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SPE-59369-MS

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SPE 59369 MS
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Copyright2000,SocietyofPetroleumEngineersInc.Thispaperwaspreparedforpresentationatthe2000SPE/DOEImprovedOilRecoverySymposiumheldinTulsa,Oklahoma,3–5April2000.ThispaperwasselectedforpresentationbyanSPEProgramCommitteefollowingreviewofinformationcontainedinanabstractsubmittedbytheauthor(s).Contentsofthepaper,aspresented,havenotbeenreviewedbytheSocietyofPetroleumEngineersandaresubjecttocorrectionbytheauthor(s).Thematerial,aspresented,doesnotnecessarilyreflectanypositionoftheSocietyofPetroleumEngineers,itsofficers,ormembers.PaperspresentedatSPEmeetingsaresubjecttopublicationreviewbyEditorialCommitteesoftheSocietyofPetroleumEngineers.Electronicreproduction,distribution,orstorageofanypartofthispaperforcommercialpurposeswithoutthewrittenconsentoftheSocietyofPetroleumEngineersisprohibited.Permissiontoreproduceinprintisrestrictedtoanabstractofnotmorethan300words;illustrationsmaynotbecopied.Theabstractmustcontainconspicuousacknowledgmentofwhereandbywhomthepaperwaspresented.WriteLibrarian,SPE,P.O.Box833836,Richardson,TX75083-3836,U.S.A.,fax01-972-952-9435.AbstractThispaperpresentsthefirstresultsofanongoingexperimentalworkatIFEfordevelopingnewtracerstobeusedforestimationofremainingoilsaturation.Themethodologyisbasedonthechromatographictheory,whichstatesthatvariouscomponentsflowingthroughporousmediawillbedelayedaccordingtotheirpartitioncoefficienttotheimmobilephase.Twoexperiments,onewithgastracersandtheotherwithwatertracers,arepresentedhere,demonstratingtheapplicabilityofthemethodologyinthelaboratoryscale.Moreover,anumericalmodel(ITRC-SIMmodule)developedatIFEespeciallyforsimulatingthetracerflowinhydrocarbonreservoirsisvalidatedagainsttheexperimentaldataandusedtodemonstratetheuseoftracersinsmallandfieldscalegenericcases.IntroductionTracersareinertchemicalcompoundswidelyusedtoimprovethedescriptionofhydrocarbonandwaterreservoirs.Watertracersaredividedintotwocategories:theideal(orpassive)tracers,whichalwaysfollowtheaqueousphase,andthepartitioningtracers,whichpartitionbetweentheaqueousandtheoilphase.Idealtracersareusedmainlyininterwelltracertestsinordertoobtaininformationabouttheflowpatternsandtoestablishthevelocityfieldandthewellcontinuity.Thetracerdatacanalsobeusedtoupgradeareservoirmodel(1).Partitioningtracers,whicharethesubjectofthispaper,areusedinhydrocarbonreservoirsinbothsinglewelltracertestsandinter-welltracerteststoestimatetheresidualoilsaturationusuallypriortoenhancedoilrecoveryapplications(2).Thegastracersarealwayspartitioningbetweentheoilandgasphases.Themostcommonlyappliedwatertracersaretritiatedwater(HTO),thiocyanadeandsomemonofluorobenzoicacids.Themostcommonlyusedgastracersaretritiatedmethane,SF6andseveralperfluorocarbonswithlowpartitioningtooilphase.Inthispaper,thefirstresultsofanexperimentalevaluationofnewgasandwaterpartitioningtracersfortheestimationofremainingoilsaturationinhydrocarbonreservoirsarepresented.Anumericalmodel,(ITRC-SIM)builtwithadvancedphysicalandnumericalfeatures,hasbeendevelopedandvalidatedagainsttheexperimentaldata.Finally,theapplicationofpartitioningtracersinoilreservoirsisdiscussedinsmallandfieldscalegenericcases.PartitioningTracersforEstimationofResidualOilSaturationWhenidealandpartitioningwatertracersareinjectedsimultaneouslyinanoilreservoir,theidealtracerswillflowonlyinthewaterphaseadoptingthevelocityofthisphase.Ontheotherhand,themoleculesofthepartitioningtracersaremovingbackandforthbetweenthewaterandoilphase.Consequentlythepartitioningtracermoleculesareflowingwiththewatervelocitywhentheyareinthewaterphaseandtheoilvelocitywhentheyareintheoilphase.Asaresultofthischromatographiceffectthereisanettimedelayonthearrivalofthepartitioningtracersattheproductionwellcomparedwiththearrivaltimeoftheidealtracers.Thistimedelaydependsonthepartitioningcoefficients(whichcanbemeasuredinthelaboratory)andtheoilsaturation.Thesamemethodologycanbeappliedinagas-oilsystemwiththeuseoftwogastracerswithdifferentpartitioningcoefficients.Deans(3)showedthatthefollowinggeneralrelationshipcanbeusedfortheestimationoftheresidualoilsaturationwhentheoilfractionalflowisnegligible:1211RKKRRSor−+−−=(1)where:12ttR∆∆=SPE59369ApplicationofPartitioningTracersforRemainingOilSaturationEstimation:AnExperimentalandNumericalStudyC.Chatzichristos,SPE,Ø.Dugstad,SPE,A.Haugan,J.Sagen,J.Muller,IFE2C.CHATZICHRISTOS,Ø.DUGSTAD,A.HAUGAN,J.SAGEN,J.MULLERSPE59369∆t1,∆t2:thetimethatisrequiredforthetracerstotravelfromtheinjectionwelltotheproductionwell.K1,K2:theK-valuesofthetwotracers,definedastheratiooftheconcentrationoftheimmobilephaseovertheconcentrationofthemobilephase.Forthecaseofanidealtracerandapartitioningtracer(K)eq.(1)reducesto:KttttSor+∆∆=00(2)where0tisthebreakthroughtimeoftheidealtracerandt∆isthetimedelayonthearrivalbetweenthepartitioningandtheidealtracer.Severalmethodshavebeenproposedforthedeterminationofthebreakthroughtimeofthetracers.Inreservoirapplications,the“peakmethod”isthemostreliablebecauseitisnotinfluencedbythephysicaldispersion.Inthismethod,thetimecorrespondingtothemaximumconcentrationofthetracerresponsecurveisconsideredtobethebreakthroughtime.Itshouldbementionedthatatracerresponsecurvemighthaveseveralpeaks,eachofthemcorrespondingtoadifferentflowpath.ExperimentalEvaluationofGasandWaterPartitioningTracersTheobjectiveoftheexperimentsistofindnewgasandwatertracersthatcanbeappliedforestimationofresidualoilsaturationinwell-to-wellstudies.GasTracersExperimentalprocedure.Dynamictestingofperfluorocarbon(PFC)gastracerswascarriedoutinaslimtubeof6m,whichwaspackedwithcrushedOttawasand.Theexperimentalset-upisillustratedinFig.1.Initiallytheslimtubewasfilledwithdeadoil.Theoilwasdisplacedbygas,at150bar,untilresidualoilsaturationwasobtained.Thetemperaturewas100oC.Duringthewholeexperimenttheflowrateoftheinjectiongaswas0.037ml/min.Thetotalporevolumeintheslimtubewas38.5ml.Theresidualoilsaturationwasmeasuredto0,27byusingtheweighingmethod.ThedensitiesofthetwophasesattheexperimentalconditionswerecalculatedusingCMGsPVTsimulator.TheexperimentwascarriedoutusingoilfromtheEkofiskfieldinNorthSea,andsyntheticgaswiththefollowingcomposition:84%C1,9%C2,6%C3and1%nC4.Whenonephase(gas),steadystateflowhasbeenestablished,thetracerpulseisinjected.Thetracerstestedinthisexperimentare:perfluoro-methyl-cyclohexane(PMCH),1,2-perfluoro-dimethyl-cyclohexane(1,2-PDMCH),1,3-perfluoro-dimethyl-cyclohexane(1,3-PDMCH),cis-perfluoro-decaline(c-PFD),trans-perfluoro-decaline(t-PFD)andperfluoro-1-methyl-decaline(PF1mD).ThetracerswereautomaticallyanalysedintheeffluentgasusingaGC/ECD(4).TheK-valuesofthetracersweremeasuredunderstaticconditionsandarepresentedinTable1.Results.TheconcentrationresponsesofthetracersintheeffluentareillustratedinFig.2.Table2showsthetracertransittimemeasuredduringtheexperiment.InadditiontheK-valuesfortheindividualtracersandtheresidualoilsaturationcalculatedfromEquation1arepresented.Thetracertransittimeisbasedonafirstmomentcalculationofthetracerresponse.TheoilsaturationisestimatedusingbothPMCHand1,3-PDMCHasprimarytracer.Itcanbeseenthatthereisafairagreementbetweentheestimationoftheoilsaturationusingthegastracersandtheweighingmethod.Water/OilPartitioningTracersFivefluorinatedbenzoicacidtracershavebeentestedinaflowexperimentonanoilsaturatedFelsersandstonecore.ThedifferentfluorinatedacidsarelistedinTable3,togetherwiththeabbreviationsusedinthisreport.ThemaingoalwastocompareK-values,previouslymeasuredinacrudeoil/seawaterbatchsystem,withtheK-valuesobtainedinachromatographicsystematsimulatedreservoirconditions.Experimentalprocedure.,Theexperimentwascarriedoutusinga“highpressure”corecellwithlowdeadvolume.Thetemperatureandpressureconditionswere90oCand200bars.TheexperimentalequipmentisshowninFig.3.Thecorewaspreparedtocontainresidualoilsaturationusingthestandardprocedurebyalternatingflowofseawaterandcrudeoil.Theporevolumeinthecorewas,priortooilsaturation,determinedbyHe-porosimetry.ThegeneralexperimentalconditionsanddataaregiveninTable4.Whenresidualoilsaturationhadbeenestablished,thecorewasfloodedwithsyntheticseawaterattheconstantflowrateof0.01ml/min.Duringthisperiodasmallvolumeoftracerswasinjectedinone“pulse”intotheflowingwaterphaseclosetothecoreinlet.HTOwasincludedasareferencetracerinthetracerpulse.Thewaterfloodingcontinuedatstableflowrateuntilthetracerchemicalswereelutedthroughthecoreplug.Aliquotsof0.1mloftheeffluentwerecontinuouslycollectedbyasamplefractioncollectorclosetotheoutletofthebackpressureregulatorvalve.ThesamplefractionswereanalysedforitscontentoffluorinatedbenzoicacidtracersbyHPLCtechniquesandtheHTOactivitybyliquidscintillationcounting.ThecompositionofthetracersolutionisgiveninTable5,andthesyntheticseawatercompositioninTable6.Results.ThetracerpulseresponsecurvesfromtheFelsercoretestisgiveninFig.4.Itisremarkabletofindthatthe2,6-TFMBAisclearlyelutedinadvanceofthetritiatedwater.Alsothe2,4-TFMBAisinthefrontofHTO,butlesspronounced.AnexplanationforthiseffectmaybethedifferenceinthemolecularsizeofTFMBAcomparedtothewatermolecule,whichcanleadtohindrancefortheTFMBAtopenetrateintothesmallerpores.Asthe2,6-TFMBA,withthesubstitutedfluorinatedmethylgroupclosetotheacidgroupisexpectedtoSPE59369APPLICATIONOFPARTITIONINGTRACERFORREMAININGOILSATURATIONESTIMATION:3ANEXPERIMENTALANDNUMERICALSTUDYbemoredissociatedthanthe2,4-TFMBA,itseemsthattheeffectismagnifiedbytheionicstrengthofthemolecule.The2,6-TFMBAmaycreatestrongeranionrepulsionfromtheporewallthanthe2,4-TFMBA,anditiswellknownthatfluidvelocitiesarehighestattheporecentre.Thepartitioningcoefficientshavebeencalculatedonthebasisofchromatographictheory.Inthepresentcalculations,withtheresultsgiveninTable7,thecurvesweresmoothenedbyaveragingfiveadjacentconcentrationvaluesalongthegraph.Themaximumconcentration,ortoppointofthecurves,wasusedtodefinetheretentiontimeintheK-valuecalculations.TheK-valuesobtainedfromthemeasurementswiththeFelsercoreareinrelativegoodagreementwiththeK-valuesmeasuredatphaseequilibriumconditioninstaticbatchexperiments.SimulationofTracerFlowTracertechnologyplaysanimportantroleinimprovingthereservoircharacterizationbeforetheapplicationofEnhancedOilRecoverymethodsbyprovidingqualitativeinformationonreservoircompartmentalization,flowpaths,stratification,heterogeneitiesdistributionandremainingoilsaturation.Accuratetracermodelingcanbeemployedtoquantifythisinformationandupgradeagivenreservoirmodelwithrespecttotheabovefeatures.However,inordertobeabletoresolvetheinfluenceofreservoirheterogeneitiesonthemeasuredtracerresponses,anaccuratenumericaltreatmentofthetracerequationsisrequired.Thisisespeciallyimportantwhennarrowtracerslugsareinjectedinareservoir.IFEhasdevelopedanumericalmodel(ITRC-SIM)forthispurpose,whichiscoupledtoCMG-STARSthermal/chemicalreservoirsimulator.Theinnovativefeaturesofthismodelare:1.Improvedphysicaldescription,byincluding-partitioningtracers-adsorbingtracers-fulltensordispersioncalculationandmoleculardiffusion2.Reducednumericaldispersion,byincluding-2ndordernumericalscheme-explicitintegrationofthetracerequationwithoptimizedtimestepcontrol-separategridrefinementforthetracerequationAdetaileddescriptionofthenumericalmodelcanbefoundinSagenetal.