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FinalReportofRPSEAProject12122-91:4DIntegratedStudyUsingGeology,Geophysics,ReservoirModeling&RockMechanicstoDevelopAssessmentModelsforPotentialIn-

ducedSeismicityRisk

PrincipalInvestigator:JeremyBoak,OklahomaGeologicalSurvey,UniversityofOklahomaInvestigators: G.R.Keller,ret.,OklahomaGeologicalSurvey,UniversityofOklahoma

AustinHolland,UnitedStatesGeologicalSurvey,UniversityofOklahomaJeffersonChang,OklahomaGeologicalSurvey,UniversityofOklahomaStephenHolloway,OklahomaGeologicalSurvey,UniversityofOklahomaChenChen,OklahomaGeologicalSurvey,UniversityofOklahomaNoorulanGhouse,OklahomaGeologicalSurvey,UniversityofOklahomaFernandoFerrerVargas,OklahomaGeologicalSurvey,UniversityofOklahoma

AndrewThiel,OklahomaGeologicalSurvey,UniversityofOklahomaStevenMarsh,OklahomaGeologicalSurvey,UniversityofOklahomaDeepakDevegowda,MewbourneSchool,UniversityofOklahomaAhmadGhassemi,MewbourneSchool,UniversityofOklahoma

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TableofContents

ExecutiveSummary ES-1

1. PatternsofInducedSeismicityinCentralandNorthwestOklahoma 1

2. OklahomaEarthquakeSummaryReport2015-16 8

3. GravityDataCollection 22

4. SeismicTomographyofNorthCentralOklahoma 27

5. GravimetricDeterminationofBasementGeologicStructure 41

6. InterpretationofLowFrequencyPressureMeasurementsinInjectionandProductionWells 57

7. ModelingPorePressureVariationsandPotentialforInducedSeismicityAdjacenttoWaterDis-posalWells 67

8. IntegratedRockMechanicsStudies 85

9. TechnologyTransferActivities 95

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ExecutiveSummary

ThegoalofthisProjectwastoevaluatewhatpropertiesmaybemosthelpfulinrigorouslyidentifyingbothinducedseismicityandthepotentialforinducedseismicity,basedonmod-elingandphysicalmeasurementsinthetargetareainCentralOklahoma.ThestudyareaislocatedinthezoneofincreasedseismicityofcentralOklahomatoaddressscientificquestionswithrespecttothegeologicconditions,monitoringandpredictivemodelingnecessarytoevaluatepotentialcausesoftheincreasedseismicity.Theteambuilt,testedandupdatedavolumetric(3D)geologicinterpretation,basedoninformationfromexistingwellandwell-logdatabases,rock-mechanics,rockproperties,andseismicimaging.The3Dgeologicinterpretationwastestedagainstexistingandnewlyacquiredgravitydata,aswellasongoingseismicmonitoringwithinthestudyarea.Theongoingseismicityaddedtothe3Dvelocitystructurewithinthe3Dgeologicinterpretationvolume.Atthesametime,thegravitymodelingaddedtothe3Ddensitydistributionwithinthesameinterpretationvolume.Usingthegeologicinterpretationalongwithproductionandwaterdisposalinformation,reservoirandrockmechanicsmodelingwereundertakentoexaminethechangesthroughtimeassociatedwithoilandgasproductionaddingadditionalinformationdimensions(4D)tothestudy.Thisreportisdividedintoeightchaptersdescribingresultsfortechnicalaspectsofthepro-jectandalistingofTechnologyTransferactivitiesduringthetermoftheproject.EachChapterisprecededbytheRPSEATaskdescriptionforthetask(exceptChapter1,whichisanintroductiontotheevolutionofseismicactivitythatisthesubjectofthisproject).Aseparatepackage,comprisingtwoOpenFileReports,presentstheresultsofcompilationoffaultdatafromliteratureandoilandgascompanyfilesthatwasfundedinpartbythisproject.Chapter1isadiscussionofthetrendsinseismicityandtheregulatoryresponsetothatac-tivity.Itpointsoutthesignificantincreaseinearthquakefrequencyduringthefirstyearoftheproject,andtheflatteninganddeclineofthefrequencysincemid-2015.BothtrendsreflectthevariationofinjectionvolumesintheArbuckleGroupsedimentaryrocksthatisconsideredthecriticaldriverofseismicity.ItalsopointsoutthesignificanceofthedecreaseinoilpriceandtheactionsoftheOklahomaCorporationCommissioninregardtothosechanges.Oklahomaexperiencedanaverageof1.6earthquakesofMagnitude3orgreater(M3.0+)fromthe1980sthrough2008.Sincethattime,seismicityhasincreasedto903M3.0+earthquakesin2015.Earthquakefrequencyhasdeclinedin2016;however,Oklahomaex-perienceditslargestearthquake,aM5.8eventinSeptember,nearPawnee.CombinedwiththeM5.1eventinnorthwestOklahomainFebruary,andanM5.0earthquakenearCushinginNovember,theseeventsensuremoreseismicenergywillbereleasedin2016thaninanyyearinthestate’shistory.Morethan95%oftheseearthquakesoccuroveronly~17%oftheareaofOklahoma.Seismicactivityoccurredintwomainregions,aCentralzonetotheeastofthemajorNemahaFault,comprisingpartsofninecountiesmostlynorthofOklahomaCityandWestofTulsa,andaNorthwesternzonewestofthefault,comprisingpartsofsixcounties.

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Thepatternofincreasedearthquakeactivityisgenerallyattributedtoincreasedinjectionofsalineformationwaterco-producedalongwithoilandgasinsaltwaterdisposalwells.MostoftheinjectionwasintothecommonlyunderpressuredandrelativelypermeableAr-buckleGroup,whichliesdirectlyontopofPrecambriancrystallinebasement(forexample,WalshandZoback,2015).PressurecommunicationfromtheArbuckletofaultsinthebasementisinterpretedtohavereducedeffectivenormalstressonthefaults.ThisstressreductionallowsfaultsalignedfavorablywithrespecttothestressfieldinOklahoma(SHMax=N85°E)tomove.Chapter2describesinmoredetailtheearthquakepatternsandthestateoftheseismicnetworkthatrecordstheearthquakedata,includingtheimprovementscarriedoutwiththesupportoftheRPSEAandmatchingfunds.TheOklahomaGeologicalSurvey(OGS)located6,668earthquakesin2015,in34countiesinOklahoma,and3,922in2016in30counties(throughNovember22);thenumberfor2015isthegreatestnumberofearthquakesthathaveoccurredinasingleyearinOklahoma’srecordedseismichistory,whereastheratein2016reflectsasignificantdeclineinearthquakefrequency.Oftheearthquakesreportedin2015,1533wereofmagnitude2.8orgreater(M2.8+),903wereM3.0+,and27wereofM4.0+.OftheearthquakesreportedbyNovember30,2016,976wereM2.8+,596wereM3.0+,and14wereofM4.0+.Seismicitywasconcentratedincentralandnorth-centralOklahomawithalmost96%oftheearthquakeseachyearlocatedintwelvecounties(Alfalfa,Garfield,Grant,Lincoln,Logan,Major,Noble,Oklahoma,Pawnee,Payne,WoodsandWoodward).TheOGScatalogisreasonablycompletetoaminimummagnitudeof2.0duringmuchofthetimethattheOGShasoperatedaseismicmonitoringnetwork-1977toabout2013.How-ever,withtheincreasedrateofearthquakesin2014and2015,analysistothatlevelofde-tectionwasnotpossibleandoureffortsfocusedoncompletenessforaminimummagni-tudeof2.5.TheseismicityrateforOklahomacontinuedtoincreaseinearly2015.AplotofdailyratesofearthquakesaboveM2.8showsapeakinthe180-daymovingaverageabove4.5/dayinJuneof2015.Afterthattime,theratedeclineduntilearly2016,thenroseuntilApril,thendeclinedrapidlytolessthan2.4/day.The30-daymovingaverageshowstheepisodicnatureoftheseismicity,whereasthe180-daymovingaveragedisplaysthelonger-termtrend.Inthefirstfewmonthsof2014,theOGSaddedfourtemporarystations,andoneperma-nentstationinresponsetoseveralearthquakeswarmswithincentralandnorth-centralOklahoma.InstrumentationforthreeofthesetemporarystationsaregenerouslyonloanfromtheUSGS.WereceivedinstrumentationfortheOklahomaRiskandHazard(OKRaH)networkinAugust2014andinstalled12temporarystationsincentralandnorth-centralOklahoma.TheseinstrumentswereborrowedfromtheIRISPortableArraySeismicStud-iesoftheContinentalLithosphere(PASSCAL),instrumentcenter.Twelveadditionalstations,acquiredusingmatchingfundsfortheRPSEAProjectfromtheOklahomaCorporationCommission,wereinstalledduring2015and2016.Chapter3describesthegravitymeasurementsmadeinsupportofbetterunderstandingofthecharacterofthebasementrocksofOklahoma(wheremostoftheearthquakesarelo-cated).Wecollectedgravityobservationsat3,092locationsinnorthcentralOklahomaover160fielddaysfromJune2014toJuly2016.Gravityobservationsweremadealong

