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Accurate Determination of Remaining Oil Saturation 精确测量剩余油饱和度的方法(ROS)局限性和优势

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Accurate Determination of Remaining Oil Saturation 精确 测量 剩余 饱和度 方法 ROS 局限性 优势
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20thWorldPetroleumCongress,Doha2011Forum09:Breakthroughsinsubsurfaceimaginganddirecthydrocarbondetection©WorldPetroleumCouncil1AccurateDeterminationofRemainingOilSaturation(ROS):ChallengesandTechniquesMrKhaledSubai,SaudiAramco,SaudiArabiaMrAhmedAl-Harbi,SaudiAramco,SaudiArabiaAbstractSaudiAramco,theworld'sleadingpetroleumenergyprovider,hasalonghistoryindeployingreservoirsweepmonitoringtechnologiestoensuremaximumoilrecoveryefficiencyatthedesiredproductionrates.DeterminationofthesweepefficiencyandRemainingOilSaturation(ROS)isimportantandsetstheeconomicalbasisforfuturework-overandEORprojects.AccuratedeterminationofROS,particularlyinwaterfloodedareas,isextremelydifficultduetonotabledifferencesinsalinitybetweentheoriginal(connate)waterandinjectedwater.Toovercomethischallenge,SaudiAramcohasadopteddataacquisitionprogramsthatincludein-situmeasurementsinsensitivetowatersalinityandfluiddisplacementprocesses.ThesetechnologiesincludeNuclearMagneticResonanceinLog-Inject-Logmode,Carbon/Oxygen,andDielectriclogs.ResultsfromwelllogsareroutinelycalibratedwithdatafromWire-lineformationtestersandspecialcoreanalysis.ROSresultsfromthedifferentmethodsarequalitycheckedandintegratedtoproducereliablefigures.ThispresentationhighlightsSaudiAramco'sROSacquisitionprograms,includinglimitationsofthesetechnologies.ThepresentationalsodiscussesongoingeffortstofurtherreducetheuncertaintiesinfutureROSmeasurements.20thWorldPetroleumCongress,Doha2011Forum09:Breakthroughsinsubsurfaceimaginganddirecthydrocarbondetection©WorldPetroleumCouncil2123MicroscopicInjectorProduce231MacroscopicBCBypassedCapillaryPressureConnateWaterResidualOilSOR0100%ImbibedROSMax-+AROS@timeXROS=SORSw231IntroductionOilproducingcompaniesusuallyestimatetheoriginalvolumeofoilinplaceattimezerobeforetheyinitiateproduction.Aftertheystartproducingtheoil,theyroutinelymonitorthepercentageofoilremaining.Thisremainingpercentageatagiventimeisgenerallytermedremainingoilsaturation(ROS).Thisprocesscontinuesuntilalltheoilthatcanbeproducedthroughconventionalmethods,likewaterflooding,hasbeenachieved.Atthistime,theremainingoilisreferredtoasresidualoilsaturation(Sor).Notionally,thevalueofROScanbeaslowasSor;butusuallyitisgreater.Atthemicroscopicscale,viscousandcapillaryforcesarethemainopposingforces,governinganyimmiscibledisplacementprocess.Displacementprocessesarecarefullyengineeredtomaximizeviscousforceswhileminimizingcapillaryforcestoenhancedisplacementefficiencyandmaximizeoilrecovery.Theseforcesarelargelydictatedbyinterrelatedreservoirattributes:wettability,porestructureandfluiddynamics.Muchresearchhasbeendonetoinvestigatethefluiddistributionsanddisplacementmechanismsandtheinterplayoftheseattributesandforcesatthemicroscopiclevel.Atthemacroscopiclevel,reservoirstructureandfeatures,e.g.,fault,fractures,barriers,strataforms,heterogeneities,makereservoirsgeologicallycomplex.Coupledwithproduction/injectionfluidflowdynamicsandeffectsofgravity,thesemultidimensionalcomplexitiesdominatefluidmovementwithinthereservoirand,therefore,resultincomplexfluiddistributions,bothverticallyandlaterally.Adiagrammaticdemonstrationofthedisplacementprocessatbothscales:microscopicandmacroscopic,ispresentedinFig.1.Figure1.Schematicofthedisplacementprocess:SaturationCondition1(ingraphsA,BandC)istheinitialoilsaturationbeforeexperiencinganycontactwithinjectedoraquiferwater;thisrepresentsthemaximumrangeforROS.Condition2isjustaheadofthewaterfrontwithsomewatersaturationincrease(dependingonreservoirwettabilityandtheappliedrateofwaterflooding)byspontaneousimbibition(Ma,etal.,1996).Condition3isattheresidualoil