油藏工程英語

ReservoirEngineeringLecturer:Tian

ShubaoFacultyofOil&GasEngineeringPetroleumUniversityofChina,BeijingUsefultipsforreadingyourprofessionalpapers/articlesUseyourrelevantprofessionalknowledgeandcommonsensetohelpyouunderstandeachparagraph;Ifyourunderstandingconflictwithrelevantprofessionalknowledge,eitheryouorthearticleiswrong,checkitagain.Understandingeachsentenceandparagraphprecisely,butexpressthemflexiblyingoodprofessionalChinese.TeachingmethodforeachtextReviewsomerelevantprofessionalknowledge.Textreading,explanationandunderstanding.Relateddiscussions.Summarythetextwith80–100words.MainPointsFluidContentoftheReservoirDefinitionandCausesofWettability

WettabilityInfluenceonMultiphaseFlowEffectsofSaturationStatesonPermeabilityReservoirHeterogeneityTypesofReservoirHeterogeneityGasandCondensateReservoirsFluidContentoftheReservoirAlthoughthestructuraltrapsinwhichoilaccumulatesexistinvariousforms,theoilusuallyoccursinassociationwithgasandsaltwater.However,someinterstitialwaterisalwayspresentintheoilzone.Whereaconsiderablevolumeofwaterunderlinestheoilinthesamesedimentarybeditisreferredasthe“aquifer”andbeingunderpressurealso,itcontributestothetotalenergyofthereservoir.FluidContentoftheReservoirTheoilitself,whenunderpressure,containsappreciablequantityofdissolvedgas.Theactualamountofgaswillbegovernedbythepressureandtemperatureinsidethereservoir,andtheoilissaidtobe“saturated”ifitcannotdissolvemoregasundertheseparticularpressureandtemperatureconditions.Ontheotherhand,theoilissaidtobe“unsaturated”ifitcoulddissolvemoregasatthesamepressureandtemperature.FluidContentoftheReservoirInmanycasestherecanbemoregasinthereservoirthantheoiliscapableofholdinginsolution.Thisextragasbeinglighterthantheoilwillhaveformeda“gascap”abovetheoilaccumulation.Ifthepressureofasaturatedoilreservoirisreducedforanyreason,gaswillcomeoutofsolutionand,thisisanimportantfactorintheproductionofoilfromthereservoir.FluidContentoftheReservoirThereservoircrudemayrangefromaveryheavyviscousoil(i.e.thick),containinglittleornodissolvedgasunderverylowpressure,toanextremelylight,thin,straw-colouredoilcontainingalargeamountofdissolvedgasunderconsiderablepressure.Theviscosityoftheoildependsroughlyonitsgravityandalsotoalargeextentonthequantityofgaswhichitholdsinsolution.Thelessviscousanoilis,andthemoregasithasinit,themorereadilywillitflowthroughtheintersticesoftherockintothebottomofthewell.FluidContentoftheReservoirJargon(professionalvocabulary),Jerstitialwater(connatewater),aquifer,Dissolvedgas,saturatedoil,unsaturatedoil,gascap,reservoircrudeFluidContentoftheReservoirDiscussionsCanyonalwaysfindtheaquiferinareservoir?Why?Sometimesgasaccumulationdoesnotoccurwithoil,isittrue?Why?Theconditionofthereservoircrudeisusuallycomplicated,isn’tit?Why?Whatisthefluidcontentofthereservoir?Whatarethestatusesofsaltwaterinthereservoir?Whatarethesituationsofgasexistsinthereservoir?DefinitionandCausesofWettabilityWettabilityisatermusedtodescribetherelativeattractionofonefluidforasolidinthepresenceofotherimmisciblefluids.Itisthemainfactorresponsibleforthemicroscopicfluiddistributioninporousmediaanditdeterminestoagreatextenttheamountofresidualoilsaturationandtheabilityofaparticularphasetoflow.Therelativeaffinityofarocktoahydrocarboninthepresenceofwaterisoftendescribedas“water-wet”,“intermediate”,or“oil-wet”.DefinitionandCausesofWettabilityWettabilitymayberepresentedbythecontactangleformedamongfluidsandaflatsolidsurfaceortheangleformedbetweenthefluids’interfaceandaglasscapillarytube.

DefinitionandCausesofWettabilityUnderstandingthecausesofwettabilityrequiresastudyofthechemistryofthefluids,thepolarityandmolecularweightofreservoirhydrocarboncompounds,andtheoccurrenceofsurfacechemicalprocessesattheoil-fluidinterface.DefinitionandCausesofWettabilityJargon

(professionalvocabulary),Jargonisthetechnicalterminologyofanyspecialisedfield.Wettability,immisciblefluids,porousmedia,residualoil,saturation,hydrocarbon,capillary,polarity,molecularweightDefinitionandCausesofWettabilityDiscussions

Pleasedefinethewettabilityinyourownwords.Whatarethecausesofwettabilityinareservoir?Whatisthesignificantinfluenceofthewettabilitytoareservoir’sproduction?WettabilityInfluenceonMultiphaseFlowThemicroscopicdistributionoffluidsinaporousmediumisgreatlyinfluencedbythedegreeofrockpreferentialwettability.Inastronglywater-wetreservoir,mostofthewaterresidesindead-endporesinsmallcapillaries,andonthegrainsurface.Instronglyoil-wetreservoir,waterisinthecentreofthelargeporesasdiscontinuousdroplets,whileoilcoatsthesurfaceofthegrainsandoccupiesthesmallercapillaries.

WettabilityInfluenceonMultiphaseFlowUnderstronglywater-wetconditionstheeffectivepermeabilitytothenon-wettingphaseatirreduciblewatersaturationisapproximatelyequaltotheabsolutepermeabilityoftherock.Ontheotherhand,instronglyoil-wetsystems,theeffectivepermeabilitytooilatirreduciblewatersaturationisgreatlyreducedbythewaterdropletsinthelargerpores.WettabilityInfluenceonMultiphaseFlowInstronglywater-wetreservoirs,watertrapsoilinthelargerporesasitadvancesalongthewallsofthepore,whileinstronglyoil-wetreservoirs,watermovesinlargerporesandoilistrappedclosetothewallsofthepores.

圖8—31“渠道流態(tài)”示意圖——濕相驅(qū)非濕相

圖8—34親油巖石注水過程中的油水分布

WettabilityInfluenceonMultiphaseFlowThepetroleumindustryhaslongrecognisedthatthewettabilityofreservoirrockhasanimportanteffectonthemultiphaseflowofoil,waterandgasthroughthereservoir.WettabilityInfluenceonMultiphaseFlowSomeinvestigationhasfoundthatrelativepermeabilitybecomeprogressivelylessfavourabletooilproductionasarockcomeslesswater-wet.Theresidualoilsaturationincreasesasarockbecomeslesswater-wet.Otherhaveshownthatweaklywater-wetcoreshavemorefavourablerelativepermeabilitycurvesandlowerresidualoilsaturationthanstronglywater-oroil-wetrocks.WettabilityInfluenceonMultiphaseFlowConceptually,thislaterbehaviourseemsreasonablesincethecapillaryforcesinstrongwater-wetcoresarestrong.Theoilmaybebypassedandtrappedinlargerporesbythetendencyofawater-wetcoretoimbibewaterintothesmallercapillaries.WettabilityInfluenceonMultiphaseFlowThebypassedoilinthelargerporesisthensurroundedbywaterandisimmobileexceptatveryhighpressuregradients.Thesaturationintervalfortwo-phaseflowunderthisconditionisprobablyshort.WettabilityInfluenceonMultiphaseFlowAsthecapillaryforcesarereducedbyreductioninpreferentialwater-wettabilityofarock,thetendencytowardrapidimbibitionaltrappingofoilinlargerporesbymovementofwaterthroughsmallporesshouldalsodiminish.Thezoneoftwo-phaseflowshouldbecomebroaderandoildisplacementtoalowerresidualsaturationshouldbepossible.WettabilityInfluenceonMultiphaseFlowIfotherfactorsremainconstant,higherflowratesandlowerinterfacialtensionsareconductivetohigheroilrecovery,thesearechangesthatdiminishtheratioofcapillaryforcestoviscousforces.EffectsofSaturationStatesonPermeabilitySaturationisatermusedtodescribetherelativevolumeoffluidsinaporousmedium.Atlowsaturationofthefluidthatpreferentiallytendstowetthegrainsofarock,thewettingphaseformsdoughnut-shapedringsaroundthegraincontactpoints.Thesearecalledpendularrings.Theringsdonotcommunicatewitheachotherandpressurecannotbetransmittedfromonependularringtoanother.Sometimessuchadistributionmayoccupyanappreciablefractionoftheporespace.Theamountdependsuponthenatureandshapeofindividualgrains,distribution,aswellasdegreeandtypeofcementation.