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publicroadways,generallyalongsection-lineroads.Stationswerelocatedwith2-milespacingasacompromisebetweencoverageanddensitybothtofillexistinggravitycoveragegapsandtocollectagridofhigherspatialdensitystationspacing.Atotalof9,020uniquegravityreadingswerereduced,resultingin3,092gravitystationswithaccompanyingpost-processedGPScoordinates.Chapter4describesaseismictomographystudyconductedintheregionbyChenChenashisDoctoraldissertation.ItprovidesanupdatedseismicvelocitymodelforthedeepcrustanduppermantlebeneathOklahoma.Thisstudyresultsinenhancementstoourabilitytorelocateearthquakesmoreprecisely,whichisimportant,giventhatperhaps50%ofearthquakesinOklahomaoccuronfaultsthathavenotbeenpreviouslyidentified.Chenderivedtwovelocitymodelsusingnorth-centralOklahomaearthquakes.Hecreatedeachvelocitymodelwith>8000earthquakesofmagnitude2.0orgreater(M2+),and>100,000P-andS-wavepicksfromseismicrecords.Tobetterunderstandthestructuresinthecrystallinebasement,velocitymodels,gravity,andmagneticdatawereusedtoexaminethegeologicalcorrelation.Onalargescale,thevelocitymodelcorrelatestogravityanomaliesbecausedenserocksgenerallyhavehighvelocities,andviceversa.ThevelocitymodelsrevealstronglateralheterogeneitieswithinthePrecambriancrystallinebasement,whichindicatescomplexstructuresintheupperportionofthecrustinthestudyarea.MostoftheearthquakesincentralOklahomaareclusteredandpresentednortheast-south-west(NE-SW)ornorthwest-southeast(NW-SE)trendingorientationthatisconsistentwiththe~East-Westmaximumhorizontalstressstatewithintheregion.Withthe3Dvelocitymodel,thecatalogedearthquakeswererelocated.Thehigh-accuracyearthquakelocationsimprovedtheresolutionoffaultlocationsbyproducingsharperpatternsofseismicity.Furthermore,theimprovedtheearthquakelocationscanpotentiallybetterexplaintherelationshipbetweeninjectionwellsandinducedseismicity.Inaddition,theimprovementoftheearthquakelocationscanhelpidentifyprimaryfaultplanesfromfocalmechanisms,crustaldeformation,andothers.Asanexample,thestudypointstoasuiteofearthquakesintheCushingareain2014thathadpreviouslybeenrelocatedbytheU.S.GeologicalSurveyalongaWNW-ESEtrendingalignment,suggestingapreviouslyunidentifiedfaultoptimallyorientedforslip.Usingthenewvelocitymodel,theseearthquakeswerere-evaluated,andappeartolieonaNE-SWtrend.Resolutionofthisdifferencewillbecriticalifwearetounderstandpatternsofseismicityondeeplyburiedfaults.Chapter5describesagravimetricmodelforportionsofOklahomaandKansas(withsmallportionsofArkansasandMissouri)thatrepresentsintegrationofallthedatawehaveassembled.Thelargerregionalmodelisrequiredtoadequatelyrepresentthegravityfieldintheprojectarea.Thegeologiccharacteroftheuppercrystallinebasementcanbeestimatedandtestedusingageologicallyandstatisticallyconstraineddensityinversionofthreedimensional(3D)free-airgravitydataandageologicallyconsistent3Ddensitydistributionofknownandexpectedgeologicfeaturesaboveandbelowtheuppercrystallinebasement.Usingpublishedformationisopachmodels,a3Dgeologicmodelisbuiltthatisconsistentwithknownandexpectedgeologiccharacteristics.Asmoregeologic

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informationbecomesavailable,theexpectedgeologicformationmodelcanbeimprovedtoreflectthesedatawhilemaintainingconsistencywithboththeregionalandlocalgeologicmodel.TheResidualFreeAirGravityAnomalyresultingfromthemodelillustratesthecomplexityofthebasementgeologybetweentheMid-ContinentRift,(MCR)inKansas,andtheSouthernOklahomaAulacogen,(SOA).AssociatedwiththesetwomajortectonicfeaturesareparallelgeologicstructuresliketheNemahaUpliftandAmarilloUpliftandtheAnadarkobasin.Also,thereareadditionalassociatedstructuresthroughoutOklahomaliketheWilzettaFaultzoneandrelatedsmallerconjugatefaultzones.AlthoughOklahomasuffersfromverysparsesamplingforgravityandmagneticfields,therearerecognizableboundariesthatappeartocorrespondwelltofaults,bothmappedandblind.Therearealsofaultandseismicfeaturesthatdonotappeartoshowinthepotentialfieldmaps.Additionaldata,augmentedbyseismicreflectiondatafromoilandgascompanies,couldsignificantlyimproveourunderstandingofthebasementstructureandthepotentialconnectiontotheoverlyingArbuckleGroupsedimentaryrock.StudiesunderwaysupportedbytheGovernorofOklahomamayproducesuchintegration.Chapter 6presentsthemathematicalbasisforcharacterizationofreservoirsliketheAr-buckleGroupsedimentaryrock,andforpressureresponseanalysistoidentifyhighlycon-ductivefluidmigrationpathwaysinthesubsurfacefrominjectionwellpumpingtests.Inthiswork,wedocumentalowfrequencyasymptoticapproachtointerpretthesepumpingtests.Theworkflowdescribedheredependsonconstructinganappropriateinitialsubsurfacesimulationmodelandadjustingthevaluesoftheuncertainmodelvariablessothatthemodelperformanceisinreasonableagreementwithactualmeasurements.TheapproachalsocalculatessensitivitiesofresultstovariationsininputparametersbytwomethodsThefirstisasemi-analyticalapproach,fromthelowfrequencyasymptoticapproach.thesecondisanumericalsensitivitycalculationderivedbyperturbingeachgridcellpermeabilityvaluebyasmallvalueandsolvingthefullfieldsimulationtoobtainchangesinthepredictedbottomholepressureattheobservationwell.Theapproachdescribedinthischapterallowsforahigh-resolutionreconstructionofconductivepathwaysinthesubsurfaceforfluidmigration.Consequently,intheabsenceofothergeophysicalmeasurementsorgeologicinterpretation,itprovidesasoundapproachtoaddressingconcernsoverthemigrationofinjectedwateranditsroleininducedseismicity.Chapter 7providesanapplicationofthismethodtotheproblemofinducedseismicity.Theobjectiveofthisstudyistodeduceatemporalandspatialcorrelationbetweensalt-waterinjectionandearthquakefrequencyusingnumericalmodels.Itattemptstoaddresssomekeyconcerns,including:

• Isthereacriticalinjectionratebelowwhichseismicitymaybemanaged?• Whatistheoptimaldistanceforinjectionwellsfromafault?• Doesthefaulttransmissibilityplayaroleingoverninginducedseismicity?

