “GeologyofPetroleum, SecondEdition”, W, H. Freeman PublishingCo., SanFrancisco,(1967) 128-129.

Rose, W. and Bruce, W. A.: “EvaluationofCapillary Character in Petroleum ReservoirRock”,Trans. AIME (1949)186, 127-142.

Moses, P. L.: “EngineeringApplicationsofPhase Behavior of Crude Oil and CondensateSystems”,J, Pet. Tech. (July 1986) 715-723,

Reservoir Fluids Laboratory, Inc.: “ProduceDescriptionand PriceSchedule,NorthAmerica”,Houston,TX, Jan, 1991.

Whitson, C. H. and Torp, S. 6,: “EvaluatingConstant-VolumeDepletion Data”, J. of Pet,Tech. (March 1983)610-620.

Jacoby,R. H. and Berry,W. J., Jr,: “AMethodfor Predicting Oepletion Performance of aReservoirProducingVolatileCrudeOil”,Trans.AIME, 210, 27-33, 1957,

Cook, A. B., Spencer,G. B. and Bobrowski,F.P. “Special Considerations in PredictingR~;ervoirPe ‘orrnanceof Highly VolatileTypeOil Reservoirs’,Trans.AIh?E,192,37-46, 1951.

Reudelhuber, F. O. and Hinds, R. F.: “ACompositional Material Balance Method forPrediction of Recovery from Volatile OilDepletionOrive Reservoirs”,Trans.AIME, 210,19-26, 1957 (?).

Coats, K, H.: “Simulationof Gas-CondensateReservoirPerformance”,SPEJ (Oct.1985) 1870-1886.

Peng, D. Y. and Robinson,’D. 0.: “A New ?wo-Constant Equation of State”, Ind. Eng. Chem.Fund (1976) 15, 59-64.

Redlich, O. and Kwong, J. N. S.: “On theThermodynamicsof SolutlonsV, An EquationofState Fugacitiesof Gaseous Solutions”,Chem.Reviews (Feb. 1949) 44, 233-244.

Ramey, H. J., Jr.: “Fundamentalsof ThermalOil Recovery’l,p. 165, Dallas, The PetroleumPublisi~ingCo., 1965,

262

.Informationfrom SeismicRata

—.— ~G#dw

1. Structure- size, shape,orientationand continuity

2, Gross thicknessof reservoir

3, Presenceof faultsor discontinuitiessuch as unconformitytruncation

4, Fractureintensityand orientation

5, Type of fluid -- gas or liquid

6. Cross-welltomography,techniquescan providedistributionof bypassedoil-- useful for EOR

—

InformationFrom Core Analysis5

GEOLOGICAL

L3,

4.

t

;:9.10.

11,

Formationlithology(sandstone,limestone,dolomite,etc.)Sedimentary structures (laminations,cross-bedding,root casts, wormburrows)Porositytype (storagecapacity)

intergranular vugular-moldicintragranular fractureintercrystalline micraporosity

Permeability(flow caoacitv)Presenceor absenceof oil (fluorescence)Formationpresenceand thickness(topsand bottoms)FormationsequenceFormationage, facies and correlation(biostratigraphy)OppositionalenvironmentFracturedefinition

depth and Occurrencelengthdepth anglewidth

Oiagenesis(chemical,physicaland biologicchangesafter deposition)

ENGINEERING

Porosity;: Permeability3. Permeabilityheterogeneity(Lorenzecoefficient,variancefactor)4. Porosityvs. permeabilityrelationships

Reservoirwater saturations(oil-basecores);: Reservoirresidualoil saturationsand distribution(pressureand sponge

core)7. Data for calibrationand refinementof downholelog calculations

Grain densityCalcimetry(limestone/dolomiteratio)AcousticvelocityGamma-raycharacteristics(coregamma and core spectral)Electricalproperties(“m” and “n”)Mineralogyand clay type, distributionand quantity

8. Specialcore analysisRelativepermeabilityFormationnettabilityCapillarypressure(water-retentionproperties)Pore volume compressibilityRock-injectedfluid compatibilityResidualgas (trappedby water)

... .... ..—.... IwnEQ

InformationFrom Well Leas

1.

2.

3.

4+

5.

6.

7,

8.

9.

1.

2.

3.

4.

5.

6.

7.

8.

3.

4.

5.—

6.-.

7.