(5)SimulationoftheTracerExperimentsGastracers.Theobjectiveofthissimulationistomodelthetracerflow.Therefore,asinitialconditions,theoilphaseissetatresidualsaturationlevel.ThecomponentscomprisingthegasphasearelumpedintoonegascomponentandthecomponentscomprisingtheEkofiskoilarelumpedintooneoilcomponent.ThepropertiesofthetwocomponentsascalculatedusingtheCMG-WinproppackagearepresentedinTable8.Theslim-tubeisdividedinto60grid-blocks.Oneinjectorandoneproducerwellisconsideredinthefirstandthelastgrid-blockrespectively.Theresidualoilsaturationissetat0.27,equaltotheonemeasuredatthelaboratory.Thedimensionsoftheslim-tubeandtheotherpropertiessuchaspressure,temperatureandflowratearesetequaltotheexperimentalones.Fig.5illustratesthesimulatedtracerresponsesincomparisonwiththeexperimentalones.Itcanbeseenthatthereisaverygoodagreementbetweenthesimulatedandtheexperimentalresults,whichindicatesthatthesimulatormodelsaccuratelythetracerflow.Forsimplicity,onlythreetracersareconsideredinthissimulationselectedforthedifferencebetweentheirpartitioningcoefficients.Waterpartitioningtracers.Thesamemethodologyusedforthesimulationofgastracersisappliedalsoforthesimulationofthewaterpartitioningtracers.Alltheparametersaresetequaltotheexperimentalones.Forsimplicity,onlythreetracersareconsideredandthebatchmeasurementsofthepartitioningcoefficientsareusedforthesimulation.Fig.6showsthecomparisonoftheexperimentalwiththesimulatedresultsanditcanbeseenthatthereisaverygoodagreement.ApplicationofPartitioningTracersinGenericCasesTherearetwoimportantissuesforafieldapplicationofpartitioningtracersforestimationofresidualoilsaturation.Firstistheselectionofthepropertracerssothatthetimedifferenceonthearrivalofthetracersisadequateandcanbemeasuredforagivensamplingfrequency.Toomuchdelayofthepartitioningtracersisundesirablebecauseitwilldelaytheevaluationofthetracerperformanceandwillspreadtracerproductionoveralargetimewindow,increasingthecostsofsamplingandsampleanalysis.Furthermore,suchtimedelaywillreducethetracerconcentrationwiththedangertobebelowthedetectionlimit.Thesecondissueistheanalysisofthetracerresponsesandthedeterminationoftheoilsaturationdistribution.Theparametersaffectingthearrivaltimedelayofapartitioningtracerrelativetoanidealtracer,accordingtoequation(2),aretheoilsaturation,thepartitioningcoefficientandthetransittimeoftheidealtracer.Theoilsaturationisapropertythatobviouslycannotbeinfluenced.Thepartitioningcoefficientisanintrinsicpropertyofthetracersdependentonpressure,watersalinity,fluidcomposition,temperature,etc.Itisuptotheusertoselecttheappropriatetracersforthespecificreservoirconditions.TheeffectofthepartitioningcoefficientsonthetracerresponseisdemonstratedinFig.7.Fourtracerswithpartitioningcoefficientsof0.0(idealtracer),1.0,1.5and2.0areinjectedsimultaneouslyinaone-layerreservoir.Itcanbeseenthatasthepartitioningcoefficientincreases,thetimedifferenceonthearrivalbetweentheidealtracerandthepartitioningtracersincreases.Thetransittimeoftheidealtracerdependsontheflowrateofthemobilefluids.TheeffectoftheflowrateonthearrivaltimedelayofthepartitioningtracersispresentedinFig.8.A4C.CHATZICHRISTOS,Ø.DUGSTAD,A.HAUGAN,J.SAGEN,J.MULLERSPE59369pairofanidealandapartitioningwatertracers(K=1.0)areinjectedwiththreedifferentflowrates(100,200and500m3/day)inanone-layerreservoir.Itcanbeobservedthatastheflowrateincreasesthedelayonthearrivalofthetwotracersisdecreasing.Iftheflowratebecomesveryhigh,thenthedelaywillbecomeverysmall.Thisisimportantindesigningfieldtracerjobswhereitisdesiredthatthetimedelayissignificantenoughtobepracticallydetected.Howeverinafieldapplication,itcanbehardlyexpectedthattheflowratewillbeadjustedtosatisfythetracerperformance.Thereforethesamplingfrequencyhastobeadjustedtothetracervelocity,whichmayvaryduringthetimewindowthatthetracerisproduced.Reservoirsimulationscouldbeusedtogivepredictionsofthetracerflowandthesamplingprogramtobedesignedaccordingly.Inacaseofahomogeneousreservoirtheproblemisnotverycomplexandtheselectionofatracerwiththepartitioningcoefficientcanprovesufficienttogivethedesiredtimedelay.However,th
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