ThemodelgridemployedtounderstandporepressurevariationsinresponsetofluidinjectionintheOklahomaCityFieldcoversavolume35by35by6km,withaninjectionwellinthecenterofthemodel,andcontainingfourfaultsatvaryingdistancesfromthewellbore.Faultproperties(suchastransmissibilitycontrastwiththecountryrock)andinjectionrates,arevariedindifferentsimulationsrunfortenyears.Resultingchangesin

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stressondifferentfaultsarecalculated,usingrockpropertiesforArbuckleGroupsedimentaryrocksandregionalstressesrepresentativeofcentralOklahoma.Thesimulationresultsindicatethatamaximumchangeinthepressureofcloseto12psiaisobservedatadepthof5.4kmfromthesurfaceadjacenttothefaultthatis500mawayfromtheinjectionwell.Suchapressureincreaseinafaultatthisdepthmaybesufficienttotrig-germovementoncriticallystressedfaultsappropriatelyorientedtotheregionalstressfield.Chapter 8presentsresultsofanintegratedrockmechanicsstudy.AlmostallstudiesontheincreasedseismicityincentralOklahomahavefocusedonporepressureeffectswithoutexplicitconsiderationoflarge-scalerockmassdeformation.Inthisstudy,wehavedevel-opedalarge-scalegeomechanicalconceptualmodelforafaultsystemandassessitsre-sponsetosaltwaterinjection.ThisportionoftheRPSEAProjectaimedtounderstandtheeffectofwaterinjectiononporepressureincreaseanditsconsequenceswithintheWilzettafaultzonenearPrague,Oklahoma.Thestudyareaselectedformodelingsaltwaterinjection,encompassedapproximately460squarekilometers(approximately22×23km).Themodelconsistedofsevenlayers;threeofthemarethetargetofinjection(theHuntongroup,theSimpsongroup,theArbucklegroup)andthebottomlayer(thebasement)isthelocationofmostearthquakes.Themodelincludedtwomajorfaults;theWilzettafault(WFZ)andtheMeeker-Praguefault(MPF).Zonessurroundingthefaultswererefinedtomoreaccuratelyreflectthefaultzone.Wesimulatedthehydraulicoverpressuresandpotentialforinducedseismicityduringhydraulicinjection.Afterlettingthesystemreachequilibrium,injectionwascommencedandcontinuedfor19years(1993to2011)usingreporteddata(injectionrateandwellpressure).Wemonitoredchangeofstressconditionandredistributionoftheporepressureinthedomain,anddisplacementalongthefaultstoevaluatethepossibilityofinducedseismicity.Modelresultssuggestthatinjectioncanchangetheinitialporepressurebyasignificantamount(6MPa)alongthefault(fortheassumedboundaryconditions),whichreducestheeffectivestress,andresultininduceddisplacementsintheXandYdirectionsafter14years.Theinduceddisplacementssuggestthepotentialforearthquakes.Thestudyalsocarriedouttestsofrelevantrocktypes,andconstructedfailureenvelopesfortheserocks.Althoughfullintegrationofthepropertieswasnotcompleted,theresultstodatesuggestthatreasonableparametervaluesinwell-constructedmodelscanprovidevaluableunderstandingoftheprocessofinjection-inducedseismicity.Chapter 9tabulatestheTechnologyTransferactivitiesconductedduringthelifeoftheproject.GiventhefeedbackfromtheWorkshop:SeismicityinOklahoma,heldSeptem-ber7-8,2016attheMoore-NormanTechnologyCenterinNormanOK,thiswasthemostproductiveoftheseactivities.ResearchersfromacrosstheU.S.withaninterestininducedseismicity,especiallyinOklahomaandadjacentstates,cametogetherfortwodaysanddis-cusseddiverseaspectsoftheissue.TheprojectreceivedfavorablecommentscomparingtheworkshoptoanearlieroneconductedbytheSocietyofExplorationGeophysicistsandtheSocietyofPetroleumEngineersinFortWorthinearly2016.ApreviousNationalSeismicHazardWorkshoponInducedSeismicityinNovember,2014,hostedjointly

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withtheUSGS,alsobroughtawidevarietyoftechnicalpersonneltogethertodiscussavarietyoftopicsonunderstandinginducedseismicitywithafocusongeneralriskfrominducedearthquakes.Theprojectresultin11publications,19professionalpresentationswithpublishedabstracts,40presentationsforawidevarietyoforganizationsmostlyinOklahoma.ProjectinvestigatorsattendednumerousmeetingsofaWorkingGroupoftheOklahomaIndependentPetroleumAssociation,andinteractedwithindustrygroupsonatleastfiveoccasions.StaffalsometwithStategovernmentstaffattheGovernor’sCoordinatingCouncilonSeismicity,theSecretaryofEnergyandEnvironmentDirector’smeetings,presentedattheGovernor’sEnergyConference,andpresentedtoInterimstudygroupsoftheOklahomalegislature.TheyalsometonseveraloccasionswithU.S.GeologicalSurveystaff,andvisitedtheNationalEarthquakeInformationCenter.ThePrincipalInvestigatoralsopresentedprojectresultsattwoRPSEAsponsoredmeetings.

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1. PatternsofInducedSeismicityinCentralandNorthwestOklahoma

JeremyBoak,Director,OklahomaGeologicalSurvey,MewbourneCollegeofEarthandEnergy,UniversityofOklahoma,NormanOK73019

Summary

Oklahomaexperiencedanaverageof1.6earthquakesofMagnitude3orgreater(M3.0+)fromthe1980sthrough2008.Sincethattime,seismicityhasincreasedto903M3.0+earthquakesin2015.Earthquakefrequencyhasdeclinedin2016;however,Oklahomaex-perienceditslargestearthquake,aM5.8eventinSeptember,nearPawnee.CombinedwiththeM5.1eventinnorthwestOklahomainFebruary,andanM5.0earthquakenearCushinginNovember,theseeventsensuremoreseismicenergywillbereleasedin2016thaninanyyearinthestate’shistory.Morethan95%oftheseearthquakesoccuroveronly~17%oftheareaofOklahoma(Figure1.1).Seismicactivityoccurredintwomainregions,aCentralzonetotheeastofthemajorNemahaFault,comprisingpartsofninecountiesmostlynorthofOklahomaCityandWestofTulsa,andaNorthwesternzonewestofthefault,comprisingpartsofsixcounties.

Figure1.1:LocationofearthquakesinCentralandNorthwestOklahomafrom2009through2015,fromthecatalogoftheOklahomaGeologicalSurvey(OGS).ThemapalsoshowsidentifiedfaultsfromDaroldandHolland(2015).Reddotsareepicentersofearthquakesofmagnitude(M)<3.0,whereasbluedotsrepresentepicentersofearthquakeswithM≥3.0(M3.0+).Otherlabeleditemsaredescribedinthetext.

Alfalfa

Oklahoma

Payne

Woods

Lincoln

Grant

Garfield

Logan

Noble

Pawnee

Seminole

Okfuskee

Northwesternzone

Central zone

GalenaTownshipFault

NemahaFault

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Thepatternofincreasedearthquakeactivityisgenerallyattributedtoincreasedinjectionofsalineformationwaterco-producedalongwithoilandgasinsaltwaterdisposalwells.MostoftheinjectionwasintothecommonlyunderpressuredandrelativelypermeableAr-buckleGroup,whichliesdirectlyontopofPrecambriancrystallinebasement(forexample,WalshandZoback,2015).PressurecommunicationfromtheArbuckletofaultsinthebasementisinterpretedtohavereducedeffectivenormalstressonthefaults.ThisstressreductionallowsfaultsalignedfavorablywithrespecttothestressfieldinOklahoma(SHMax=N85°E)tomove.Thispaperdiscussestheevolutionofthisseismicity,theregulatoryactionstakentoreduceseismicitybyreducingdeepinjection,andtheimportanceofde-cliningoilpriceinreducinginjectedvolumesinadvanceoffullimplementationoftheseregulatorydirectives.BriefHistoryofInducedSeismicityinOklahoma

ThepatternofrisingearthquakefrequencyisshowninFigure1.2,whichcoverstheperiodfrom2011throughearlyNovember2016.ItshowsthedailyfrequencyofM2.8+earth-quakesaveragedmonthly.Asix-monthmovingaverageofthesevaluesisalsoplotted.Activityhadincreasedbeginningin2009,fromanannualaverageof2.9M2.8+earthquakesto24in2009,to60in2010,andto110in2011.ThesharpincreasewasassociatedlargelywiththeM5.7PragueearthquakeinNovember2011,whichdamagednumeroushomes,

Figure1.2:RelationshipofproducedwaterinjectionintoArbuckleGroupsedimentaryrockstoseismicactivity.BarsindicatedailyfrequencyofearthquakesofM2.8+bymonthfrom2009throughNovember2016.NotethePragueearthquakeswarminlate2011.Brownlinerepresentsasixmonthmovingaverage.Bluelineismonthlyinjectioninto684wellscompletedintheArbuckleGroupintheareaofincreasedseismicactivityfor2015throughearly2016.GreenlinerepresentsOklahomacrudeoilproduction(multipliedbytentodisplaytrendsmoreclearly).