,i.e.,allmovableoilhasbeendisplacedwithwater;therebyROSequalsSor.Atthemacroscopicscale,reservoirfeatures,suchasfracturesorbarriersmayresultinbypassedoilzones/intervals,areasthatareneverincontactwithwaterandyetbehindthewaterfront.20thWorldPetroleumCongress,Doha2011Forum09:Breakthroughsinsubsurfaceimaginganddirecthydrocarbondetection©WorldPetroleumCouncil3Quantitativeknowledgeofthespatialfluiddistributionisakeyinputinthedecisionmakingprocessofreservoirmanagementstrategiestoproactivelyenhancethesweepefficiencyandfloodfrontconformance.Italsodefinestheopportunitywindowforfutureenhancedoilrecovery(EOR)projects,whichcanbeeconomicallymarginal.Ahighdegreeofaccuracyofremainingoildistributionisverydesirable.Allnecessitatetheneedfordeploymentofdataacquisitionstrategiesandbestpracticesatdesirablefrequenciesandlocations,notonlyatthematurestage,butalsoattheearlyproductionlifeofthefield.ThesignificanceofROSisevidencedbythespectrumofdeterminationtechniquesthathasbeendeployedoverthepast40yearsandreviewedextensivelyintheliterature.Determinationtechniquescanbesummarizedinto:(1)materialbalance,(2)coreanalysis,(3)single-welltracerstests,(4)pressuretransienttests,and(5)wirelineloggingtechniques.Thetechniquesunderthewirelinelogging,whicharethefocusofthispaper,includeresistivity,pulsed-neutroncapture,pulsedneutronspectral(Carbon/Oxygen(C/O)),nuclearmagneticresonance(NMR)anddielectric.ThispaperputsmoreemphasisontheNMRanddielectricdataacquisitionforROSdeterminationapplicationsandhighlightsthemainadvantagesandchallengesoftheserecenttechnologies,withfieldexamplesfromcarbonatereservoirs.Resistivity-basedMethodResistivity-basedsaturationmodels,suchasArchieandnon-Archiemodels,havealwaysbeenthepreferredtechniquesforwatersaturationcalculationsbecauseoftheirreliability,deeperdepthofinvestigation,andcosteffectiveness.Inusingresistivitymeasurementforreservoirsurveillance,themainfactorsthataffecttheaccuracyofwatersaturationareArchieexponents(mandn)andthesalinityoftheconnatewater(Rw).Thistraditionaltechnique,however,canbeimpairedbythefollowing:Drainage-ImbibitionResistivityHysteresis:Similartoothermultiphasereservoirpetrophysicalproperties,suchascapillarypressureandrelativepermeability,resistivitymeasurementisdisplacementprocessdependent.Itdisplaysadrainage-imbibitionhysteresisphenomenon.Thiscanmaketheinterpretationofresistivitylogswithdrainage-imbibitionhysteresischallenging.First,itisdifficulttorecognizeintervalswhereanimbibitionprocesshasstarted,inparticularfornewlydrilledwellsinfloodedareas.Logsinobservationwellsarerelativelyeasiertointerpretifagoodbaselineresistivitylogisavailablefortime-lapseanalysis.Second,duetothisdrainage-imbibitionhysteresis,Archiesaturationexponentusedinwatersaturationcalculationsfordrainageisdifferentfromthatofimbibition.Historically,electricalrockpropertiesmeasuredbyoperatingcompaniesintheirownlaboratoriesorincommerciallaboratoriesaremostlydrainagesaturationexponents.Unlikedrainagesaturationexponentdata,imbibitionsaturationexponentisrarelyavailableandismuchmoredifficultandtimeconsumingtoobtain.MixedFormationWaterSalinity:Connatewatersalinityorresistivityisakeyparameterthataffectsresistivityderivedsaturation.Inzonesofareservoirthathavebeensweptbywater,salinitycanbequitedifferentfromoriginalformationwater(connatewater)andthiscontrastmightintroducesignificanterrorsinthecalculationofsaturations.Longproductionandinjectionhistory,andcomplexgeologymakesalinityprofileshardtopredict.Toimprovetheaccuracyofwatersaturationsurveillance,distributionofformationwatersalinity,spatiallyandvertically,SaudiAramcoextensivelyperformsroutinewatersampling.ALog-Inject-Log(LIL)procedure,devisedbyMurphy(1973),wasanattempttoincreasethereliabilityofresistivity-basedoilsaturation.Thespecialprocedureinvolvesrunningabaseresistivitylog,Rt(Sw),followedbyseveralinjectionstepswithsolventtodisplaceallremainingoilandtheninjectionofformationwaterwithaknownresistivity,Rw,andfinallyre-loggingresistivity,Rt(Sw=1)=Ro.Withthisprocedure,formationwatersalinityinformationisavailable,butnotnecessarilyneeded.Thesaturationexponentisneededandalsoinformationonhowitmightbealteredaftertheinjectionprocess.Theaccuracyofthisprocedurereliesheavilyon20thWorldPetroleumCongress,Doha2011Forum09:Breakthroughsinsubsurfaceimaginganddirecthydrocarbondetection©WorldPetroleumCouncil4theeffectivenessoftheinjectionprocessandthemiscibledisplacementoftheremainingoil,whichcanbequitechallenging.NuclearMagneticResonance(NMR)NuclearMagneticResonance(NMR)technologywasfirstintroducedforROSapplicationbyRobinsonetal.,(1972and1974).ThemainadvantageofNMRistheindependenceitoffersfromwatersalinityandsaturationexponent.TheNMRtechnologymeasuresrelaxationtimes,whichtendtooverlaptheoilandwatersignalsinaporespace,hinderinganyidentificationorobviouslyanyquantificationefforts,Fig.2a.Therefore,Robinsondevelopedaprocedurethatresultsinsplittingthewatersignalfromtheoilsignalintherelaxationtimedomain,allowingquantificationofremainingoil,Fig.2b.ThisprocedureiswhatisknownintheindustryasdopingorLIL.Achemicalmaterialmanganesechloride(MnCl2)isaddedtothedrillingfluidbeforedrillingthezonesofinterest.Whenitinvadestheformationduringthedrillingprocess,theparamagneticionMn++dissolveonlyinthewaterandshortensitsrelaxationtime,shiftingitawayfromoilthatremainsunchanged.Concentrationofthedopantshouldbecarefullydesignedtowidenenoughthesplitbetweenoilandwater;butnottooshortthatitgoesbeyondthetoolsdetectablelimits.Figure2.TypicalNMRmeasurementsbeforeandafterdoping.PlotAshowsNMRrelaxationtimebeforedoping,thebaselog,givenporesizedistributionandirreduciblewaterinformation;oilandwatersignalcannotbedifferentiatedastheytendtooverlap.PlotBdemonstratestheeffectofthedopingprocessontheNMRsignal:aclearshiftinwatersignalfromtheoilsignal;therefore,oilvolumecanbecomputedafterapplyingasimplecutoff.Arelaxationtimecutoffislaterappliedtoquantifythevolumesofwaterandoil.Liketheinjectionprocedurefortheresistivity-basedapproach,theaccuracyofROSfromtheNMRapproachisdeterminedbythesuccessofthedopantinjectioninseparatingthewaterandoilsignals.DielectricDielectrictechnologyhasalonghistoryofdevelopment,sinceitsearlyintroduction(Calvertetal.,1977).Advancesintechnology,tooldesignandsoftwarehavegivenrisetoimprovementmanifestedinthenewgenerationofdielectrictools(Schmittetal.,2011).SimilartoNMRtechnology,thedielectrictoolprovidessolutionsthatareindependentofwatersalinityandsaturationexponent.Itisadirectmeasurement.Nospecialprocedureisrequiredpriortologging,suchas,dopingfortheNMR.Itmeasureswater-filledporositynearthewellbore.Thedielectricmeasurementisbasedontheelectromagneticwavepropagationinporousmediathatisgovernedbyconductivityanddielectricpermittivity.DielectricpermittivityofwaterstandsoutamonganyothercommonmineralsorfluidsinpetroleumsystemsasshowninTable1.Thisphysicalphenomenonfeaturesthedielectricmeasurementstobesensitive20thWorldPetroleumCongress,Doha2011Forum09:Breakthroughsinsubsurfaceimaginganddirecthydrocarbondetection©WorldPetroleumCouncil5onlytotheaqueousphase.Therefore,coupledwithtotalporosityinformationandmatrixpermittivity,oilsaturationininvadedzonescanbecalculated(Schmittetal.,2011).MaterialPermittivityQuartz4.4Sandstone4.65Limestone7.5to9.2Dolomite6.8Clay(drycolloids)5.0–5.8Anhydrite6.4Halite5.9Gypsum4.16Oil2.2Air,Gas1Water*50-78*Dependentonfrequency,pressure,temperatureandsalinityTable1.Reservoirmineralandfluidrelativedielectricpermiativity.FieldExampleThissectiondiscussesafieldexamplefromaSaudiAramcofieldthatisunderwaterflooding.Overtheyears,waterwithdifferentsalinitieshasbeeninjectedforpressuremaintenance.Togetherwithoriginalformationwater,allhaveresultedinamixedsalinityenvironmentrangingfrom230kppmtoaslowas10kppm.Thesubjectreservoiriscarbonate;mainlylimestonewithlocalizeddolomitization.Thereservoirqualityrangesfromhighlyporousandpermeablegrainstonesatthetop,degradingdownwardtotightfaciesmudstonesandwackestonesatthebottom.Inthefollowingexamples,allthewellsarelocatedbehindthefloodfronts,insweptareas,andnearwaterinjectors.TheLILprocedurewasused.Thewellwasdrilledwitha8½”bitsizeandconventionalmudacrosstheinterestzone.ThisholesectionwasthenloggedwithtriplecomboforbasicformationevaluationandalsoNMRforporesizedistribution.Subsequently,theholewasunderreamedtoa10”holesizewithmuddopedwithMnCl2ataconcentrationof1.59lb/bbl.Theunderreamingstepisessentialtoremovethemudcakeandallowthedopanttoinvadenearwellboreandmixwiththewater.Themuddensitywascarefullydesignedtoallowslightlyoverbalancedrilling,typicallynotmorethan500psitoavoidstrippingtheoilfromthenearwellboreregion.Afterenlarginganddopingthewell,theNMRwasrunagain.Figure3showstherelaxationtimeT2beforeandafterdoping.Aclearshiftinthewatersignalcanbeseeninthe“afterdoping”relaxationtime.AT2cutoffwasapplied,andremainingoilvolumeandsaturationwerecomputed.Additionally,thenewdielectrictechnologywasutilizedforROSapplicationandcomparedwithNMR-LIL.Dielectricwasrunbeforeandafterdopingtoensurethattherewerenoartifactsonthedielectricmeasurements.Figure3showstheplotofROSfromthedielectricmeasurements.Dielectricmeasuresthewaterfilledporosity,whichisthendisplayedalongsidetotalporosityfromformationevaluationanalysis.ROScomputedfromNMRanddielectricshowedaverygoodmatch.Asubsequentwirelineformationtester(WFT)runindicatedwaterpressuregradient,andwatersampleswerecollected.Inthiswell,theROSfromNMRisprobablyneartheSORvalues,condition3inFig.1.Additionally,collectedwatersamplesbyWFTwereanalyzedatthelaboratoryforsalinitymeasurements.Thesesalinitydatawereusedlatertorefinetheresistivitybasedsaturationcalculation.Thewatersalinityinformationisalsousefulfor20thWorldPetroleumCongress,Doha2011Forum09:Breakthroughsinsubsurfaceimaginganddirecthydrocarbondetection©WorldPetroleumCouncil6understandingtheregionalfluiddisplacementsandasbestestimateforfutureresistivitybasedsaturationcalculation.Figure3.AfieldexampleofNMRLILanddielectriclogs.Track#2and#3showtheNMRrelaxationtimes(T2)beforeandafterthedoping.NMRandDialectricremainingoilandwatervolumesaredisplayedinTracks#4and#5,respectivly.Track#6showscomparisonbetweenROSfromNMRanddielectric.ROSDataAcquisitionStrategiesCommencingROSevaluationactivitiesduringtheearlylifeofthereservoirdevelopmentiscriticalforfutureeconomicplanning.Atearlytimesoftheproduction,ROSwillbeequivalentorneartheinitialoilsaturation,Soi.Subsequently,ROSmonitoringwithtime-lapsedataacquisitionisextremelyvaluableasthisinformationwillbeneededatlaterstagesforsecondaryreservoirdevelopmentdecisions.SaudiAramcohasanextendedhistoryofestablishinglong-termdataneedsearlyinthereservoir’slifecycle.ROSassessmentbestpracticesandfit-for-purposedataacquisitionstrategiesaredeployedforoptimalreservoirmanagementprograms.Periodicallyobservationwellsaredrilledacrossthefieldandbehindwaterfloodfront,insweptorpartiallysweptareas.Aswaterfloodfrontmoves,newobservationwellsarecontinuallyplannedtotrackthefloodfrontadvancement.EstablishedROSprofilesfromopenholelogsareusedasbaselineforsubsequentreservoirmonitoringbythedifferenttechniques.Basicwelllogsarealwaysrunforformationevaluation.ForROSdetermination,dielectric,NMR(inLILorILmodes),andpulsedneutron20thWorldPetroleumCongress,Doha2011Forum09:Breakthroughsinsubsurfaceimaginganddirecthydrocarbondetection©WorldPetroleumCouncil7(sigmaand/orC/O)arethemainin-situtechnologies,withmorefocuslatelyonthedielectricforitsuseinreservoircharacterizationandcosteffectiveness.PulsedNeutron(PN)andproductionloggingaregenerallyusedforshortertermobjectiveslikeworkoverdecisionsandoperationalplanning.Dielectric,NMR,andPNhaves
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本文标题:Accurate Determination of Remaining Oil Saturation 精确测量剩余油饱和度的方法(ROS)局限性和优势
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