圖8—34親油巖石注水過程中的油水分布

EffectsofSaturationStatesonPermeabilityAbovethecriticalwetting-phasesaturation,thewettingphaseismobilethroughatortuouspathunderapressuredifferentialandasthewetting-phaseincreases,thewetting-phaserelativepermeabilityincreasesaswell.Thewetting-phasesaturationdistributioninthisregioniscalledfunicularanduptoapoint,therelativepermeabilitytothewetting-phaseislessthantherelativepermeabilitytothenon-wettingphaseduetotheadhesionforcebetweenthesolidsurfaceandwettingfluid,andthegreatertortuosityoftheflowpathforthewettingphase.EffectsofSaturationStatesonPermeabilityThenon-wettingphasemovesthroughthelargerporeswithinthisrangeofsaturation,butasthesaturationofthewettingphasefurtherincreases,thenon-wettingphasebreaksdownandformsadiscontinuousphaseatthecriticalnon-wettingphasesaturation.Thisiscalledaninsularstateofnon-wettingphasesaturation.EffectsofSaturationStatesonPermeabilityFluidflowstudieshaveshownthatwhenimmisciblefluidsflowsimultaneouslythroughaporousmedium,eachfluidfollowsitsownflowpath.Thisflownetworkchangesfordifferentrangesofsaturationandasthenon-wettingphasesaturationreduces,thenetworkforthisphasebreaksdownandbecomesdiscontinuous;theremainingstationaryislandsofthenon-wettingphasecannotbedisplacedatpressuregradientsencounteredinhydrocarbonreservoirs.EffectsofSaturationStatesonPermeabilityThisconditionisreferredtoasresidualnon-wettingphasesaturation.Similarly,asthewettingphasesaturationdecreases,thenetworkthroughwhichthisphaseflowsbreaksdownandbecomesdiscontinuousandimmobile.Thisisreferredtoasirreduciblewetting-phasesaturation.EffectsofSaturationStatesonPermeabilityJargon(professionalvocabulary)Saturation,cementation,unconsolidatedsandsEffectsofSaturationStatesonPermeabilityDiscussions

Whatistherelationshipofwetting-phasesaturationandnon-wettingphasesaturation?Whatisirreduciblewetting-phasesaturation?Whenthewetting-phasesaturationdecreases,thenetworkbecomesdiscontinuousandstationary.Theresultofstronglywater-wetunconsolidatedsandsunfitsconsolidatedrocks,doesn’tit?ReservoirHeterogeneity

Althoughoilreservoirsarecharacterizedasporousmediawithcertainporositiesandpermeabilities,theyarealmostneverhomogeneousbedswithconstantproperties.Generally,therearenumerousstratawithwide-rangingproperties.Intermsofenhancedoilrecovery,thedivergenceofreservoirpermeabilityisasignificantfactor.Theremaybenumerousfracturesalso.Together,thepermeabilityvariationandfracturescanhaveaprofoundeffectontheflowoffluidsinareservoirandtherebyinfluenceoilrecovery.

