Production+Data+Analysis+of+Shale+Gas+Reservoirs+

SPE116688ProductionDataAnalysisofShaleGasReservoirsAdamM.Lewis*andRichardG.Hughes,LouisianaStateUniversityCopyright2008,SocietyofPetroleumEngineersThispaperwaspreparedforpresentationatthe2008SPEAnnualTechnicalConferenceandExhibitionheldinDenver,Colorado,USA,21–24September2008.ThispaperwasselectedforpresentationbyanSPEprogramcommitteefollowingreviewofinformationcontainedinanabstractsubmittedbytheauthor(s).ContentsofthepaperhavenotbeenreviewedbytheSocietyofPetroleumEngineersandaresubjecttocorrectionbytheauthor(s).ThematerialdoesnotnecessarilyreflectanypositionoftheSocietyofPetroleumEngineers,itsofficers,ormembers.Electronicreproduction,distribution,orstorageofanypartofthispaperwithoutthewrittenconsentoftheSocietyofPetroleumEngineersisprohibited.Permissiontoreproduceinprintisrestrictedtoanabstractofnotmorethan300words;illustrationsmaynotbecopied.TheabstractmustcontainconspicuousacknowledgmentofSPEcopyright.AbstractUnconventionalshalegasreservoirshavebecomeaveryimportantpartoftheresourcebasethroughouttheworld,butespeciallyintheUnitedStates.ProductiondataanalysistechniquesusingvariousformsofmaterialbalancetimeoriginallyputforthbyPalacioandBlasingame(1993)havebeenproposedandvalidatedinrecentpublicationsforavarietyofproblems(includingshalegasandcoalbedmethanesystems)usinganadjustedsystemcompressibilityfunctionsimilartothatproposedbyBumbandMcKee(1988)toaccountforadsorbedgas.Thesemodifiedmaterialbalancesolutionsallowfortypecurves(rateorpressuresolutions)tobeusedinaconventionalanalysismanner.Thesignificantchallengeintheapplicationofproductiondataanalysisforshalegassystemsistodeterminewhattheparametervalues(analysisresults)representwithinthecontextoftheinherentcomplexityofthesesystems.Inthisworkweproposeaslight(butsubstantive)modificationtomaterialbalancetimeandapplythetechniquetosyntheticandfielddatatoassessthecapabilityofthisapproachfortheanalysisofproductiondatafromgasshales.TheformulationweuseisthatofCox,etal.(2002)whichprovidesameansforevaluationproductiondataasanequivalentwelltest,whereweareabletoobservecharacteristicflowregimesinthedataandconstrainseveralofthekeyparametersofinterestsinshalegassystems.Whilethefieldresultsaredifficulttocorroborate,therelativemagnitudesoftheparametersweobtainedappeartobereasonable.IntroductionThevastmajorityofgasproductionintheUnitedStatescomesfromwhatareknownasconventionalhydrocarbonreservoirs.However,theseconventionalreservoirsarebecomingincreasinglydifficulttofindandexploit.Inaneraofrisingpricesforcrudeoilandnaturalgas,theabilitytoproducethesecommoditiesfromunconventionalreservoirsbecomesveryimportant.TheUnitedStatesGeologicalSurveystatesthat,amongotherthings,anunconventionalreservoirmusthaveregionalextent,verylargehydrocarbonreservesinplace,alowexpectedultimaterecovery,alowmatrixpermeabilityandtypicallyhasalackofatraditionaltrappingmechanism(Schenk,2002).Inparticular,shalegasreservoirspresentauniqueproblemtothepetroleumindustryinthattheymaycontainnaturalgasintheporespacesoftheverytightreservoirrock,intheporespacesofnaturalfracturesintheformationandonthesurfaceoftherockgrainsthemselveswhichisreferredtoasadsorbedgas(Montgomery,etal.,2005).Thissorbedgaspresentsdifficultiesinthatdesorptiontime,desorptionpressure,andvolumeoftheadsorbedgasallplayaroleinhowthisgasaffectstheproductionofthetotalsystem.Adsorptioncanallowforsignificantlylargerquantitiesofgastobeinplaceandpossiblyproduced.Historically,thefirstcommerciallysuccessfulgasproductionintheU.S.camefromwhatwouldnowbeconsideredanunconventionalreservoirintheAppalachianBasinin1821.Currently,someofthelargestgasfieldsinNorthAmericaareunconventional,shalegasreservoirssuchastheLewisShaleoftheSanJuanBasin,theBarnettShaleoftheFortWorthBasin,andtheAntrimShaleoftheMichiganBasin.Inaddition,gasproductionfromunconventionalreservoirsaccountsforroughly2%oftotalU.S.drygasproduction(Hill,etal.,2007).Shalegasreservoirspresentnumerouschallengestoanalysisthatconventionalreservoirssimplydonotprovide.Thefirstofthesechallengesisthedualporositynatureofthesereservoirs.Similartocarbonatereservoirs,shalegasreservoirsalmostalwayshavetwodifferentstoragevolumesforhydrocarbons,therockmatrixandthenaturalfractures(Gale,etal.,2007).Becauseoftheplasticnatureofshaleformations,thesenaturalfracturesaregenerallyisolatedorclosedduetothepressureoftheoverburdenrock(Gale,etal.,2007).Consequently,theirverylowmatrixpermeability,usuallyontheorderofhundredsofnanodarcies(nd),makesun-stimulated,conventionalproductiondifficult,ifnotimpossible.Therefore,almosteverywellinashalegasreservoirmustbehydraulicallystimulated(fractured)toachieveeconomicalproduction.These*NowwithConocoPhillips,Anchorage,AKhydraulicfracturetreatmentsarebelievedtore-activateandre-connectthenaturalfracturenetwork(Gale,etal.,2007).2SPE116688Anotherkeydifferencebetweenconventionalgasreservoirsandshalegasreservoirsistheadsorbedgas.Thenatureofthesolidsorbent,temperature,andtherateofgasdiffusionallaffecttheadsorption(Montgomery,etal.,2005).Currently,theonlymethodforaccuratelydeterminingtheadsorbedgasinaformationisth