Unconventional-shale-gas-systems-The-Mississippian

AUTHORSDanielM.Jarvie
HumbleGeochemicalServices,DivisionofHumbleInstrumentsandServicesInc.,P.O.Box789,Humble,Texas77347;[e-mail]-tionalhydrocarbonsystemsandunconventionalshale-oilandshale-gashydrocarbonsystems,includingtheBarnettShalesince1989.HeearnedaB.S.degreefromtheUniversityofNotreDameandwasmentoredingeochem-istrybyWallaceDowandDonBakerofRiceUniversity.HeispresidentofHumbleGeo-chemicalServices.RonaldJ.Hill
CentralEnergyResourcesTeam,U.S.GeologicalSurvey,Box25046,MS939,Denver,Colorado80225;[e-mail]inpetroleumgeochem-istryandhasmorethan12yearsofprofes-sionalexperience,includingthosewithExxon-MobilandChevron.Currently,heisaresearchgeologistfortheU.S.GeologicalSurvey.Hisinterestsincludeinvestigationofshale-gasre-sourcesandtheprocessesthatcontrolpetroleumgeneration.HeholdsgeologydegreesfromMichiganStateUniversity(B.S.degree)andtheUniversityofCalifornia,LosAngeles(Ph.D.),andageochemistrydegreefromtheColoradoSchoolofMines(M.S.degree).TimE.Ruble
HumbleGeochemicalSer-vices,218HigginsStreet,Humble,Texas77338;[e-mail]eochemistwithHum-bleGeochemicalServicesandiscurrentlyin-volvedinstudiesfocusedontheassessmentofshale-gasresources.HehashadadiverseprofessionalcareerthathasincludedperiodswiththeCommonwealthScientificandIndus-trialResearchOrganizationinAustralia,MobilOil,andtheU.S.GeologicalSurvey.Hehaspublishedonavarietyofgeochemicaltopics,includinglacustrinepetroleumsystems,oil-bearingfluidinclusions,nativebitumens,bio-markeranalyses,andhydrocarbongenerationkinetics.TimearnedhisB.S.degreeinchem-istryfromTrumanStateUniversityandhisM.S.degreeandhisPh.D.ingeologyfromtheUniversityofOklahoma.Unconventionalshale-gassystems:TheMississippianBarnettShaleofnorth-centralTexasasonemodelforthermogenicshale-gasassessmentDanielM.Jarvie,RonaldJ.Hill,TimE.Ruble,andRichardM.PollastroABSTRACTShale-gasresourceplayscanbedistinguishedbygastypeandsys-temcharacteristics.TheNewarkEastgasfield,locatedintheFortWorthBasin,Texas,isdefinedbythermogenicgasproductionfromlow-porosityandlow-permeabilityBarnettShale.TheBarnettShalegassystem,aself-containedsource-reservoirsystem,hasgeneratedlargeamountsofgasinthekeyproductiveareasbecauseofvariouscharacteristicsandprocesses,including(1)excellentoriginalorganicrichnessandgenerationpotential;(2)primaryandsecondarycrack-ingofkerogenandretainedoil,respectively;(3)retentionofoilforcrackingtogasbyadsorption;(4)porosityresultingfromorganicmatterdecomposition;and(5)brittlemineralogicalcomposition.Thecalculatedtotalgasinplace(GIP)basedonestimatedulti-materecoverythatisbasedonproductionprofilesandoperatores-timatesisabout204bcf/section(5.78109m3/1.73104m3).WeestimatethattheBarnettShalehasatotalgenerationpotentialofabout609bblofoilequivalent/ac-ftortheequivalentof3657mcf/ac-ft(84.0m3/m3).Assumingathicknessof350ft(107m)andonlysufficienthydrogenforpartialcrackingofretainedoiltogas,atotalgenerationpotentialof820bcf/sectionisestimated.Ofthispoten-tial,approximately60%wasexpelled,andthebalancewasretainedforsecondarycrackingofoiltogas,ifsufficientthermalmaturitywasreached.GasstoragecapacityoftheBarnettShaleattypicalreser-voirpressure,volume,andtemperatureconditionsand6%porosityshowsamaximumstoragecapacityof540mcf/ac-ftor159scf/ton.AAPGBulletin,v.91,no.4(April2007),pp.475–499475Copyright#2007.TheAmericanAssociationofPetroleumGeologists.Allrightsreserved.ManuscriptreceivedJune17,2006;provisionalacceptanceAugust24,2006;revisedmanuscriptreceivedNovember28,2006;finalacceptanceDecember19,2006.DOI:10.1306/12190606068INTRODUCTIONUnconventionalshalegashasevolvedintoanimportantresourceplayfortheUnitedStates,accountingformorethan14%ofpro-ducedgasintheUnitedStatesbytheendof2004(EnergyInforma-tionAdministration[EIA],2004).Thesearetypicallysourcerocksthatalsofunctionasreservoirrocksandareaclassofcontinuouspetroleumaccumulations(Schmoker,1995).Anunconventional,continuouspetroleumsystemconsistsofanaccumulationofhy-drocarbonsthatarefoundinlow-matrix-permeabilityrocksthatdependonfracturepermeability(eithernaturalorasaresultofstimulation)forproductionandcontainlargeamountsofhydro-carbons,butwithlowgasrecoveryfactors(Schmoker,1995).Shale-gassystemsareoftwodistincttypes:biogenicandther-mogenic(Claypool,1998),althoughtherecanalsobemixturesofthetwogastypes.Biogenicshale-gasplays,suchastheAntrimShaleoftheMichiganBasin(Martinietal.,2003),containdrygasadsorbedtoorganicmatter.Afterdewatering,thesewellswillhavemodestinitialgasflowratesinthe50–400mcf/day(1416–11,327m3/day)range,butwithproductionhistoriesupwardof30yr.Severaltypesofcontinuous,thermogenicshale-gassystemsex-ist,including(1)high-thermal-maturityshales(e.g.,BarnettShaleoftheFortWorthBasin);(2)low-thermal-maturityshales(e.g.,someNewAlbanyShaleinareasoftheIllinoisBasin);(3)mixedlithologyintraformationalsystemscontainingshale,sands,andsilts(e.g.,BossierShaleofeastTexas);(4)interformationalsystemswheregasisgeneratedinamatureshaleandstor