巖心鑄體薄片X100攝像

巖心電鏡圖片X200攝像ReservoirHeterogeneityWhenwaterorotherfluidsareinjectedunderpressure,theywillseekthepathofleastresistancetothepointoflowestpressure,whichisgenerallytheproducingwell.Becausethehighpermeabilityzonesandthefracturesoffertheleastresistancetoflow,mostoftheinjectedfluidfollowsthispath.Indoingso,mostoftheoilremaininginthelowerpermeabilityzonesisbypassed.ReservoirHeterogeneityTheoilwhichisdisplacedfromthehighpermeabilityzonesandproducedisreplacedwithinjectedfluid,loweringtheresidualoilsaturationintheseregions.Astheoilsaturationdecreases,thepermeabilitytowaterincreases,furtherexaggeratingtheinequalityinrelativeflowratesbetweenthehighandlowpermeabilityzones.Theresultisever-increasingwater-tooilratiosintheproducingwellsandlowultimaterecoveryofoil-in-place(Garland,1966).ReservoirHeterogeneityVariationsofpermeabilityintheverticalplanecausetheinjectedfluidtoadvancefromtheinjectionpointasanirregularfront.Ameasureofthisvariationistheverticalsweepefficiencyorinvasionefficiency.Itisdefinedasthecross-sectionalareacontactedbytheinjectedfluiddividedbythecross-sectionalareaenclosedinalllayersbehindtheinjectedfluidfront.ReservoirHeterogeneitySimilarly,thevariationsinthehorizontalplanecauseinjectedfluidtoadvanceatanunevenrate.Thusinjectedfluidwillreachaproducingwellviatheleastresistancepathbeforesomeofthereservoirhasbeencontacted.Thearealfractionwhichhasbeencontactedatthetimeofbreakthroughofinjectedfluidisdefinedasthearealsweepefficiency.ReservoirHeterogeneityThevolumetricsweepefficiencyisameasureofthethree-dimensionaleffectofreservoirheterogeneities.Itistheproductofthepatternarealsweepandverticalsweep.Statedanotherway,thevolumetricsweepefficiencyistheporevolumeofthereservoircontactedbytheinjectedfluiddividedbythetotalporevolume(Townsendetal,1977).ReservoirHeterogeneityItshouldbenotedthattheverticalsweepefficiencyisafunctionofreservoircharacteristicsalone,whilearealsweepefficiencyisafunctionofreservoircharacteristicsandwelllocations.Thegeometricpatternforinjectionandproducingwellsaffectsthearealsweepefficiency.Improperplacementofwellscanlowerthisefficiencyevenintheabsenceofdetrimentalreservoirheterogeneities.TypesofReservoirHeterogeneitiesThegeologiststellusthatmostreservoirsarelaiddowninabodyofwaterbyalong-termprocess,spanningavarietyofdepositionalenvironments,inbothtimeandspace.Asaresultofsubsequentphysicalandchemicalreorganization,suchascompaction,solution,dolomitization,andcementation,thereservoircharacteristicsarefurtherchanged.Thustheheterogeneityofreservoirsis,forthemostpart,dependentuponthedepositionalenvironmentsandsubsequentevents,aswellasonthenatureofparticlesconstitutingthesediment.TypesofReservoirHeterogeneitiesHowever,wewould,ingeneral,expectareservoirhavesomelateralsimilarity;thatis,atanelevationcorrespondingtoagivendepositionperiod,thesamebasicparticlesizerangeshouldexistoverwidearealexpanses.Thevariationinrockpropertieswithelevationwouldbelargelyduetodifferingdepositionalenvironmentsortosegregationofdifferentlysizedorconstitutedsedimentsintolayers,ortoboth.TypesofReservoirHeterogeneitiesInasandstonereservoir,thedevelopmentofpropertiessuchasporosityandpermeabilityismostlyphysical——thatis,thepropertiesdependonthenatureofthesediment,ontheenvironmentofdeposition,andgenerallyonsubsequentcompactionandcementation.Inacarbonatereservoir,ontheotherhand,thedevelopmentofporosityismorecomplex.Inadditiontoforminginthesamemannerasitdoesinsandstones,carbonateporositymaydevelopafterconsolidationordepositionthroughselectivesolution,replacement,recrystallization,dolomitization,etc.TypesofReservoirHeterogeneitiesInbothcarbonateandsandstonereservoirs,grossrockmovementscanresultinfaultingand,evenmoreimportanttothereservoirengineer,inthedevelopmentofbothlargeandsmallreservoirfractures.TypesofReservoirHeterogeneitiesOurdiscussionofthetypesofreservoirheterogeneitieswillbedividedintothreecategories:arealvariations,verticalvariations,andreservoir-scalefractures.

TypesofReservoirHeterogeneitiesItisobviousthatthereservoirmaybenonuniforminallintensivepropertiessuchaspermeability,porosity,poresizedistribution,wettability,connatewatersaturationandcrudeproperties.GasandCondensateReservoirsItispossibletohaveafreegasaccumulationwithnooilzoneunderit.Justasinthecaseofoil,thegasmaybecontainedinaclosedreservoirwherethereisnowatercloselyassociatedwiththegasor,ontheotherhand,itmaybeinareservoirwhereitisindirectcontactwithanaquiferpossessingacompetentwaterdrivemechanism.GasandCondensateReservoirsInthefirstcase,wherethewaterdrivemechanismispoorornon-existent,thegasisdrivenoutoftheporesofthereservoirrockbytheexpansionofthegasitself,thereservoirpressurewilldecline,andtheproductionofthewellswillfall.GasandCondensateReservoirsInthesecondcase,wherethereisaneffectivewaterdrivemechanisminoperation,thegaswillbedrivenoutbytheexpansionoftheaquiferwaterintotheporesvacatedbythegas,andtherewillbenomarkeddecreaseinthereservoirpressureorintheproductioncapacitiesofthewellsduringtheirproducinglife.GasandCondensateReservoirsWhereaneffectivewaterdrivemechanismexists,thesameconsiderationsariseaswithanoilwell—thewellsshouldnotbelocatedtoonearthe“gas/watercontact”,norshouldproductionratesbesohighastocausefingeringorwaterconing.GasandCondensateReservoirsIncertaininstancesgasreservoirsofhighpressureandtemperature,whichareusuallyfoundatgreatdepthproducesubstantialquantitiesofliquidpetroleumalongwiththegas.Thisli