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SEG-2011-0504

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SEG 2011 0504
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MonitoringremainingoilbyusingpulsedneutrondualspectrumloggingtechnologyanditsapplicationZHANGFeng*,YUANChao,FANGWenJingandLIUJunTao,ChinaUniversityofPetroleumSummaryPulsedneutronloggingtechnologyhasbeenwidelyusedtodetermineremaininghydrocarbonsaturationintheoilfield.However,singlemeasurementisonlyacquiredaccordingtoformationconditionsinoneactualloggingatpresent,whichcanresultintheuncertaintyoftheinterpretationofloggingdata.Thepulsedneutrondualgammaspectrumsaturationlogging(PDSL)technologypresentedinthispapercansimultaneouslyrecordtheenergyandtimespectrumofgammaraybymeansofaspecialdesignofpulseandmeasurementtimingsequence.Withthistechnology,thehydrocarbonsaturationcanbedeterminedbyusingC/O,Σorthecross-plotofC/OandΣ,inwhichoil-water-gaslayercanbeidentifiedwithunknownporosityinformationandtheuncertaintyofloggingresultisreduced.Inaddition,byusingneutronlifetimespectrumobtainedthroughamulti-exponentialdecayinversionalgorithmaccordingtogammaraytimespectrum,oilandwaterlayercanbedirectlyidentifiedandtheeffectofboreholeiseliminated.Finally,twoexamplesarepresentedtoillustratethereliabilityofPDSLtechnology.IntroductionInthelaterperiodsofoilfielddevelopment,thewaterinjectionschemeisperformedforpressuresupportandtoenhancereservoirrecovery.Somechallengesandopportunitiesarepresentedtomonitorhydrocarbonsweepandwatercontactmovementbyusingsomesaturationlogsforthefuturedevelopment(IzuAriwodoetal.,2009).Pulsedneutronloggingtechnologyhasmainlybeenemployedtodetermineremaininghydrocarbonsaturationintheoilfield.ThepulsedneutronloggingtoolhassinglefunctionformeasuringC/OorthermalneutronlifetimeinearlystageasmentionedinZhang(2007).Atpresent,thetoolismulti-functionaltodeterminehydrocarbonsaturationwithcombinationofC/Oandthermalneutronlifetimeunderdifferentmeasuringmodel.Somepulsedneutronsaturationloggingtoolswereappliedinmonitoringremainingoil,suchasReservoirSaturationTool(RST),ReservoirMonitorTool(RMT),ReservoirPerformanceMonitor(RPM),andPulsedNeutronDecaySpectrumtool(PND-S)(Jacobsonetal.,1998;Elshahawietal.,2001andGilchristetal.,1999).However,singlemeasurement,suchasC/Oorthermalneutronlifetimeacquiredinoneloggingofthesetools,candeterminetheremainingoilsaturationonlybyusingameasuredparameter.Inaddition,theoilorgassaturationisdeterminedbycombinationofthedifferentlogs.Forexample,thehydrocarbonmonitoringingassandstonereservoirusingTDTandCHFRtechniqueswasdiscussedbyHamadaetal.(2007),butthismethodisneededtoprovidetherespectivelogandtheuncertaintyoftheloggingdatainterpretation.Thispaperreleasesanewpulsedneutrondualspectrumloggingtechnique(PDSL)withspecialtimesequencedesignofpulsedneutronemissionandmeasurement.Withthistool,gammarayenergyspectrumandgammaraytimespectrumcanbeacquiredatthesametimeinonelogging,andthenhydrocarbonsaturationcanbedeterminedbyusingC/OandformationSigma(Σ).Therefore,oil-water-gaslayercanbeidentifiedwithunknownporosityinformationandtheuncertaintyofloggingresultisreduced.Inaddition,theneutronlifetimespectrumcanbeobtainedthroughamulti-exponentiallydecayinversionalgorithmaccordingtogammaraytimespectrum.Duetothedifferenttimedecayruleofcountsinboreholeandformation,oilandwaterlayercanbedirectlyidentifiedandtheeffectofboreholeeliminated.TheoryofpulsedneutrondualspectrumsaturationloggingInordertoacquireC/OandΣatthesametimeinPDSL,aspecialtimesequenceofpulseandmeasurementisdesignedtoguaranteethecountingstatisticsoftworecordeddata,asillustratedinFigure1.Figure1:TimesequenceofpulseandmeasurementInthisdesign,450repeatednarrowperiods(G1)isincludedinprevious36msandthepulsewidthofneutronsourceis35µs,theinelasticscatteringgammaenergy©2011SEGSEGSanAntonio2011AnnualMeeting504Monitoringremainingoilbyusingpulsedneutrondualspectrumloggingtechnologyanditsapplicationspectrumismeasuredinthesecondtimegate(G2)andthecapturegammaenergyspectruminthethirdtimegate(G3).Afterthis,neutronsareemittedinthefirst100µs,and100channelsofgammatimespectrumwithchannelwidthof20µsareacquired.Inthelastperiod,thebackgroundgammarayspectrumismeasuredintherangeof38ms~40ms.Itisassumedthatthedecayofthermalneutroninboreholebenotconsidered,andthenthedecayruleofthermalneutrongeneratedineachpulseafterthecaptureofnucleiinformationmaterialcanbeexpressedinformula(1).tteNtN−=0)((1)Where,N0isthermalneutroncountatthemomentt=0afteracertaindecaywhenthepulseisover;N(t)isthecountingrateofthermalneutronatthemomentt;τisthethermalneutronlifetimeofformation.Theequationoftotalthermalneutrondecaywithtimetafternpulsesofneutronemissioncanbewrittenas:]/)(/)(/)([/)(/)(/)(2121ttttNtNtNdttdNdttdNdttdNnn+++−=+++LL(2)Therefore,thetotalcountofthermalneutronmeetstheequation(3).()/()/0+τ=dNtdtNt(3)Itcanbeconcludedthatthedecayruleofthermalneutrontimespectrumaftermulti-pulseneutronemissionwithcertaintimeintervalstillmeetsthesameruleasthesinglepulse.Thegammatimespectrumcollectedinthesecondtimerangealsoincludesthecumulativecapturegammaraycountsfromtherepeatedpulseinpreviousinelasticmodelapartfromthethermalcountgeneratedbythesinglepulseinthistimerange.InPDSL,thetheoryofdetermininghydrocarbonsaturationusingC/OorΣrespectivelyhasbeenalreadymature(Larry,etal.,2004;Solon,etal.,2006;Morris,etal.,2005)anditisunnecessarytoelaboratehere.Thus,twoelsemethodstodeterminehydrocarbonsaturation,whicharethecross-plottechnologyofC/OandΣandneutronlifetimespectrum,arediscussedindetail.Atfirst,thetheoryofdetermininghydrocarbonsaturationwiththecross-plottechnologyisdiscussed.Ifasimplemodelofpurerockformationisadopted,therelationshipofmeasuredyieldofCandO,whichisYCandYO,andformationatomicdensityinpuresandstoneformationisregardedas:COCOOOWOSn(1)n(1)n=−+−YSfff(4)Where,nCistheatomicdensityofCinoil;nOWandnOSaretheatomicdensityofOinwaterandpuresandrespectively.Accordingtotherelationshipofmacroscopiccapturecrosssectioninpurerockformation,itcanbeobtained:mahOwO(1)+(1)=−+−SSSSfSfSf(5)Then,itcanbegainedthroughequation(4)and(5):OOWmaOSWhOSWOWmaCOmaOCSnnnnnSYY])()[()()()(Σ−Σ−Σ−Σ+Σ−Σ+Σ−ΣΣ−Σ=(6)Obviously,byusingC/OandΣacquiredatthesametimeinPDSL,hydrocarbonsaturationcanbedirectlydeterminedwhenformationporosityinformationisunknown.Inaddition,thePNCisvaluableinevaluatinguntestedorunsweptreservoirsinmostlithologicalenvironments.Morris,etal.(2005)tookadvantageoftheeffectsofneutrondiffusionandimprovedtheprocessingmethodofthegammaraycountingrateresponse,whichcanprovideaccurateresultsincomplexcompletions.AsgammaraytimespectrumcanbeobtainedinPDSLtool,neutronlifetimespectrumtechniqueisemployedtodeterminehydrocarbonsaturation,inwhichtheeffectofboreholecanbeeliminatedandformationfluidsaturationdirectlydetermined.Thegammaraytimespectrumcurve,whichisgammaraycountratewithacertainerrorindifferenttimechannel,meetsthemulti-exponentialdecaylaw,andthecountrateineachchannelcanbeexpressedas:ijmjijtaNet+−=∑=)/exp(1i(7)Andthen,theneutronlifetimespectrumcanbeobtainedthroughconvertingthetimefieldintolifetimefieldwiththeaidofmulti