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Jan-11 Jan-12 Jan-13 Jan-14 Jan-15 Jan-16 Jan-170

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M2.8+ Earthquakes684 Arbuckle Well InjectionOK Oil Production x106 Month Moving Average

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injuredseveralpeople,andarousedasignificantdebateabouttheoriginoftheearth-quakes.AfterthePragueswarm,earthquakeactivityslowedin2012(2.8+=63),butroseagainin2013(M2.8+=184)andstillmorein2014(M2.8+=951),leadingtostrongpoliti-caldebateandprotests.Seismicactivityclearlydevelopedintwomainareas,oneinnorthcentralOklahoma,andtheothertothenorthwest,acrosstheNemahaFault.Bothareashaveseendevelopmentofoilandgasplaysthatproducedverylargeamountsofwater,whichwasdisposedofinUn-dergroundInjectionClassIISaltWaterDisposalwellsinthesameareaastheproduction.Injectionvolumesreached1.5billionbarrelsin2014(Murray,2015).Therapidincreaseininjectioninthe14countieswhere>95%oftheseismicactivityoccursisalsoillustratedinFigure2.Seismicityincreasedfirstinthesouthernpartofthecentralarea,thenexpandednorthwardthenwestwardintothenorthwesternarea.Bytheendof2014,when1,533M2.8+earthquakeshadoccurred,theOklahomaCorpora-tionCommission(OCC)begantoacttoshutinsomedisposalwells,andtoreduceinjectioninothersinsensitiveareas.Inearly2015,theyrequestedthatoperatorsofabout500injectionwellsintheareaofgreatestseismicactivityshowtheywerenotinjectingdirectlyintothebasement,plugbackoutofthebasement,orcutinjectionby50%.Alsoinearly2015,theOklahomaGeologicalSurvey(OGS)putoutapositionstatementthatclearlyat-tributedtheincreasedseismicactivitytodeepinjectionofproducedwaterthroughpres-surecommunicationtothedeepbasement(AndrewsandHolland2015).Additionalac-tionstakengenerallyinresponsetoearthquakesofM4.0+calledforreductionofinjectioninmanyofthesesamewells.Figure1.2alsoillustratesinjectionratesfrom684wellscompletedintheArbuckleGroupwithintheseismicallyactivezonethatreportedinjectiondatafor2011through2016inre-sponsetoacceleratedreportingrequestedbytheOCC.Itdocumentsasubstantialdecreaseininjectionbeginningattheendof2014,largelydrivenbymarketforcesreactingtothesharpdeclineofoilpricethrough2014.AlsoshownonthechartisthemonthlyOklahomacrudeoilproductionfromtheU.S.DepartmentofEnergy’sEnergyInformationAdministra-tion(U.S.EnergyInformationAdministration,2016).ItshowsaverymodestdeclineincrudeoilproductioninOklahoma,in2015,butincreasingproductionin2016.Thistrendsuggeststhatotherplaysaretakingtheplaceofproductionlostinthewater-richplaysthatgeneratemuchofthesaltwaterdisposedintheseismicareaofinterest.DespitereductionsdirectedbytheOCC,theearthquakecountclimbedto1533M2.8+earthquakesbytheendof2015.InNovember2015,asurgeinseismicactivitybeganonafaultinsouthernWoodsCountymorethan12kmawayfromthemainareaofinjectioninnorthernWoods,Alfalfa,andGrantCounties.About75%ofallseismicmomentreleasedinOklahomainJanuaryand85%inFebruarycamealongwhathasbeenlabeledtheGalenaTownshipFault(seeFigure1.1).ThreeM4.0+earthquakesinthefirstweekinJanuary,anM5.1earthquakeinFebruary,andthreeM4.0+aftershocksofthatearthquakeinJulywerethemostsignificanteventsthroughAugust2016.Figure1.3(Yecketal.,2016)showstheepicentersofearthquakesontheGalenaTownshipFault,aswellastheareaofhigherinjectionratewellstothenorth.Yecketal.(2016)con-cludedthatseismicactivityinthisareawasdrivenbyinjectioninthehighratedisposal

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wellsshowninthenorthernpartofthearea.Theyalsopointoutthat,whereasseismiceventsoccurrednearthehighinjectionratewells,noearthquakewasaslargeasthemainshockontheGalenaTownshipFault.Theyconcludethatthemagnitudeofinducedearth-quakesisdeterminedbythecharacteristicsofthefault,andnotthedegreeofporepres-sureenhancementfrominjection.Thisinferencesuggeststhatchangesininjectionratewillmostlikelyaffectthefrequencyofearthquakes,notthemagnitude.ElsewhereintheearthquakeAreaofInterest,earthquakefrequencydeclined.Thedeclinebeganinmid-2015inthecentralarea,andsomewhatlaterinthenorthwestarea.IntheCentralarea,whichexperienced14M4.0+earthquakesin2015,anM4.2earthquakeonNewYearsDay2016wasfollowedbyanintervalof88dayswithnoM4.0+earthquakes.Thenorthwestareaexperiencedapulseoflargerearthquakesinlate2015,amidatrendofgenerallydecreasingactivity.However,activityontheGalenaTownshipFaultledtoanoverallincreaseinM2.8+earthquakes.BeginninginMay2016,therateofM2.8+earth-quakesbeganarapiddecline.The180-dayrunningaverageofM2.8+earthquakesperdaypeakedinmid-2015atavaluenear4.5.Ithaddeclinedtoabout4.0bylateApril.Fromthere,itdeclinedtoabout2.3bytheendofSeptember,despiteburstsofactivityintheNorthwesternzoneinJulyandthePawneeearthquakeswarminSeptember.OvertheLaborDayweekend2016,aM5.8earthquakeoccurredinPawneeCounty,ontheeasternedgeoftheearthquakeAreaofInterest,inacountythathadexperiencedrelatively

Figure1.3:LocationofGalenaTownshipFaultandearthquakesoftheFairviewcluster(inWoodsandMajorCounties),aswellaszoneofhighrateinjectionwellsinGrantandAlfalfaCounties,~12kmaway.FromYeck,etal.,(2016)

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fewearthquakesovertheperiodofincreasedactivity,andwhoseneighbor,OsageCounty(administeredbytheOsageNation)hadexperiencedalmostnoearthquakes(Figure1.4).ThisearthquakecausedlocalizeddamageinPawnee,butwasfeltthroughoutmuchoftheU.S.mid-continent.Thelocationofthemainshockandearlyaftershocksplaceditonapreviouslyidentifiedfault(seeDaroldandHolland[2015]).However,subsequentafter-shocksdefinedanadditionalpreviouslyunidentifiedfault,andtheOCCwasforcedtoreviseitsinitialorder,shuttinginsomeadditionalwells,butalsochangingthewellsthatweredi-rectedtocutbackoninjection.AdditionalwellsinOsageCountywerealsoshutin.TheU.S. EnvironmentalProtectionAgency,whichregulatessaltwaterdisposalintheCounty,fol-lowedtheleadoftheOCCinitsaction.Subsequently,aM5.0earthquakeoccurredonNovember7,2016nearthetownofCushingOklahoma,bringingthetotalofM5.0+earthquakesfor2016tothree,anumberunprece-dentedinthestate’shistory.AllfourM5.0+earthquakesinrecenttimes(includingtheM5.7Pragueeventof2011)haveoccurredneartheedgesoftheAreaofInterest.Theoc-currenceofthreeM5.0+earthquakesagainstapatternofdeclinefornearlyallothermagni-tudegroupsraisespuzzlingquestionsaboutthetrend,atleastinthepubliceye.Forexam-ple,thenumberofM2.8+earthquakesasofNovember22was967.Simplelinearextrapo-lationwouldestimatetheyearendvalueat~1100,areductionofnearly30%from2015.

Figure1.4:Locationsofearthquakeepicenters(circles)oftheSeptember3,2016Pawneeearthquakeanditsaftershocks,aswellassaltwaterinjectionwells(triangles)directedtoshutin(areaoutlinedbypinkline)orreduceinjection(areaoutlinedbyblueline)byOklahomaCorporationCommission.ShadedareaistheportionofOsageCounty(administeredbytheOsageNationandtheU.S.EPA)affectedbychangesininjection.FigurefromOklahomaCorporationCommission.

