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SPE-38473-MS

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SPE 38473 MS
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SocietyofPetroleumEngineersSPE38473Using3DGeologicalModellingandConnectivityAnalysistoLocateRemainingOilTargetsintheBrentReservoiroftheMatureBrentFieldFVAbbots,BrentFieldUnit,ShellUKExplorationandProduction;A.D.vanKuijk,ShellInternationalExplorationandProductionBV,ResearchandTechnicalServices(RTS),theNetherlands;Copyright1997.SocietyofPetroleumEngineers.Inc.Thispaperwaspreparedforpresentationatthe1997OffshoreEuropeConferenceheldinAberdeen.Scotland.9-12September1997.ThispaperwasselectedforpresentationbyanSPEProgramCommitteefollowingreviewofinformationcontainedinanabstractsubmittedbytheauthor(s).Contentsoftilepaper,aspresented,havenotbeenreviewedbytheSocietyofPetroleumEngineersandaresubjecttocorrectionbytheauthor(s).Thematerial,aspresented,doesnotnecessarilyreflectanypositionoftheSocietyofPetroleumEngineers,itsofficers,ormembers.PaperspresentedatSPEmeetingsaresubjecttopublicationreviewbyEditorialCommitteesoftheSocietyofPetroleumEngineersElectronicreproduction,distribution,orstorageofanypartofthispaperforcommercialpurposeswithoutthewrittenconsentoftheSOCietyofPetroleumEngineersisprohibited.Permissiontoreproduceinprintisrestrictedtoanabstractofnotmorethan300words;illustrahonsmaynotbecopied.Theabstractmustcontainconspicuousacknowledgmentofwhereandbywhomthepaperwaspresented.Writelibrarian,SPE,P.O.Box833836,Rid1ardson,TX75083·3836,USA,fax01·972-952-9435.AbstractAspartofthedrivetolocateremainingoiltargetsintheBrentFieldpriortodepressurisationI,full-field3DstaticreservoirmodelsforthemainBrentField(excludingthefaultscarpdegradationareacalledthe'slumps,2)wereconstructedlastyear.BoththeBrentGroupandtheStattjordFormationreservoirsweremodelledusingtheShellproprietry3DgeologicalreservoirandpropertymodellingprogramknownasGEOCAp3,4.ThispaperbrieflyoutlinestheapproachtakenintheGEOCAPmodellingoftheJurassicBrentGroupNessreservoir,whichformedthebasisforthefirsttest-caseapplicationofanewwell-clusteringtechnique,CRF(CumulativeResistancetoFlow)whichisthefocusofthispaper.TheCRFmoduleisoneofthelatesttechnologicalenhancementsofGEOCAP,developedbyius(ShellInternationalResearchandTechnicalServices,Netherlands).Itisapermeability-distancebasedwell-clusteringmodule,thatcalculatesconnectedreservoirvolumetoperforations,usingtheGEOCAP3Dpermeabilitymodels.Subsequentremovaloftheseconnectedrock-volumeclustersfromthemodel,resultsina3Dmodelofunconnectedreservoirvolume.Themodelcanthenbeusedtoidentifyunconnectedareasthatarelargeenoughtobeconsideredaspotentialremainingoiltargets.Theseareasthenwarrantfurtherinvestigationaspotentialtargetlocations,mostimportantlyintermsofdynamicreservoirmodellingaspects,andcalibrationwithlatestsurveillancedata.TheresultsindicatethattherearestillseveralsizeableColorPrintingpaidforbyShellU.K.ExplorationandProduction107'targets'(inexcessof1MMbblsSTOlP)leftintheNessreservoirafterthecurrentlyplannedwellshavebeendrilledandthesearecurrentlyundergoingindependentreview.IntroductionTheBrentFieldiscurrentlypenetratedbyover200wells,hasbeeninproductionfor20yearsandhasproducedmorethan1750MMbbisofoil.Asaresultofthe1995-96LTRO(LocateTheRemainingOil)campaignS,20wellswereplannedtoaccessanestimated50MMbbls+recoverableoil.Atthetimeofwritingmostofthesewellshavenowbeendrilled.Studiescoveringallpetroleumengineeringaspectscontinuetotrytolocateanddevelopfurtherremainingundrainedoilpriortotheyear2004,whendecliningpressureswillcausewellstoloselift,limitingoilproduction6.TheobjectiveoftheGEOCAPmodellingprojectfortheBrentFieldreservoirswastousethepowerfulfunctionalityavailablewithinthesystem(particularlythedetailedfaciesmodellingcapabilities)totrytolocateremainingunsweptsandsinthefield.GEOCAPfunctionalityenablestheintegration,synthesisanduseofvastamountsofdatainthegeologicalandpropertymodellingprocess:welldata,petrophysicallogs,corefaciesdescriptions,core-plugdata,perforations,seismicsurfaces,faults(sealing/non-sealing),fluidcontacts,rockpropertydataetc.Thisdataisthenusedtoperformreservoirunitcorrelations,faciesidentificationfromlogs,intra-reservoirunitdetailedfaciescorrelationsandthesubsequent3Dmodellingofgeneticfaciesbodies.The3Dgeologicalmodelisconstrainedbyseismicsurfaces.Thefundamentalprincipleofthe3Dpropertymodelling(porosity,permeabilityandsaturation)isthatitiscontrolledbythe3Ddetailedfaciesmodel.GEOCAPalsocontainsfunctionalityforwell-planningandwellevaluation.OutlineoftheGEOCAPmodellingprocessOver130wellsthatpenetratethemainBrentreservoirwereusedtoconstructthe3Dgeologicalmodel(Fig.I).Correlationofthe17reservoirzoneswasperformedanddetailedwelltowellfaciescorrelationswerethencarriedoutattheintra-2F.V.ABBOTS.A.VANKUIJKSPE38473reservoirzonelevel,tofomlthebasisofthe3Dfaciesmodel(Fig.2).Thismodelincorporatessomenewfaciesinterpretationsresultingfromthe1996sedimentologyandichnofaciesreviewofallNessreservoircorematerialfromtheBrentField.Thedeltaicfluvial-shallowmarinefaciestypesmodelledintheNessFormationhaveadifferentsedimentologicalgenesis,arecharacterisedbydifferent3Dgeometriesandshowdistinctporosity-permeabilityrelationshipsandtrends.A3Dporositymodel(Fig.3)wasobtainedbyusingthe3Dfaciesmodelandthecalculatedpetrophysicalporositycurveforeachwellinthepropertyinterpolationmodule,whichhonourswelldataandthenusesittointerpolatewithintheconstraintsofthe3Dfaciesmodel,therebymodellingverticalandlateralporositytrends.Thehorizontalpermeability(kh)modelwasconstructedbyusingthe3Dfaciesmodelandthe3Dporositymodeltogethertoassignapermeabilitybasedonfacies-dependent,logporosity/coreplugkhrelationships.Similarlytheverticalpermeability(kJmodelwasobtainedbyapplyingfaciesdependentcore-plugderivedkh-kvrelationships.These3DpermeabilitymodelsforkhandkvformtheinputtotheCRFanalysis.ThephilosophybehindCRFclusteringTheCRFmodulewasdevelopedin1996andisanintegralpartofGEOCAP'sclusteringanalysismodule.Thisstudywasthefirsttest-caseapplicationofthisnewtechnicalenhancementofGEOCAP.CRFclusteringdefines3Dconnectivitytowellperforationsasafunctionofbothdistanceandpermeability