SPE167183MSP

SPE167183FractureCellforFlowModelingA.Sakhaee-Pour,andMaryF.Wheeler,UniversityofTexasatAustinCopyright2013,SocietyofPetroleumEngineersThispaperwaspreparedforpresentationattheSPEUnconventionalResourcesConference-CanadaheldinCalgary,Alberta,Canada,5–7November2013.ThispaperwasselectedforpresentationbyanSPEprogramcommitteefollowingreviewofinformationcontainedinanabstractsubmittedbytheauthor(s).ContentsofthepaperhavenotbeenreviewedbytheSocietyofPetroleumEngineersandaresubjecttocorrectionbytheauthor(s).ThematerialdoesnotnecessarilyreflectanypositionoftheSocietyofPetroleumEngineers,itsofficers,ormembers.Electronicreproduction,distribution,orstorageofanypartofthispaperwithoutthewrittenconsentoftheSocietyofPetroleumEngineersisprohibited.Permissiontoreproduceinprintisrestrictedtoanabstractofnotmorethan300words;illustrationsmaynotbecopied.TheabstractmustcontainconspicuousacknowledgmentofSPEcopyright.AbstractHydrocarbonproductionfromunconventionalresourcessuchasshaleusuallyentailsstimulationbyhydraulicfracturing,whichresultsinnon-planar(curved)fractures.However,mostreservoirmodelsassumethattheinducedfracturesareplanarforthesakeofsimplicity.Consideringthegrowinginterestofthepetroleumindustryinbetterunderstandingproductionfromtheseresources,wedevelopafracturecellmodeltocapturetheeffectsoffracturenon-planarityontransportproperties.Tobuildarealisticreservoirmodelforafracturedformation,threetypesofinteractionsmustbeaccountedfor:matrix-matrix(M-M),matrix-fracture(M-F),andfracture-fracture(F-F).Thetransportpropertiesofthematrix-matrixinteraction(M-M)arebasedonlabmeasurements.Inthisstudy,weanalyticallydeterminethetransportpropertiesofthetwoothertypesofinteractions(M-FandF-F).Forthispurpose,weaccountfortheaperturesizeandspatiallocationofthefracture.Asaresult,weprovideeffectiveporosityandeffectiveanisotropicpermeabilitiesforareservoircellthatcontainsafractureinsideit.Thereservoircellwhosetransportpropertiesaremodifiedisafracturecell.Weimplementthefracturecellmodelinareservoirsimulatorandperformanalysesforasinglefractureandformultipleintersectingfractures;thesefracturesarenon-planar.Theanalysesincludebothsingle-andmultiphaseflowmodelsandshowthatthehydrocarbonpressureinsidethereservoirisstronglydependentonthefracturegeometrywhenthematrixpermeabilityissmallerthan1microD.Thus,itiscrucialtomodelthefracturegeometrymoreaccuratelyinunconventionalreservoirswithultra-lowpermeabilitiessuchasshale.Thedevelopedfracturecellmodelcaneasilybeimplementedinreservoirsimulators,andthereisnoneedforlocalrefinementaroundthefracture.Themainadvantageoftheproposedmodelisitssimplicity,conjoinedwithitsabilitytocapturethenon-planarityofthefracture.Thedevelopedmodelhasmajorapplicationsforunderstandingproductionfromformationsthatareheavilyfractured.IntroductionProductionfromunconventionalreservoirs,especiallyshale,isofgreatinterestbecauseofthesignificanthydrocarbonvolumestoredintheseresources(Polczer2009).Itisnotclear;however,howmuchofthestoredvolumeisproducible(Urbina2011).Obtainingabetterestimationoftheproduciblefractionentailsunderstandingthetransportpropertiesoftheunconventionalresources,whichareoftenheavilyfracturedtoproduceataneconomicrate.Thetransportpropertiesofahydraulicallyfracturedshalebelongtothreegroups:thematrixofthereservoir,thefracture,andtheinteractionofthematrixandthefracture.Theflowpropertiesofeachcategoryaresubjectsofactiveresearchasweattempttoexploittheseresourcesmoreappropriately.Webeginwiththetransportpropertiesofthematrix.Manypetrophysicalparametersoftheshalearenotwellunderstood,mostlybecauseoftheextremelynarrowsizeoftheporesandtheadsorbedlayerofgasinorganic-richregions.Becauseofthenarrowsizeofthepores,wemustusehigh-Knflowmodelsinsteadofcontinuummodelstodeterminepermeability(Royetal.2007;Swamietal.2012).Theexistenceoftheadsorbedlayeralsoaddstothecomplexityoftheproblem.Thethicknessoftheadsorbedlayerlessensasthereservoirpressuredecreases,andthisleadstoanincreaseofthevoidspace.Toaccountforthiseffect,researchershavemodeledtheincreaseofthevoidspaceandhaveproposednewmodelsforporosity(Hartmenetal.2011;Ambroseetal.2012)andpermeability(Sakhaee-PourandBryant2012;Sinhaetal.2013).Theformationpermeabilitymayalsoincreaseduetoactivationoffaultswhenwecarryouthydraulicfracturestimulation.Micro-seismiceventstakingplacefarfromthefracturetipcorroboratethisnotion(Pennyetal.2006;Danielsetal.,2007).Thepermeabilityenhancementismoreprobablewhentheclaycontentoftheformationislow(Zobacketal.2012).Despitetheexistenceofthesupportingevidence,itremainsdifficulttodeterminefaultslippagefromfielddataanditseffecton2SPE167183transportproperties.Yetanotherchallengeischaracterizingflowthroughthefracturethatcontributestotransportproperties.Fracturesaremostoftencreatedoractivatedduringstimulationinshaleformations.Thestimulationismoresuccessfulwhentheinducedfracturesformacomplexnetworkastheincreaseinthecontactareismoresignificant(Fisheretal.2005).Althoughthesefracturesarenotnecessarilyplanar,mostreservoirmodelssupposethattheyareplanarforthesakeofsimplicity.Theinteractionbetween