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ForMagnitude3.0earthquakes,thecurrentcountis591,whichwouldextrapolateto~660bytheendoftheyear–areductionofmorethan200fromthe2015valueof903.ActionsoftheCorporationCommission

TheOklahomaCorporationCommission(OCC)hastakennumerousstepstoreduceinjec-tionofproducedformationwateracrossmostoftheearthquake-pronearea.Theteamad-dressingtheearthquakeissuedefinedanearthquake-proneAreaofInterestthatencom-passedaverylargefractionoftheearthquakes.Thisareaincreasedinsizeastheearth-quakescontinued,althoughithasbeenstablesinceearly2016.TheOCChasissuedaseriesofdirectivescallingforchangesininjectionpracticesandquantitiesinresponsetotheevolvingseismicactivity(seeTable1.1).Averagedepthoftheearthquakeshasgenerallybeen5.4-5.5kilometers,indicatingthatmostoftheseismicityoccurswithinthecrystallinebasementofOklahoma(Daroldetal.,2015).InjectionintotheArbuckleGroup,thestratigraphicunitthatliesdirectlyonthecrystallinebasement,hasbeenidentifiedasthelikelycauseoftheearthquakes.Thelargestfractionofthevolumeofinjectionhasbeenintothishorizon,andincreasesofporepres-sureintheArbuckleareinterpretedtohavebeentransmittedtoblindfaultsinthecrystal-linebasement.Conclusions

TheelevatedseismicactivityresultingfromearthquakesinterpretedasinducedbyoilandgasoperationsinOklahomaishighlylikelytocontinueatleastthrough2017.Howmuchthenumberofearthquakeswilldecreasein2016islikelytodependupontheactivityontheGalenaTownshipFaultandonfaultsresponsibleforthePawneeandCushingearth-quakes.Asthelargestearthquakessince2011happenedinFebruary,SeptemberandNo-vemberof2016inthesezones,thereremainslargeuncertaintyaboutthefrequencyandmagnitudeofearthquakes,andtheirpotentialfordamage.EachoftheM5.0+eventshasresultedinsomedamage.However,theresultsofinitialdamagefromamoderate(sayM4.0+)earthquakethatisaggravatedbycumulativeshakingfromthenumeroussmallerearthquakeshasnotbeenevaluated,andremainsasignificantissueforthestate.Acknowledgements

TheauthoracknowledgesthesupportofmanymembersofthestaffoftheOklahomaGeo-logicalSurvey,particularlyhydrogeologistKyleMurrayandactingleadseismologistJeffer-sonChang.TheworkofAustinHollandandAmberleeDarold,whobuiltmuchofthepre-sentOGSseismicnetworkandestablishedtheframeworkforunderstandingOklahomaearthquakes,canhardlybeoverstated.ReferenceCited

Andrews,R.D.,andA.A.Holland2015,StatementonOklahomaSeismicity,April21,2015Darold,A.P.,A.A.Holland,J.K.Morris,A.R.Gibson,2015,OklahomaEarthquakeSummaryReport2014,OklahomaGeologicalSurveyOpen-FileReportOF1-2015,February2015Darold,A.P.,andA.A.Holland,2015,PreliminaryOptimalOklahomaFaultOrientationsOklahomaGeologicalSurveyOpenFileReportOF4-2015,July2015.

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Murray,K.,2015,ClassIISaltwaterDisposalfor2009–2014attheAnnual-,State-,andCounty-ScalesbyGeologicZonesofCompletion,Oklahoma,OklahomaGeologicalSurveyOpen-FileReportOF5-2015,December2015.Walsh,F.R.andZoback,M.D.,2015,Oklahoma’srecentearthquakesandsaltwaterdis-posal,Sci.Adv.2015;1:e1500195Yeck,W.L.,M.Weingarten,H.M.Benz,D.E.McNamara,E.A.Bergman,R.B.Herrmann,J.L.Rubinstein,andP.S.Earle(2016),Far-fieldpressurizationlikelycausedoneofthelargestinjectioninducedearthquakesbyreactivatingalargepreexistingbasementfaultstructure,Geophys.Res.Lett.,43,doi:10.1002/2016GL070861.

Table1.1:DirectivesoftheOklahomaCorporationCommissionfortheearthquakeproneareaofOklahoma,withnumbersofwellsaffectedandreductionsininjectionvolume

DirectiveDate#WellsAffected ShutIn Reduced

TotalReduction(BPD) ActionArea

March18,2015 347 FullAreaofInterestJune17,2015 1 1 0 375 OlmsteadJuly15,2015 211 ExpandedAreaofInterestJuly28,2015 3 1 2 x Crescent

August3,2015 23 0 23 x Logan-PayneTrendSeptember17,2015 13 3 10 6,126 Cushing3.7October16,2015 x Cushing4+

November16,2015 x FairviewNovember19,2015 x CherokeeCarmenNovember19,2015 x CrescentDecember3,2015 x ByronDecember3,2015 x MedfordDecember29,2015 x EdmondNovember7,2015 x NMedfordJanuary12,2015 x FairviewCherokeeTrend

February16,2016 195 195 400,000OKWesternReductionArea-reductionto2012levels

March7,2016 398 398 400,000OkCentralReductionArea-reductionto2012levels

March7,2016 77 77 WellsaddedtoexpandedAOIAugust17,2016 21 2 19 20,000 Luther-Wellston

September3,2016 48 27 21 40,000 Pawnee5.8November3,2016 20 4 16 12,000 Pawnee4.3November7,2016 72 7 65 33,000 Cushing5.0

911,501x=PlanRemovedwithregionalplanimplementation;Shut-inwellsremainedshut-in

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DescriptionofRPSEATask6–SeismicMonitoring:TheSubcontractorshallinstallandoper-ate12seismicstationswithinstudyarea.DatashallbesentinrealtimetotheOklahomaGeologicalSurvey(OGS)seismicmonitoringsystemandprocessedforroutineproductssuchashypocentrallocationandfocalmechanism.Thestationsshallbelaidoutonaroughgridinculturallyquietlocations.These12stationsshallbeaugmentedbyfourportableseismicmonitoringsystemsfordetailedstudies,astheyareavailabledependingonseis-micitypatternsandparticularareasofinterest.Datafromthisseismicmonitoringeffortshallalsobeintegratedintothe3DEarthInterpretation(Task9.0)asseismictomography,hypocenterandstressorientations,andotherseismicimagingtechniques.ThereportappendedbelowsummarizesearthquakemonitoringactivitiesinOklahomadur-ing2015and2016,withreferencetoactivitiessupportedbytheRPSEAProject.

2. OklahomaEarthquakeSummaryReport2015-16

JeffersonChang,JeremyBoak,NoorulanGhouse,FernandoFerrerVargas,AndrewThielOklahomaGeologicalSurvey,SarkeysEnergyCenter,Rm.N-131100EastBoydSt.,Norman,Oklahoma73019-0628

SummaryTheOklahomaGeologicalSurvey(OGS)located6,668earthquakesin2015,in34countiesinOklahoma,and3,922in2016in30counties(throughNovember22;seeFigure2.1);thenumberfor2015isthegreatestnumberofearthquakesthathaveoccurredinasingleyearinOklahoma’srecordedseismichistory,whereastheratein2016reflectsasignificantde-clineinearthquakefrequency.Oftheearthquakesreportedin2015,1533wereofmagni-tude2.8orgreater(M2.8+),903wereM3.0+,and27wereofM4.0+.OftheearthquakesreportedbyNovember30,2016,976wereM2.8+,596wereM3.0+,and14wereofM4.0+.Seismicitywasconcentratedincentralandnorth-centralOklahomawithalmost96%oftheearthquakeseachyearlocatedintwelvecounties(Alfalfa,Garfield,Grant,Lincoln,Logan,Major,Noble,Oklahoma,Pawnee,Payne,WoodsandWoodward).TheOGScatalogisreasonablycompletetoaminimummagnitudeof2.0duringmuchofthetimethattheOGShasoperatedaseismicmonitoringnetwork-1977toabout2013.How-ever,withtheincreasedrateofearthquakesin2014and2015,analysistothatlevelofde-tectionwasnotpossibleandoureffortsfocusedoncompletenessforaminimummagni-tudeof2.5.TheseismicityrateforOklahomacontinuedtoincreaseinearly2015.AplotofdailyratesofearthquakesaboveM2.8(figure2.2)showsapeakinthe180-daymovingav-erageabove4.5/dayinJuneof2015.Afterthattime,theratedeclineduntilearly2016,thenroseuntilApril,thendeclinedrapidlytolessthan2.4/day.The30-daymovingaver-ageshowstheepisodicnatureoftheseismicity,whereasthe180-daymovingaveragedis-playsthelonger-termtrend.Thelargestearthquakesin2015weremagnitude4.7eventsinGrantandAlfalfaCounties.ByNovember30,2016,Oklahomahadrecordedthreeearthquakesofmagnitudegreaterthan5–aM5.1eventFebruary13,2016northwestofFairviewinWoodsCounty,aM5.8

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Figure2.1a:EarthquakeslocatedbytheOklahomaGeologicalSurveyin2015.Bluedotsareearthquakesofmagnitudelessthan3.0;Greendotsaremagnitude3.0-4.0;RedDotsaremagnitudegreaterthan4.0.