,whichisamajoradvanceoverpreviousclusteringfunctionalitywhichwasbasedsolelyonfixeddrainageradiiaroundthewellbore.ThetechniqueisbasedonasimplificationofDarcy'sLaw,describingtheresistancetoflowthatisencounteredasaresultofincreasingdistanceandpermeabilitychangesawayfromtheperforatedintervals.Ifthevariableseffectedbytime/temperature/pressure/gravityloil-composition/production-rate,suchasviscosity(11),flowrateandpressure(P)arenegatedfromtheDarcyequation(theseparameterscannotbehandledinastaticreservoirmodellingenvironment)theequationcanbesimplyrearrangedtogivecumulativeresistancetoflow(CRF)asafunctionofdistanceandpermeability:Flow=kill*aP/axrearrangedtoCRF=faxIk[m/mD](integraltakenalongpathofleastresistance)CRFtakesintoaccountthatconnectivitywillextendfurtherawayfromtheperforationsinhigherpermeabilitysands(suchaschannels)thaninlowerpermeabilitysands(suchascrevassesplays):ifpermeabilityishigh,theCRFincreasesslowlywithincreaseddistancefromtheperforation,indicatingthattheformationcanbeproducedfromlarger108distancesoutintothereservoirthanifthepermeabilityislow,whentheCRFwillincreasemorerapidlywithdistance.Asdiscussedintheprevioussection,CRFclusteringusesasinputthe3DGEOCAP-derivedpermeabilitymodelsforkhandkv'Thesemodels,basedonpropertymodellingwithintheconstraintsofgeneticfaciesbodies,containavalueineveryvoxel;inthisparticularmodelthevoxelsizeis100mx100mx2ft(the2ftreferstotheverticaldepthdimension).Fromeachoil-producingperforation,outwards,GEOCAPcalculatesfromvoxeltovoxeltheincreaseinCRFoverthewholemodel.Foreveryvoxel,theprogramconsidersthetensurroundingvoxels:eightinthehorizontalplane(forwhichitusesthekhvalue),thevoxelaboveandthevoxelbelow(forwhichitusesthekvvalue)andassignseachvoxelinthemodelaCRFvalueaccordingtothefollowingequation:CRF(n+1)=CRF(n)+L.\dIk(interface)Thek(interface)intheequationaboveisthepermeabilitycalculatedattheinterfaceoftwoadjacentvoxels.TheuserentersamaximumCRFfigure(CRFmax),whichtheprogramusesasaclusteringcut-offmaximum.Workingoutfromeachperforation,connectivityproceedsontosuccessivevoxelsuntilthecalculatedCRFvalueexceedstheuser-enteredCRFmax.Inthiswayclusterstotheperforationsaregenerated(Fig.4).ScenarioscanberunusingdifferentCRFmax;CRFismeasuredin[m/mD],soifCRFmaxissetatI,thismeansauniformIOOOmDsandwillseeadrainageradiusof1km.Otherfunctionalityexiststodealwithflowanisotropy,forexampleup-dip/down-dipdirectionality.Unlikemanyconnectivityfunctionalities,wheredistancemainlydeterminestowhichwellvoxelsareconnected,CRFconsidersthe'easeofflow'asthedecisivefactor.LocatingRemainingOilTargetAreasAsafirststep,thewaterinjectionandgasinjectionperforationsinthemodelweredeselectedfromtheanalysis,whilealloilproducerperforationsthathadeverproducedoilwereselected.ScenarioswererunusingaCRFmaxofI,1.5and2.IncreasingCRFmaxincreasesconnectedvolumetothewells,therebydecreasingthesizeofremainingoiltargets,reducingsometounderIMMbblsSTOlP.DecreasingCRFmaxhasthereverseeffect,increasingremainingtargetsize.AnillustrationofaresultofCRFclusteringfortwoadjacentwellsisshowninFig.4aand4bwhichclearlyshowsthedifferentarealextentoftheclustersindifferentreservoirlayers.Thesecondstepisthentoremovealltheseclusters(connectedvolumes)fromthe3Dpermeabilitymodel.Thisresultsina3Dpermeabilitymodelofunconnectedsands(Fig.5).Inordertolocatepotentialtargetareasofthemodel,GEOCAPfunctionalitywasusedtofindconnectedclustersoftheseunconnectedvoxelsthattotalledoverIMMbblsSTOlP,andthatliewithinthepresent-dayoilrims.SPE384733DGEOLOGICALMODELLINGTOLOCATEREMAININGOILTARGETSINBRENTRESERVOIR,BRENTFIELD3Thepresent-dayfluidcontactdistributionwithinthereservoiriscomplex,duetoacombinationofbothgeologicalstructureandtheproduction/injectionhistory.Themodelneededtobedividedinto8differentregions,wheregasandoilcontactswereenteredseparatelyforeachofthe17reservoirzonesusedinthemodelling.ThishasbeeneffectivelyhandledwithinGEOCAP,allowingtherapidinvestigationoftheeffectofcontactuncertainties.Asafirstcontrolstep,theCRFexercisewascarriedoutusingallwellsexistingatthetime,butnoneoftheplanned(undrilled)LTROwells.TargetswereidentifiedandthentheLTROwellswere'drilled'intothemodeltocheckthattheyactuallypenetratedanidentifiedCRFtarget.AsshowninFig.6allLTROwells(butone)penetratedaCRF-identifiedtarget;thisgaveconfidencetothemethodologyandthemodellingparameters.AtthetimeofwritingthemajorityoftheseLTROwellshavenowbeensuccessfullydrilled.ThenextstepwastorepeattheCRFanalysistoidentifypost-LTROcampaignoiltargetopportunities.Inordertodothis,theLTROwells(whichatthattimewerenotyetdrilled)wereincludedalongwiththeexistingwellsintheanalysisandtheywereassumedtobeperforatedovertheirentirelength.Theresultsshowedthatseveralsizeabletargets,eachoverIMMbblsSTOlP,willstillbeleftintheNessreservoirafterallthecurrentlyplannedwellshavebeendrilled.TheremainingoiltargetsidentifiedintheregionoftheBrentBravoplatformareshowninFig.7.ArecentstudybyBrentreservoirengineershasshownthatindependentlycalculatedCRFvaluesbasedonproductiondataareintherange1-1.5.ThepreferredCRFmaxscenariousedintheclusteringstudywasCRFmax=1.5,whichbasedontheproductiondatamaybeslightlytoohigh,inwhichcasethesizeofthelocatedtargetswouldincreasefromthatcalculated.Anotherfactortoconsiderinrespecttotargetsize,isthepermeabilitymodelswhichuserelationshipsbasedoncoreplugdataintheirderivation,asdiscussedpreviously.ThisraisesissuesofusingdatameasuredfromIinchplugstoassignvaluestovoxels100mx100mx2ft(i.e.'upscaling'fromcore-plugsizetovoxelsize).Thisismorelikelytogivepermeabilitiesinthemodelwhicharetoohigh(ratherthantoolow),whichwouldleadtomorerockvolumebeingconnectedtowellsusedintheanalysisandhencereductioninidentifiedtargetsize.Boththesefactorsacttogethertofavourincreasedconnectivitytothewellsusedinthismodellingexercise,indicatingthatpredictedtargetsmayinfactbelarger.SincetheGEOCAPmodeldoesnotyetincludethecomplexBrentslumpsarea",targetsidentifiedinthecrestofthefieldneedtobeevaluatedintermsoffaultjuxtapositionwiththeslumpsandproductionfromtheslumpwells.Newresultsfromtheinterpretationofthelatest1995seismicsurve/willalsoneedtobetakenintoconsideration.109ConclusionsandfuturestrategyTheresultsofthisstudyclearlydemonstratethepotentialvalueandimpactof3Dgeological(GEOCAP)modelling,eveninmature,denselydrilledfieldsthatarecominguptoendoffieldlife.TheresultsfromtheCRFanalysiswhichdoesnotincludetheLTROwells,showsthattheplannedwellspenetratetargetsidentifiedbythismethodology;therebygivingstrongindicationsthatthetechniquecanbeappliedinpractice.TheresultsfromtheCRFscenarioswhichincludesalltheLTROwellsandtheexistingwells,locatesseveralareasofmorethanIMMbblsSTOlPleftuntargetedintheNessreservoirafterthepresentlyplannedwellshavebeendrilled.Theseareas,thelargestofwhichareinmarineshorefacesands,arenotoptimallysituatedtobedrainedfromexistingwells(duetothepermeabilityofthesandsandtheirdistancefromaproducingwell).ThisisespeciallyimportantfortheBrentreservoir,astimeisnowoftheessence,inviewofthedepressurisationofthereservoir.Theseremainingtargetareasarenowbeingindependentlyinvestigatedfromthereservoirengineeringperspective,makingfulluseoftheverylatestsurveillancedatatominimisefluidcontactuncertainty.Possibleoptionsforthedevelopmentoftargetsthatstillpassthisscreeningprocess,suchastheperforationofexistingwellsorthedesignofnewside-tracks,canbeinvestigatedandoptimisedwithinGEOCAP.NomenclatureLTRO=LocateTheRemainingOilcampaign(1995-96)GEOCAP=Shellproprietry3DgeologicalandpropertymodellingprogramCRF=CumulativeResistancetoFlow,m/mDvoxel=gridblockofthe3Dmodelm=metresmD=millidarciesk=permeability,mDkh=horizontalpermeabilty,mDkv=verticalpermeability,mD~=viscosity,cPP=pressure,psiOx=distancefromperforationtocentreofvoxelinpermeabilitymodelCRF(n+1)=CRFvalueofstartvoxelCRF(n)=CRFvalueoftheneighbouringvoxel~d=distancebetweenvoxelmid-pointsAcknowledgmentsWethankShellU.K.ExplorationandProduction.EssoExplorationandProductionU.K.andShellInternationalExplorationandProductionB.V.,ResearchandTechnicalServices(RTS),theNetherlands,fortheirpermissiontopublishthispaper.ThisworkwascarriedoutwhilethefirstauthorwasworkingintheReservoirGeologyStudiesGroup4F.V.ABBOTS,A.VANKUIJKSPE38473inShellEXPRO.TheprojectwouldnothavebeencompletedwithinthetightdeadlinewithouttheassistanceandenthusiasmofourcolleagueandfriendthelateJefvanderVorstwhowasworkingontheStatfjordFormationGEOCAPmodellingoftheBrentFieldatthesametimethisworkwasdone.WealsoacknowledgetheothermembersoftheGEOCAP/MoResdevelopmentteaminRTSandAlexWetzelaerandColinBrucewhowereformerlyworkingintheBrentFieldUnit.SIMetricConversionFactorsbblx1.589874ftx3.048*·conversionisexactReferencesE-OI=m3E-OI=mI.Braithwaite,C.I.M.andSchulte,W.M.:"TransformingtheFutureoftheBrentField:Depressurisation-TheNextDevelopmentPhase",EuropecCannes,France,16-18November19922.Coutts,S.D.,Jurgens,M.,vanKessel,0.,Pronk,D.,andWard,V.e.:"Phase2DevelopmentoftheSlumpedCrestalAreaofthe110BrentReservoir,Brent",SPE38476,1997OffshoreEuropeConference,Aberdeen,Scotland,9-12September19973.Budding,M.e.,Ainsworth,B.,Davies,H.,Davies,P.,Fowles,1.,vanLieshout,J.,Nepveu,M.,Stulemeijer,\.J.P.:"3DreservoirmodellingwithGEOCAP",AAPGConference,Houston,USA,19944.Taylor,S.R:"3DModellingtoOptimiseProductiona
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