Structuraltops

Gross/netpay thickness

Porosityvs. depth

Initialwater saturationvs. depth

Presenceor absenceof shales

Depth of gas/oil or oil/watercontacts

Well to well correlationsa continuityof sande verticalstratificationdefinition

Gas-oil and oil-watercapillarypressuredrainagecurves

Lithologydefinition

IAQIJu

Mel! Test Data

Reservoirpressure

Effectivepermeabilitythicknessproduct (kOh,k~h)

Productivity,injectivityindex,completionefficiency(wellboredamage)

Distanceof well from the fault or discontinuity

The size of reservoir(continuityof sand)

Single or double porositysystems

Continuityof permeabilitybetweenthe wells -- interferencetesting

Presencecf fracturesor high permeabilitystreaks

IMLL5 EReservoirInformationRequiredfor a SimulationStudy

Structuremap of each reservoir

Isopach maps (net and gross thickness)with location of gas/oil andoilwatercontactsfor each layer

1/0 porositydistributionfor each layer

Rock region maps for each layer

Maps of flow barrierssuch as faults for each layer

Water saturationmaps for each layer

Permeabilitydistributio~maps for each layer

Note: Layer is a continuous ‘lowunit. It may or may not communicatewithlayers above and below, Their primaryfunctionis to define stratificationinthe reservoir.

.

TA!3LE6

FluidData for Black-OilFrom LaboratoryMeasurements

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

Oil FVF vs. reservoirpressure

Gas FVF vs. reservoirpressure

Water FVF vs. reservoirpressure

Oil viscosityvs. pressure

Gas viscosityvs. pressure

Gas in solutionvs. reservoirpressure

Water viscosity

Oil compressibility

Water compressibility

Oil FVF at separatorconditions

Gas in solutionat separatorconditions

IM4L..z

AdditionalReservoirRock Data for EnhancedOil Recovery*

Miscible [CQ2avdrocarbon\

o Changes in rock nettability

● Effect on relativepermeabi1ity (S.,)

Chemical (D olvmer. surfactant~

@ Polymer/surfactantabsorptionon the reservoirrock

@ Polymer residual resistancefactor (~ffectof adsorptionon rockpermeability)

@ Polymer inaccessiblepore volume

a Rock ion exchangecapacitywith injectedfluid

@ Effect on relativepermeability’(SO,)for surfactant

Thermal (steam~

@ Temperaturedependentrelativepermeabilitycurves

@ Residualoil saturationto steam vapor {S.,9)

e Pore volume compressibility

● Rock thermalconductivity

c Rock heat capacity

●

In some cases these data cannot be measured directly and must bedeterminedby historymatchinglaboratorycore flood recoveries.

265

.—..—.

AdditionalFluid PropertyDatafor ChemicalFlooding(Polymer/Surfactants)

.?QIMU$

1. Stabilityof polymerat reservoirtemperature

2. Polymerviscosityvs. concentrationand shear rate

3. Core flood recoveries

Surfactant

1. Solutionstability

2. Phase equilibrium(oil-waterdistributionof surfactant)

3. Change in interracialtension I

AdditionalFluid PropertyDatafor ThermalFlooding

1, Temperatureand pressuredependentequilibriumconstant (k-values)

2. Viscosityas a functionof temperature

3. Thermalexpansionand heat capacityof oil

TYPE w EXAIVIPL.ES(X=6iE0i&3iNC ACWITY INTERPLAYC)FEWORT

ROCK!5TUDIES● LITHOLOGY

● DEPOSITIONALORIGIN

● RESERVOIR ROCKTYPES

r 1 .1

COREANALYSIS

es. m.t’-,,,fimw-c.w, ,m, Pn—

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I . CNJALITYPROFILES ~

I . RESERVOIRZONATION k

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. PORE VOLUME

. TRANSMHJfj!LIW1’

Fig 1 Inlograllonofgeoloy(~&reservoireflg[o~et!flgdata&

266

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Fig 2 Depostmnnlstos of siredand namirsof seinl.bodytypes ~

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Fig.3 Principoltypesat sandstoneresetvoirQeomelries~

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DEPOSITIONALCONFIGURATION I QRAIN I Pcwoslw

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SIZE TYPE EFFECTS EFFECTSI

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Fig.4 Poroslfy01carbonts:asII

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— LAB MEASURED DATA

~ A\ A EOS CHARACTERIZATION -BASED ON 3 PSEUDO

‘A

\

COMPONENTS (Cd . (23C4 - (27

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PRESSURE (PSIA)Fig.8 Retrograde ccndenset!on during depletion

HEAT LOSS FROM SURFACE EQUIPMENT TO SURROUNDING

I .-wI\}lllllltll{f//(j/ l)/s L

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‘1 I I : WERTICA~ HEAT ‘0SS FROM HEATED FORMATION-.-111- $

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FIg 9 Illustrationof heat Ioaseswhichoccurin a heat InjectionGyslem(afterRamay m)

270