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SPE-0111-0046-JPT

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SPE 0111 0046 JPT
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46JPT•JANUARY2011Therecoveryefficiencybypolymerflood-ingis10%higherthanthatofwater-floodingforthemainreservoirsintheDaqingoilfield.Toenhanceoilrecoveryfurther,itisimportanttoknowhowmuchoilremainsinthereservoirafterpolymerinjectionalongwithitsdistribu-tion.Thisstudyusedloggingdatafrom200newwellsforamacroanalysisonremaining-oildistributionafterpolymerinjection.Samplesfromcoredwells,beforeandafterpolymerflooding,werestudiedbyuseofcore-membrane-fluo-rescencetechnologytoanalyzemicro-scopicremaining-oildistribution.IntroductionLarge-scalepolymerfloodinghasbeenongoingintheDaqingoilfieldsince1996.Yearlyoilproductionfromthepolymerprocesshasexceeded107tonnesfor8years.Polymerinjectionhasbecometheleadingtechnologyforcontrolingoil-productiondeclineinthefield.Fieldexperienceindicatesthattheviscosityandelasticity(viscoelasticity)ofthepolymersolutioncanincreasethesweptvolumegreatlyandenhancetheoil-recoveryefficiency,resultinginoilrecoverybypolymerinjectioninmajorreservoirsthatis10%higherthanthatofwaterflooding,butapproximately50%ofthecrude-oilvolumeremainsafterpolymerinjection.Theremainingoilcanbedevelopedbyhigh-viscoelasticity-polymerinjection,alkaline/surfactant/polymersolutions,orfoamflooding.Butfirst,characteristicsoftheremaining-oildistributionmustbedescribedaccurate-ly.Therefore,itisimportanttostudytheremaining-oildistributiontoimproveoilrecoveryfurtherandtoadjustsub-sequentpolymerinjection.Thisstudyevaluatedtheremaining-oildistribution,bothmacroandmicro,afterpolymerinjectioninthePIreservoirsoftheSZzonesoftheDaqingoilfield.MacrodistributionofRemainingOilUptoJune2010,14testblockshadcompletedpolymerinjectionandhadbegunwaterinjection.TargetintervalsofpolymerfloodingarethePIreservoirs,whicharefluvialdepositswithwide-spreadandthickoillayers.Thesandbodyconsistsmainlyofbraided-channelsand,meanderingsand,anddistributary-channelsand.ThemacrodistributionoftheremainingoilinthePIreservoirswasstudiedonthebasisoflog-interpretationdatafrominfillwellsandcored-welldata(beforeandafterpolymerflooding)fromthreetypicaltestblocks.Thestudyshowedthatafterpolymerinjection,thedistributionofremainingoilwasmorescatteredhorizontally,andtheaverageoilsaturationforthesethreecoredwellswasreducedby11.9%,from52.8%beforepolymerfloodingto40.9%afterpolymerflooding.Theflushingdegreeoftheoillayerintheverticaldirec-tionincreasedsignificantly,andaveragesweptthicknessimprovedfrom68.6%beforepolymerinjectionto89.4%afterpolymerflooding.Remaining-OilDistributionintheHorizontalDirection.Theoildistribu-tionafterpolymerfloodingwasmorescatteredinthehorizontaldirectionthanbeforeflooding.Log-interpretationdatabeforeandafterpolymerinjectioninthewesternpartoftheB1regionshowedthatafterpolymerflooding,theoilsaturationdeclinedsharplyandtheareaswithhighoilsaturationbecamesmaller,indicatingthatafterpolymerflooding,thepotentialfordrillinghori-zontalinfillwellswasless.Theremain-ingoilinthehorizontaldirectionwasdistributedmainlyinlow-permeablilityreservoirs,ontheedgeofthesandbody(e.g.,atafaultorpinchoutboundary),oralongadistributaryline,andintheplaceswheretherelationbetweentheinjectionandproductionwasimper-fect,whichistheresultofpermeabilityvariationandwelllocation.Forhigh-er-permeabilityreservoirs,theinjectedvolumeofpolymersolutionandthesweptvolumewerehigh,resultinginlessremainingoil.Forreservoirswithlowerpermeabilityorthatareclosetotheedgeofthesandbody,theinjectedvolumeofpolymersolutionandsweptvolumeofthereservoirwereless,lead-ingtomoreremainingoil.Therecoveryefficiencyofpolymerinjectionintochannelsandismuchhigherthanthatforinjectionintoothersandbodies.Becausechannelsandismorehomogeneousandhasfavorablephysicalproperties,itiseasyforapoly-mersolutiontomovethroughthereser-voir,resultinginhighsweptvolumeandhighdisplacementefficiency.Afterpoly-merflooding,recoveryfromindividualsedimentaryunitsaveraged50.63%.Fornonchannelsands,withpoorerphysicalpropertiesandmuchhigherheterogene-ity,itisdifficultforthepolymersolutiontoflowintothereservoir;therefore,thesweepanddisplacementefficienciesareworse.Afterpolymerinjection,averagerecoveryfromindividualsedimentaryunitswasonly38.63%.Thisarticle,writtenbySeniorTech-nologyEditorDennisDenney,con-tainshighlightsofpaperSPE133808,“StudyonRemaining-OilDistributionAfterPolymerInjection,”byJiechengCheng,SPE,DaqingOilFieldCom-pany;JianguangWei,DaqingOilFieldCompanyandChinaUniversityofPetroleum;KaopingSong,SPE,NortheastPetroleumUniversity;andPeihuiHan,SPE,DaqingOilFieldCompany,preparedforthe2010SPEAnnualTechnicalConferenceandExhibition,Florence,Italy,19–22September.Thepaperhasnotbeenpeerreviewed.StudyofRemaining-OilDistributionAfterPolymerInjectionEORPERFORMANCEANDMODELINGForalimitedtime,thefull-lengthpaperisavailablefreetoSPEmembersatwww.spe.org/jpt.JPT•JANUARY201147Remaining-OilDistributionintheVerticalDirection.Afterpolymerflood-ing,thepercentageofflushedreservoirimprovedgreatly.Beforepolymerinjec-tion,15.8%ofthethicknessoftheres-ervoirremainedunsweptwithapproxi-mately8-mthicknessofthePI2reservoirundeveloped.Afterpolymerinjection,theunsweptthicknesswasonly1.0%ofthereservoirandthePI2reservoirwasflushedcompletely,indicatingthatpoly-merinjectionincreasedreservoirflush-ingsignificantly.Afterpolymerflooding,thepercentagesofhigh-andmedium-flushedreservoirincreasedfrom29.2to40.4%andfrom28.2to42.1%,respec-tively,andthepercentageoflow-flushedandunsweptreservoirdroppedfrom26.8to16.5%andfrom15.8to1.0%,respectively,demonstratingthatpoly-merfloodingcanimproveinjectivity/flu-id-productionprofilesgreatlytoincreasethesweptvolume.Intheverticaldirection,thedistri-butionsoflow-/not-watered-outzonesandmedium-/highly-watered-outzonesweremixed.Thewatered-outdegreewashigheratthetopofthezoneandloweratthebottom.Remainingoilwashighatthetopofeverysequenceandinthinpoorreservoirswithlowerperme-ability.Thehighly-watered-outzonesweredistributedmainlyatthebottomofathickoillayer.Therewereareasinwhichtheremainingoilafterpoly-merfloodinghadnogreatchange(oilsaturationbeforepolymerinjectionwasverylow,averaging31.7%),andtherewereareasofremainingoilafterpoly-merfloodingthathadgreatchange(mediumwateredoutbeforepolymerflooding,followedbyhighlywateredoutafterpolymer-solutioninjection).Mostmedium-watered-outzoneswereinthemiddleofintervals,whilemostoftheunsweptpartsweredistributedatthetopofindividualsedimentaryunits.Insomeareas,thereservoirwasnotaffect-edbywaterinjectionorbythepolymerprocess.Inotherareas,theoilwassweptbywaterfloodingbutunsweptbypoly-merflooding.Wheretheporechannelisnarrow,watercanbeinjectedthroughit,butitisdifficultforthepolymersolu-tiontoenterthereservoir.Accordingtostatisticalresultsregard-ingsweepingstatusforcoredwells,beforepolymerflooding,thepercentagesofunsweptreservoirswiththickness2mwere18.3and81.7%,respectively.Afterpolymerinjection,thepercentagesofunsweptreservoirswiththickness2mwere27.1and72.9%,respectively,indicatingthat10.6%ofunsweptreservoirisdistributedmainlyinthickoillayerswiththethick-nessgreaterthan2m.MicrodistributionofRemainingOilDatacollectedfromcoredwellsB1-6-J27andB1-6-J26,beforeandafterpolymerflood,wereanalyzedbyuseofcore-membrane-fluorescencetech-nologytostudymicrodistributionofremainingoilforthesamewellgroup.Thefluorescenceexperimentsshoweddifferentkindsofremainingoilbeforeandafterpolymerinjection.Followingpolymerflooding,thetypesofmicro-remainingoilweresimilartothoseafterwaterflood,whicharecontrolledmainlybycapillaryforce.Forcoresfloodedbypolymersolution,differentkindsofremainingoilwerereducedaccordingtorockmatrix.Cluster-typeresidualoil,whichwasaffectedgreatly%F(PMZFSBOE.BD/BVHIUPO4QSJOH7BMMFZ3PBE4VJUF&BTU5PXFS%BMMBT5FYBT0öDF'BY%&(0-:&3."$/"6()50/"/%803-%8*%&1&530-&6.$0/46-5"/54%"--"4)06450/.04$08$"-("3:3ERVINGTHE/ILAND'AS)NDUSTRY3INCEXXXEFNBDDPNEFHPMZFS!EFNBDDPN'PS)PVTUPOPöDF'PS.PTDPXPöDF'PS$BOBEJBOPöDF48JPT•JANUARY2011bythefrictionofpolymersolution,wasreducedsignificantly.Theresidualoilatthedeadend,whichwasaffectedlessbythefrictionofpolymersolution,wasdecreasedslightly.Foroilcolumnandoildroplet,thereductionofresidualoilwastheleastbecausethefrictionofpolymersolutionactingonresidualoilwastheleastandtheresidualoilwasblockedbyunconnectedpores.Remaining-OilDistributionforDif-ferentWateredZones.Withwateredextentdecreased,microscopicoilsatura-tionswithallkindsofremainingoilareincreased,butincreasingextentsaredif-ferent.Inhighlywateredzones,film-likeandcluster-typeremaining-oilsatura-tionwasverylow,averaging4.02%,andremaining-oilsaturationofoilcolumn,oildroplet,andatthedeadendalsowasverylow,averaging10.97%.Inmedium-wateredzones,film-likeandcluster-typeremaining-oilsaturationwas3.93%high-erthanthatofhighlywateredzones,andtheaveragevaluecanreach7.95%.Theremaining-oilsaturationofoilcolumn,oildroplet,andatthedeadendincreasedby11.09%andaveraged22.06%.Therecoveryefficiencywaslesseffec-tiveinlow-watered-outzones,wheretheporechannelsarenarrowandcapil-laryforceishigh,resultinginlesspoly-mersolutionbeinginjected.Therefore,inlow-watered-outzones,thefilm-likeandcluster-typeresidual-oilsaturationincreasedgreatlyandreached18.22%,10.27%higherthanthatinmedium-watered-outzones,andresidual-oilsatu-rationoftheoilcolumn,oildroplet,andatthedeadendaveraged37.78%,increasing9.72%.Thedistributionofmicroscopicremainingoilafterpolymerfloodcanbedividedintotwokinds.Oneistheremainingoilunrecoveredbywater-flood,which,afterpolymerinjection,remainsunrecovered.Theotherkindisremainingoilrecoveredbywaterinjec-tionbutnotdisplacedbypolymerflood.Thefirstkindofremainingoilreferstothecrudeoiltrappedbysecondarycementationorindeadpores,orreferstotheoilthatexistsinthereservoirsthatthewaterflooddoesnotsweep.Thisremainingoilcannotberecoveredbywaterfloodorbypolymerfloodunlessothermeasuresaretaken.Theresultsgainedfromtwogroupsoffluorescenceexperimentsindicatethatresidualoilindeadporesafterwater-floodoccupies4.78to5.96%oftheporespace,whileafterpolymerflood-ing,residualoilindeadporesreached5.79to11.44%oftheporespace.Thesecondkindofremainingoilistheoilunrecoveredbypolymerflood,whichresultsfromunsweptporevolumebythepolymer.Becauseporechannelsarenarrow,watercanbeinjectedintothechannelsbutitisdifficultforpolymersolutiontoenter.Inhigh-permeability-core-displacingexperiments,thesecondkindofremainingoilseldomexists,butthereisalargeamountofitinrealreservoirs.ConclusionsAfterpolymerinjection,distributionofthehigherremaining-oilsaturationwasscattered,mainlyinphase-bound-ary,pinch,andfaultareas;closetothedividinglinebetweentwomicro-phases;andalongdistributarylines.Theaverageremaining-oilsaturationwas4.4%higherthanthatalongmain-streamlines.JPTSocietyofPetroleumEngineersReservoirSIMULATIONSYMPOSIUM21–23February2011TheWoodlands,Texas,USATheWoodlandsWaterwayMarriottHotel&ConventionCenterRegisternowwww.spe.org/events/rssPleasevisittheUniversityofNorthDakotaAffirmativeActionWebsiteformoreinformation:http://www.und.edu/dept/aao/newengineerjob.htmTENURE-TRACKASSISTANT,ASSOCIATE,ORFULLPROFESSORPOSITIONINPETROLEUMENGINEERING
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