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Figure2.1b:EarthquakeslocatedbytheOklahomaGeologicalSurveyin2016.Bluedotsareearthquakesofmagnitudelessthan3.0;Greendotsaremagnitude3.0-4.0;RedDotsaremagnitudegreaterthan4.0.

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eventSeptember3,2016nearPawneeinPawneeCounty,andaM5.0eventNovember6,2016nearCushinginPayneCounty.Thesethreeearthquakesrepresentedthelargest,se-condlargestandfourthlargestearthquakesinrecordedhistoryforOklahoma,accountedforapproximately81%oftheseismicmomentreleasedin2016(toNovember30),anden-suredthat2016wouldbetheyearofgreatestseismicenergyreleaseinOklahomahistory.TheFebruaryeventoccurredalongwhathasbeeninformallytermedtheGalenaTownshipFault,andextendedthetraceofafaultpreviouslymappedinMajorCountyintoWoodsCounty.TheSeptember3rdeventoccurredattheintersectionofapreviouslyidentifiedfaultwithafaultthatwasdefinedbytheseismicactivitythatfollowedthemainshock.TheNovember6theventoccurredonafaultthathadpreviouslybeenactiveinOctober2015.Table2.1liststhenumberofearthquakesofmagnitude2.5orgreater(M2.5+)in2015,bymonthandbycounty,withtheoveralltotalbeing3,309events.Twenty-fivecountiesarerepresented,butonlyseventeenhavemorethanfiveeventsofthismagnitude.Individualcountiesandtheentirestateshowremarkablemonthtomonthvariability,reflectingtheepisodicnatureofseismicity.GrantCountyshowedthehighestearthquakefrequencyforsevenoftwelvemonths,andfortheentireyear,withmorethanonequarterofalleventsoccurringinthiscounty.LoganCountyhadthehighestcountfortwomonths,andwasse-condhighestfortheyear.Alfalfa,Garfield,andPayneCountyledinonemontheach,andwerethird,fourth,andsixthinearthquakefrequencyfortheentireyear.NobleCounty,wasthefifthinearthquakefrequency,butledinnomonth.

Figure2.2.EarthquakerateinOklahomaforearthquakesofM2.8+,showingdailyrateaswellas30-dayand180-daymovingaverages.

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Table2.2liststhenumberofM2.5+earthquakesfor2016(toNovember30,2016),withtheoverallcountbeing1,992.Thesenumberswereincreasingregularlyinthelatterhalfoftheyearastheexpandedseismicteamsoughttodrivethecompletenesslevelofthecatalogdownto2.5andlower.Twenty-ninecountiesarerepresentedinthetable,butnineteenrecordedmorethanfiveevents,evenintheshorterperiodthanfor2015.WoodsCounty,locationoftheGalenaTownshipFault,whichproducedanM5.1earthquakeinFebruary,toppedthelistforearthquakefrequency.Itaccountedforslightlymorethanonefifthofthetotalnumber,andledinfivemonthlycounts.GrantCountywassecond

Table2.1.NumberofM2.5+earthquakesreported,listedbycountyandmonthfor2015,sortedbytotalearthquakes,frommosttoleast.

County Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total

Grant 106 54 120 75 60 56 49 75 32 47 131 65 870Logan 54 22 63 76 30 74 56 27 17 12 29 19 479Alfalfa 49 57 28 23 28 34 44 27 24 13 56 27 410Garfield 17 7 24 35 26 82 29 21 25 24 17 11 318Noble 37 23 47 46 22 24 14 14 25 26 18 16 312Payne 21 16 47 12 15 11 15 16 54 26 10 12 255Woodward 3 1 34 26 36 7 11 3 12 2 6 4 145Pawnee 15 2 5 4 8 24 18 5 8 11 4 5 109Woods 2 3 4 1 10 10 2 8 8 9 22 22 101Lincoln 6 4 11 6 11 14 10 9 6 5 3 15 100Oklahoma 3 1 9 8 6 11 6 8 8 6 3 24 93Major 3 3 1 1 6 6 3 5 13 11 6 3 61Grady 3 1 2 2 3 11Pottawatomie 1 1 4 1 2 9Kay 1 1 3 1 1 1 8Seminole 1 3 1 5Kingfisher 1 1 3 5Okfuskee 1 1 1 3McClain 1 2 3Canadian 1 1 1 3Blaine 3 3Stephens 1 1 2Osage 1 1 2Love 1 1

Pittsburg 1 1

GrandTotal 320 194 401 315 259 356 266 225 233 195 318 227 3309

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overall,butdidnottopthelistforanyonemonth.Oklahoma,GarfieldandAlfalfaCountiesrankedthird,fourthandsixthrespectively,eachleadinginonemonth.LoganCounty,rankedfifth,didnotleadinanymonth.Pawnee,siteofthelargestearthquakeoftheyear,ledonlyinSeptember,themonthoftheM5.8earthquake.

Table2.2.NumberofM2.5+earthquakesreported,listedbycountyandmonthfor2016(toSeptember28,2016),sortedbytotalearthquakes,frommosttoleast.

County Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Total

Woods 101 87 29 24 19 28 44 13 16 17 4 382Grant 57 31 26 24 19 17 16 17 32 21 12 272Oklahoma 41 40 9 27 17 7 10 5 11 5 6 178Garfield 2 28 21 10 23 14 24 26 11 7 2 168Logan 29 17 9 15 17 12 23 4 13 4 5 148Pawnee 3 5 2 9 2 8 6 71 18 21 145Payne 26 28 8 7 11 6 17 4 19 1 12 139Alfalfa 22 5 26 7 29 9 13 3 9 2 6 131Noble 12 8 9 14 4 7 10 12 21 7 6 110Woodward 4 11 14 9 6 14 4 6 7 15 3 93Major 10 5 7 13 1 6 1 4 4 21 13 85Lincoln 6 3 7 12 2 2 4 8 3 5 3 55Kay 1 5 8 4 6 2 1 27Kingfisher 1 2 1 7 1 12McClain 3 8 11Pottawatomie 1 1 1 1 1 5Grady 2 2 1 5Coal 1 1 1 1 1 5Canadian 5 5Dewey 1 1 3 5Seminole 1 1 1 3Hughes 1 1 2Okfuskee 1 1Pittsburg 1 1

Blaine 1 1

Osage 1 1Cherokee 1 1

Harper 1 1

GrandTotal 314 272 176 184 161 146 183 106 224 126 100 1992

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EarthquakeProcessingandAnalysisTheOGShasusedtheSEISAN(HavskovandOtte-moller,1999)earthquakeanalysispackagesince2010.Theregionalvelocitymodelusedtodeter-minethelocationofearthquakesinOklahomaisshowninTable2.3.WecurrentlyuseaVp/Vsra-tioof1.73fortheregionalvelocitymodel.TheregionalmodeldoesareasonablygoodjobthroughmostofthestateofOklahoma.SEISANhasthecapabilitytocalculatemomentmagnitude(MW)fromtheshapeofthedisplace-mentspectra(Abercrombie,1995;Brune,1970).TheOGSbeganroutinelydoingMWanalysisin2014forearthquakesofaninitiallocalmagnitude(ML)of3.8orgreater.TherearemanysmallerearthquakesforwhichanMWhasalsobeencal-culated.Ingeneral,MW’scalculatedbytheOGScomparequitewelltothosedeterminedbytheUnitedStatesGeologicalSurvey(USGS)Na-tionalEarthquakeInformationCenter(NEIC),whichgenerallyareonlydeterminedforearthquakesofmagnitude4.0orgreater.TheMWmagnitudestendtobesmallerthantheMLmagnitudescalculatedbytheOGS.BothofthesecalculationsaretrackedintheearthquakereportingintheOGScatalog,whichisavailablefor2015and2016inavarietyofformatsat

http://www.okgeosurvey1.gov/pages/earthquakes/catalogs.phpordirectlyathttp://wichita.ogs.ou.edu/eq/catalog/2015/andhttp://wichita.ogs.ou.edu/eq/catalog/2016/.

TheOGSearthquakecatalogispreliminaryandsubjecttochangeasfurtheranalysisoccurs.Theinformationinthecatalogmaychange,andisalwaysthemostup-to-dateattheabovelinks.ForanearthquaketobereportedintheOGScatalog,theremustbeidentifiedphasearrivalsfromatleastfourseismicstationsincludedinthelocationsolutionandtheearth-quakemusthaveoccurredwithinOklahoma.Inaddition,theOGSroutinelyrelocatesearthquakesusingHYPODD(WaldhauserandEllsworth,2000).Theserelocationsareinthestaticcopyofthecatalog.Adiscussionofparametersusedfortherelocationsandthereasonsforthesechoicesisbeyondthescopeofthisreport,butwewillprovidethisinfor-mationtothosethatmaybeinterested.SEISANallowsthecalculationoffirstfocalmechanismsusingavarietyoftechniquesin-cludingFPFIT(ReasenbergandOppenheimer,1985),HASH(HardebeckandShearer,2002),andFOCMEC(Snokeetal.,1984).Allthesetechniquescontinuedtobeusedtode-terminefocalmechanismsforearthquakesinOklahomaduring2015and2016.During2015and2016,???focalmechanismsweredeterminedmostlyforearthquakesofmagni-tude3.0andgreater.

Table2.3.Regional1-DvelocitymodelusedinOklahomatodeterminethelocationofearthquakes

P-Velocity(km/s) Depth(km)

2.700 0.0

2.950 0.3

4.150 1.0

5.800 1.5

6.270 8.0

6.410 21.0

7.90 42.0

8.15 50.0

8.5 80.0

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TheOGSimplemented,withthesupportoftheUSGS,acontinuouswaveformbuffer(CWB)thatallowsforthereal-timeexchangeofdatafromourdataserverusingSEEDLINK,whichcontinuestobeusedtosenddatatotheIncorporatedResearchInstitutionsforSeismol-ogy’s(IRIS)datamanagementcenter(DMC).TheOGSCWBallowsforthecontinuousar-chivingofdataanddataretrievalforearthquakestudiesandanalysis.Inaddition,theOGSbeganoperatingaquasi-real-timeautomaticprocessingsystemcalledSeiProc.TheSeiProcsystemregularlyperformscoincidencetriggeringondifferentsub-netsinOklahoma.Onceeventsareidentified,thewaveformsareprocessedbyanauto-maticpickerandassociatoralgorithm(ChenandHolland,2014).AfteraneventhasbeenautomaticallylocatedusingtheSEISANearthquakelocationalgorithm,anMLisautomati-callydeterminedforeachearthquake.SeiProcallowsanalyststoprioritizetheireffortsbybeingabletoidentifyandbeginanaly-sisonearthquakeswithanautomaticallydeterminedmagnitudeof2.5orgreater.Fur-thermore,itreducestheeffortrequiredbyanalystsformanuallylocatingverysmallearth-quakes.Routinely,locationsandmagnitudescanchangesubstantiallyuponre-evaluationbyatrainedanalystcomparedtotheautomaticsystem.Becausethepotentialforproblem-aticeventsfromtheautomaticprocessingsystem,automaticearthquakesolutionsarenotreported.Thus,topreventconfusion,thesedataareonlyusedtoguideandprioritizetheanalysisofearthquakes.EarthquakeMagnitudesThestatehasseenanincreasednumberofmagnitude4.0orgreaterearthquakesin2015comparedtoyearsprior.However,afterfurtheranalysismanyhavemagnitudesbelow4.0;thisisoftenthecaseatboththeUSGSandtheOGS.Therearemanywaystocalculatemagnitudeandthemostreliablemethodsareusuallydoneaftertheinitialreportingofanearthquakeandfurtheranalysisoccurs.Themorereliablemethodsformagnitudedeterminationmostlyaffectthelargerearthquakesandtendtoreducetheirmagnitudeslightly.MostOklahomaearthquakesarelocatedandreportedwithaninitialMLandupdatedtoaMWiffurtheranalysisisdeemednecessary(i.e.theearthquakeisestimatedata3.8MLorgreater).ThemethodusedbytheOGStocalculateMLandtheMLattenuationrelationshipusedaredocumentedinDaroldetal.(2014).Localmagnitudesoftendisagreeslightlywithothermagnituderelationships,ascanbeseeninMiaoandLangston(2007),butarecommonlyusedbyregionalnetworks.Magnitudemeasurementsareestimatesbasedonrecordedgroundmotionsandhaveuncertaintythatcanbecharacterized(CEUS-SSC,2012).TheOGSusesthespectralshapeindisplacementofthePorSphasetodeterminetheMWforearthquakesusingfunctionalitywithinSEISAN(Abercrombie,1995;Brune,1970;Caprioetal.,2011;OttemollerandHavskov,2003).TheMWmoreaccuratelyrepresentstheareaofthefaultthatrupturedandthetotalenergyreleased(HanksandKanamori,1979;KanamoriandAnderson,1975),whereastheinitialMLusesmeasuredamplitudesandmaymoreaccuratelyrepresentthegroundshakingofanearthquakeexperiencedby

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thosethatfeelit.TheOGSinitiallyreported60earthquakesatoraboveamagnitude4.0in2015and42in2016.However,aftercompletingMWanalysisandusingtheUSGSMWcal-culationsasthepreferredmagnitude,thenumberofreportedearthquakesatoraboveamagnitude4.0wasreducedto28for2015and14for2016(toNovember30,2016).ImprovementstoNetworkfromRPSEAProject

TohelpexpandandprioritizeanalysiseffortstheOGShaddevelopedandimplementedanautomaticprocessingandearthquakeevaluationsystemandupgradedtheexistingdataarchiving,retrieval,andexchangeprocesses.AdditionsandupgradestotheOGSseismicmonitoringnetworkduring2015and2016,continuedtodramaticallyimproveearthquakelocationaccuraciesandanalysis.TheconfigurationofOGSseismicstationsisshowninFigure2.3,bothbefore(2.3a)andafter(2.3b)implementationofthesystemupgradesaf-fordedbytheRPSEAProject.Inthefirstfewmonthsof2014,theOGSaddedfourtemporarystations,andoneperma-nentstationinresponsetoseveralearthquakeswarmswithincentralandnorth-centralOklahoma.InstrumentationforthreeofthesetemporarystationsaregenerouslyonloanfromtheUSGS.WereceivedinstrumentationfortheOklahomaRiskandHazard(OKRaH)networkinAugust2014andinstalled12temporarystationsincentralandnorth-centralOklahoma.TheseinstrumentswereborrowedfromtheIRISPortableArraySeismicStud-iesoftheContinentalLithosphere(PASSCAL),instrumentcenter.Twelveadditionalstations,acquiredusingmatchingfundsfortheRPSEAProjectfromtheOklahomaCorporationCommission,wereinstalledduring2015and2016.Tomeetwiththedemandsofanexpandingworkloadinallareasandtoimprovecommuni-cationwiththecommunity,theOGSaddedanactingleadseismologist,aleadseismicana-lyst,twoadditionalanalysts,andaseismictechnicianin2015and2016.However,theLeadSeismologist(AustinHolland)andResearchScientist(AmberleeDarold)bothlefttheOGSforpositionswiththeUnitedStatesGeologicalSurvey.JeffersonChangwaspromotedtoActingLeadSeismologistduringthesearchforaLeadSeismologist.InAugust2016,OGShiredJacobWaltertotheposition,withaNovember1,2016startdate.OklahomaRiskandHazard(OKRaH)NetworkOklahomaRiskandHazard(OKRaH)networkconsistsofasetoftemporaryseismicsta-tionsdeployedaspartofthisRPSEAProject,includingcostsharecontributionsfromthestateofOklahoma,theUniversityofOklahoma,andOklahomaoilandgasoperators.Forthisproject,12temporaryseismicstationsareoperatedincentralandnorth-centralOkla-homawithintheexistingseismicmonitoringnetworkoperatedbytheOGS.Eachstationconsistsofasensitiveseismometer,arecordingdevice,batteriesandasolarpanel.AlltwelveofthesestationsfeedimmediatelyintotheOGSseismicmonitoringsystem.ThedataareincorporatedintoroutineearthquakeanalysiswithinOklahomaorinsupportofotherresearchefforts.ThedataarealsoarchivedattheIRISDMC(www.iris.edu)andwillbemadeavailabletootherresearchersaftertheprojecthasbeencompleted.Onestation(KNG1)isbeingprovidedasopendataandisavailableattheIRISDMC.