-exponentialinversionalgorithmofgammaraytimespectrum,whichcaneliminatetheeffectofboreholeconditionandidentifyoilandwater.SimulationofdetermininghydrocarbonsaturationByusingMonteCarlomethodtobuildformationcomputationmodelincasinghole,boreholeisfilledwithfreshwater;thehydrocarbonsaturationinformationis,respectively,0,20%,40%,60%,80%,100%;thesalinityofformationwateris50g/L;thecomponentanddensityofoilis,respectively,C22H46and0.87g/cm3;theporosityofformationis,respectively,10%,15%.20%,,25%,30%,35%and40%.Theinelasticgammaenergyspectrumandgammatimespectrumatfardetectorarerecorded.Andthen,theintersectionrelationshipofC/OandformationΣisshowedinFigure2.©2011SEGSEGSanAntonio2011AnnualMeeting505Monitoringremainingoilbyusingpulsedneutrondualspectrumloggingtechnologyanditsapplication10121416180.60.70.80.91.01.11.2C/OΣ/c.u.So=0So=20%So=40%So=60%So=80%So=100%EverypointstandsforthevalueofC/OandΣunderacertainhydrocarbonsaturationandformationporosity.ThechangeofformationporositycanleadtothechangeofC/OandΣatthesametime,butthechangeisonlythepositionofthepointandthehydrocarbonsaturationisunchangedinthecross-plot,sothehydrocarbonsaturationcanbedetermineddirectlyusingC/OandΣ.Therefore,thehydrocarbonsaturationcanbedeterminedbyusingthecross-plottechnologyofC/OandΣundertheconditionofunknownporosityinformation.Figure2:Thecross-plotofC/OandΣundertheconditionofdifferentsaturationformationResultsTwoexamplesarepresentedtodemonstratetheapplicationofpulsedneutrondualgammaspectrumloggingtechnology.HydrocarbonsaturationisdeterminedbyC/Oandthecross-plotC/OandΣtechniqueinonewellfromShengliOilFieldinChinaandthemethodofneutronlifetimespectrumobtainedfrommulti-exponentiallyinversionperformedinanotherwellfromDagangOilFieldinChina.Figure3showstheprocessingandinterpretationresultofPDSLtoolforanewwelldrilledtoinspectloggingdata.Thelefttwocurvesresultsfromopenhole,thethirdchannelistheporosityindicationcurve,andthefourthchannelfortheoilindication,thefifthcurveforlithologicalindication.Inaddition,thesixthchannelisforlithologyanalysis,andtheseventhchannelforsaturationanalysisandtheeighthchannelfortheneutronlifetimelogging.Blackandbluecurvesareobtainedfromothertypesofloggingtools.ItcanbeconcludedfromthefigurethatthehydrocarbonsaturationsgainedfromotherC/OtoolsandPDSLtoolareverysimilar,butthehydrocarbonsaturationvaluemeasuredbyPDSLtoolisalittlelowerthanotherC/OtoolsinformationwithhighshalecontentastheformationSigmaiseffectedbyshalecontent.Figure3:HydrocarbonsaturationprocessingresultfromShengliOilFieldFig.4showstheneutronlifetimespectrumresultfromDagangOilFieldandtheintervalfrom3050mto3120misdiscussed.Steelcasingisadoptedinthiscompletionwell,theporosityofsandstoneformationisabout18%~23%andthesalinityofformationwateris7.091g/l.Thethirdchannelshowsthecountrateofcapturegammaray,thefourthchannelindicatesthecorrespondingformationmacroscopiccapturecrosssection(SIGMA),andthefifthchannelreflectstheneutronlifetime(τ)calculatedfromthe©2011SEGSEGSanAntonio2011AnnualMeeting506Monitoringremainingoilbyusingpulsedneutrondualspectrumloggingtechnologyanditsapplicationgammaraytimespectrumbyusingmulti-exponentialinversionalgorithmmethod.Figure4:NeutronlifetimespectrumprocessingresultfromDagangOilFieldComparedwithGRandSPcurvesinFig.4,the23rdand25thlayerbelongtothereservoirjudgedfromSPcurve,andthe28thlayerisalsoareservoirbecauseofthelowlevelGRvalue.Thesethreereservoirlayerscanbefromjudgefromchromatogram.Inthelayerwithdepthfrom3101mto3106m,thecountingrateofthermalneutronshowsslowdecaytrendwiththeincreaseoftime,whilethesectionfrom3059mto3061mandfrom3072mto3074mshowthehighestdecay.Theslowerthecountrateofthermalneutrondecays,thelargertheformationneutronlifetimeis,wherebythethreelayerscanbeestimatedasreservoirasmentionedabove.However,sinceneutroncapturecapabilityishigherinshalelayer,theneutroncountingratedecaysfasterwiththeincreaseoftimethanotherlayers,thusthesectionfrom3098mto3100mcanbejudgedasshalelayer.Accordingtothewholespectrumoftheneutronlifetimeinallwellsections,theeffectofboreholeonlifetimeiseliminatedandtheaverageneutronlifetimecanbeobtained,andsothecalculatedvaluesofhydrocarbonsaturationinthe23rd,25thand28thlayerare,respectively,32%,35%and56%.Throughthevalidationwithtestingresult,thehydrocarbonsaturationresultobtainedfromneutronlifetimespectrumisreliable.ConclusionThepulsedneutrondualgammaspectrumsaturationlogging(PDSL)technologycansimultaneouslyrecordgammarayspectroscopyandgammarayspectrumbymeansofaspecialdesignofpulseandmeasurementtimingsequence.Thecountingstatisticsofinelasticscatteringandcapturegammarayissuperiortosimilartoolsandthatofgammatimespectrumisbetterthanconventionalneutronlifetimeloggingtool.WithPDSLtechnology,hydrocarbonsaturationcanbedeterminedbyusingC/O,Σorthecross-plotofC/OandΣ,andoil-water-gaslayercanbeidentifiedundertheconditionofunknownporosityinformation,whichcanreduceuncertaintyofloggingresults.Inaddition,theneutronlifetimespectrumisobtainedthroughamulti-exponentialdecayinversionalgorithmaccordingtogammaraytimespectrum.Ithastwopeaks,oneofwhichreflectsboreholezoneandanotheronetheformation,inwhichoilandwaterlayercanbedirectlyidentifiedandtheeffectofboreholeiseliminated.Throughtheprocessingresultfrompracticalloggingdatainoilfield,theresultfromPDSLtechnologyissimilarwiththatfromotherloggingmethodsandthereliabilityofPDSLisvalidated.AcknowledgementsThanksforthesupportbytheNationalNaturalScienceFoundationofChina(40774058).©2011SEGSEGSanAntonio2011AnnualMeeting507EDITEDREFERENCESNote:Thisreferencelistisacopy-editedversionofthereferencelistsubmittedbytheauthor.Referencelistsforthe2011SEGTechnicalProgramExpandedAbstractshavebeencopyeditedsothatreferencesprovidedwiththeonlinemetadataforeachpaperwillachieveahighdegreeoflinkingtocitedsourcesthatappearontheWeb.REFERENCESElshahawi,H.,K.Gad,andA.William,2001,EnhancedC/Ologgingasaneffectivecased-holesaturationmonitoringsolution:CasehistoriesfromtheGulfofSue:SPE71743.Gilchrist,W.A,E.Prati,andR.Pemper,1999,Introductionofanewthrough-tubingmultifunctionpulsedneutroninstrument:SPE56803.Hamada,G.M.,andA.A.Hegazy,2007,HydrocarbonpotentialmonitoringingassandstonereservoirsusingTDTandCHFRtechniques:SPE105003.Khisamutdinov,A.I.,andM.A.Phedorin,2006,Numericalmethodofevaluatingelementalcontentofoil-watersaturatedformationsbasedonpulsedneutron-gammainelasticlogdata:SPE104342.Jacobson,L.,R.Ethridge,andG.Simpson,1998,Anewsmall-diameterhigh-performancereservoirmonitoringtool:SPWLA39thAnnualLoggingSymposium.Jacobson,L.A.,andT.Jerry,2004,C/Ologgingingravel-packs:SPWLA45thAnnualLoggingSymposium.Morris,C.,T.Aswad,andF.Morris,2005,Reservoirmonitoringwithpulsedneutroncapturelogs:SPE94199.Solon,T.P.,E.Escobar,andM.,Ramonez,2002,NewC/Omethodologyappliedforreservoirmonitoringinatypicalcasingcompletionandcomplexlithology:Acasestudy:SPE77788.Zhang,F.,J.P.Xu,L.M.Hu,C.H.Xiu,andJ.M.Sun,2007,MonteCarlosimulationresultforthepulsedneutron-neutronloggingmethod:ChineseJournalofGeophysics,50,no.6,1925–1931.©2011SEGSEGSanAntonio2011AnnualMeeting508
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