Effects of smectite on the oil-expulsion efficienc

Effectsofsmectiteontheoil-expulsionefficiencyoftheKreyenhagenShale,SanJoaquinBasin,California,basedonhydrous-pyrolysisexperimentsMichaelD.Lewan,MichaelP.Dolan,andJohnB.CurtisABSTRACTTheamountofoilthatmaturingsourcerocksexpelisexpressedastheirexpulsionefficiency,whichisusuallystatedinmilligramsofexpelledoilpergramoforiginaltotalorganiccarbon(TOCo).Oil-expulsionefficiencycanbedeterminedbyheatingthermallyimmaturesourcerocksinthepresenceofliquidwater(i.e.,hydrouspyrolysis)attemperaturesbetween350°Cand365°Cfor72hr.Thispyrolysismethodgeneratesoilthatiscomposition-allysimilartonaturalcrudeoilandexpelsitbyprocessesopera-tiveinthesubsurface.Consequently,hydrouspyrolysisprovidesameanstodetermineoil-expulsionefficienciesandtherockprop-ertiesthatinfluencethem.Smectiteinsourcerockshaspreviouslybeenconsideredtopromoteoilgenerationandexpulsionandisthefocusofthishydrous-pyrolysisstudyinvolvingarepresenta-tivesampleofsmectite-richsourcerockfromtheEoceneKreyenhagenShaleintheSanJoaquinBasinofCalifornia.Smectiteisthemajorclaymineral(31wt.%)inthisthermallyimmaturesample,whichcontains9.4wt.%totalorganiccarbon(TOC)comprisedoftypeIIkerogen.Comparedtootherimmaturesourcerocksthatlacksmectiteastheirmajorclaymineral,theexpulsionefficiencyoftheKreyenhagenShalewassignificantlylower.TheexpulsionefficiencyoftheKreyenhagenwholerockwasreduced88%comparedtothatofitsisolatedkerogen.Thissignificantreductionisattributedtobitumenimpregnatingthesmectiteinterlayersinadditiontotherockmatrix.WithintheCopyright©2014.TheAmericanAssociationofPetroleumGeologists.Allrightsreserved.ManuscriptreceivedApril11,2013;provisionalacceptanceMay31,2013;revisedmanuscriptreceivedAugust09,2013;finalacceptanceOctober09,2013.DOI:10.1306/10091313059AUTHORSMichaelD.Lewan∼U.S.GeologicalSurvey,DenverFederalCenter,Box25046,MS977,Denver,Colorado80225;[e-mail]esearchgeochemistandgeologistfortheEnergyResourcesProgramoftheU.S.GeologicalSurveyinDenversince1991.Priorexperienceincludes13yearsasaresearchgeochemistatAmocoProductionCompanyResearchCenterinTulsa,Oklahoma,andthreeyearsasanexplorationgeologistforShellOilCompanyinNewOrleans.HehasaB.S.degreefromNorthernIllinoisUniversity,DeKalb,Illinois,anM.S.degreefromMichiganTechnologicalUniversity,Houghton,Michigan,andaPh.D.fromtheUniversityofCincinnati,Cincinnati,Ohio.MichaelP.Dolan∼DolanIntegrationGroup,252055thStreet,Suite101,Boulder,Colorado80301;[e-mail]andpresidentofDolanIntegrationGroup(DIG)andisanAAPGCertifiedPetroleumGeologist.Hespecializesintheapplicationoforganicgeochemistrytopetroleumindustryissuesandhas17yearsofoilandgasexperiencewiththeU.S.GeologicalSurvey,Mobil,ExxonMobil,andDIG.HehasaB.S.degreefromtheUniversityofIllinoisatChicago,Illinois,andanM.S.degreefromtheColoradoSchoolofMines,Golden,Colorado.JohnB.Curtis∼DepartmentofGeologyandGeologicalEngineering,ColoradoSchoolofMines,Golden,Colorado80401;[e-mail]emeritusanddirectorofPotentialGasAgencyattheColoradoSchoolofMines,Golden,Colorado.Hispriorexperienceof15yearsincludedTexaco,Columbia,Gas,andBrownandRuthLaboratories.HewascochairoftheAAPGCommitteeonUnconventionalPetroleumSystems(1999–2004),isaninvitedmemberoftheAAPGCommitteeonResourceEvaluation,andAssociatedEditoroftheAAPGBulletin(1998–2010).HehasAAPGBulletin,v.98,no.6(June2014),pp.1091–11091091interlayers,muchofthebitumenisconvertedtopyrobitumenthroughcrosslinkinginsteadofoilthroughthermalcracking.Asaresult,smectitedoesnotpromoteoilgenerationbutinhibitsit.Bitumenimpregnationoftherockmatrixandsmectiteinter-layersresultsintherockporesystemchangingfromwaterwettobitumenwet.Thischangepreventspotassiumion(K+)transferanddissolutionandprecipitationreactionsneededfortheconver-sionofsmectitetoillite.Asaresult,illitizationonlyreaches35%to40%at310°Cfor72hrandremainsunchangedto365°Cfor72hr.Bitumengenerationbeforeorduringearlyillitizationintheseexperimentsemphasizestheimportanceofknowingwhenandtowhatdegreeillitizationoccursinnaturalmaturationofasmectite-richsourcerocktodetermineitsexpulsionefficiency.CompleteillitizationpriortobitumengenerationiscommonforPaleozoicsourcerocks(e.g.,WoodfordShaleandRetortPhosphaticShaleMemberofthePhosphoriaFormation),andexpulsionefficienciescanbedeterminedonimmaturesamplesbyhydrouspyrolysis.Conversely,smectiteismorecommoninCenozoicsourcerocksliketheKreyenhagenShale,andexpulsionefficienciesdeterminedbyhydrouspyrolysisneedtobemadeonsamplesthatreflectthelevelofillitizationatornearbitumengen-erationinthesubsurface.INTRODUCTIONTheinteractionofmineralsandorganicmatterinsourcerocksduringpetroleumformationhaslongbeenofinterest(Grim,1947;Brooks,1948).Clayminerals,inparticular,wereconsid-eredtohavecatalyticeffectsthatenhancethethermaldecomposi-tionoforganicmatter(Johns,1979;Goldstein,1983).Althoughclayminerals,especiallysmectite,havecatalyticpropertiesthatcaninfluencepetroleumproducts(Clementz,1976;CzarneckaandGillott,1980;Pinnavaia,1983),experimentalpyrolysisstud-ieshaveshownsmectitetoreducepyrolyzateyieldsoralterpyrol-yz