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a)

b)Figure2.3.a)OGSseismicnetworkpriortoRPSEAproject.b)OGSseismicnetworkafterRPSEAprojectinstallations.TheinitialRPSEAprojectareaishighlightedintherectangle.

Therecordingsfromtheseinstruments,alongwiththeOklahomaSeismicNetwork,willbeusedtoimproveourunderstandingofactivefaultsandsubsurfacerockproperties,alongwiththesurfacegroundmotionsobservedinOklahoma.Ultimately,wehopetogainabet-terunderstandingofpotentialchangesthatmaybecausingsomeoftheearthquakeswithin

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Oklahoma.Further,current,informationontheOKRaHnetworkareavailableontheOGSseismicmonitoringwebsite.OGSOutreachandEducationEffortsTheincreasedrateofseismicityinOklahomain2014-15addedtothepotentialfuturerisktothepublic,thereforetheOGSsoughttoestablishamoreproactivestanceonearthquakeeducationandoutreachefforts.Thismultidimensionalapproachencompassedpresenta-tionstotheFederalEmergencyManagementAgency,localandstateemergencymanage-mentgroupsinadditiontoothercivicorganizations,astrongonlinepresence,activeen-gagementandopendialoguewithintheacademiccommunity,mediainterviews/state-ments,andtheproductionofhardcopypreparednessmaterials.Itisthroughtheseunder-takingsthattheOGSstayedconsistentlyvisibleandinformativetothepublic.WebsiteandSocialMediaOntheOGSwebsite(www.ou.edu/ogs/),asectionisdevotedtoinformationregardingOklahomaearthquakes.In2015and2016,theOGSwebsitepostedcurrentearthquakes,mapsoftheseismicmonitoringnetwork,earthquakecatalogues,currentandpastresearchpublications,andearthquakepreparedness/educationmaterial.Moreover,thewebsiteallowedfortheexternalreportingofearthquakesbythepublic(ReportFeelinganOklahomaEarthquake),askingseismologistsquestions(Askaseismologist)andthepostingoffrequentlyaskedquestionswithreplies(OKEarthquakeFAQ).ThehomepagedisplaysadirectlinktoourTwitterandFacebookaccounts.Twosocialmediaaccounts,Twitter’s@OKearthquakesandFacebook’sOklahomaGeologi-calSurvey–EarthquakeNotices,postthelatestinformationonOklahomaearthquakesastheyarelocatedandupdatedbyanalysts.Thecommunicationincludesthedate,time,mag-nitude,closesttown,latitude/longitude,anddepthofeachearthquake.Thenumberofsocialmediapostsgenerallycorrelateswiththenumberofearthquakesgreaterthanmagnitude2.4.Analysthoursoccurprimarilywithinworkdaysandworkinghours(8am-5pm);tweetsandFacebookpostsoccurmainlyduringthesetimes.Forearth-quakewithmagnitudesgreaterthan3.0,analystsareon-callandupdateearthquakeloca-tionsassoonaspossible,includingweekendsandholidays.TheTwitteraccount@OKearthquakescurrentlyhas3,191followers;thegeneralOGSac-count,@OKgeologyhas198additionalfollowers(total=3,389followers).TheFacebookaccountOklahomaGeologicalSurvey–EarthquakeNoticeshas2,168followers;theOkla-homaGeologicalSurveyaccounthas590additionalfollowers(total=2,758followers).AcademiaFromthemostbasictothemostadvancedlevelsofeducation,theOGSseismicgroupstrivestoextenditselfanditsknowledgetostudentsandscholarsinallareasconcerningOklahomaearthquakeeducationandon-goingresearch.TheOGSworkedwithmultipleprimary,secondary,andpost-secondaryinstitutionslastyearandheldatwodayWork-shoponOklahomaSeismicity,whichincludednumerouspresentationsandquestionandanswersessionsfortechnicalparticipantsfromFederalandstategovernment,academia,

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nationallaboratories,andtheoilandgasindustry.Thefunctionwaswellattendedwithoveronehundredfortyparticipants.Attheprimaryandsecondarylevelsofeducation,theOGSacceptedseverallocalpublicschoolinvitationstoteachand/orgivepresentationsaboutearthquakes.Alongwiththeseinvitations,level-appropriatematerialswerecreatedtoscaffoldlearningforyoungstu-dentsandpreparednessbrochureswereprovidedtostudents,teachers,andparents.Addi-tionally,toursandpresentationswereheldforstudentsattheOGSfacilitiesbothinNor-man,OklahomaandLeonard,Oklahoma.BecausethemainofficesfortheOGSaresituatedattheUniversityofOklahomaandbe-causeeducationaloutreachishighlyvalued,theOGSemploysundergraduateandgraduatestudentstocreatemutuallybeneficialrelationshipsofinnovationanddevelopment.Thesestudent-employeeshelpwiththemaintenanceofcatalogs,databases,andevenemploytheirownoriginalresearchattimes.Inturn,theireducationandresearchreceivesinputfromprofessionalsandaddsacomponentofpracticalexperience.EmployeesoftheOGSseismicgrouppublishedseveralpapersin2015and2016andattendednumerousconferencestoshareandreceiveinputforrecentseismicfindingsinOklahoma.Theycollaboratedoftenwithinstitutionsandresearchersnation-wideandpar-ticipatedintheUSGSPowellCenterWorkingGrouponInducedSeismicity.Theirpublica-tionscanbefoundonthewebsiteorinthelistprovidedinChapter9:TechnologyTransferActivities.LocalCommunitiesRepresentativesfromtheOGSseismicmonitoringprogramgavenumerouspresentationstocommunityorganizationsalloverthestate.Thesepresentationsprovidedgeneral,fac-tualinformationontheincreaseofOklahomaearthquakesandvitalinformationaboutOk-lahomaearthquakehazardandpreparedness.Bysharingthisinformationwithcivic-mindedcommunityorganizations,itistheOGS’sexpectationthatcommunityleaders(membersoftheseorganizations)willfurtherdisseminateit,ultimatelyestablishingmorepublicawareness.MediaTheOGSseismicgroupofferedmanyinterviewandmediacoverageopportunitiestolocal,nationalandglobalmedia.Throughmediaexposure,theOGSgainedyetanothermethodofcommunicationandtransparencywiththepublic.Publications2015-2016Publicationsin2015and2016arelistedinChapter9:TechnologyTransferActivitiesConcludingRemarksEarthquakesarenotpredictableandwedonotknowwhatthefutureholds,therefore,itisnotpossibletoknowwhetherwearegoingtoseeanincreaseoradecreasein2017orbe-yond.The2016decreaseinearthquakesofamagnitude4.0andgreaterdecreasestheprobabilitythatwecouldhaveadamagingearthquakeinOklahoma.Ontheotherhand,theoccurrenceofthreeearthquakesofmagnitude5.0andgreatersuggestscontinuing

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strongconcernaboutthepossibilityofdamagingearthquakes.BecauseitisimportantforOklahomanstounderstandhowtoprepareandwhattododuringanearthquake,ourweb-sitehasrelatedinformationandlinksaimedtoeducatethepublicaboutearthquakepreparedness.AcknowledgementsWewouldliketothankallthosethathelpedwiththemonumentaltaskofearthquakeanal-ysisin2015and2016,includingStephenMarsh,JenniferMorris,NoorulanGhouse,An-drewThiel,andJunjunHu.WewouldalsoliketothankIsaacWoelfel,ourseismologytech-nician,whomaintainstheseismographsandhasworkedtirelesslytoinstallnewandmoveexistingseismometersduringtheseverychallengingyears.WealsowishtoacknowledgeHarleyBenz,PaulEarle,DavidKetchum,JustinRubinstein,RobertWilliamsandmanyoth-ersattheUSGSfortheirhelp,supportandproductiveinteractions.ReferencesCitedAbercrombie,R.E.,1995,Earthquakesourcescalingrelationshipsfrom-1to5MLusingseismogramsrecordedat2.5kmdepth:J.Geophys.Res,v.100,no.B12,p.24,015-024,036.Aki,M.,1965,MaximumlikelihoodestimateofbintheformulalogN=a-bManditsconfi-dencelimits:Bull.EarthquakeRes.Inst.,TokyoUniv.,v.43,p.237-239.Brune,J.N.,1970,TectonicStressandtheSpectraofSeismicShearWavesfromEarth-quakes:J.Geophys.Res,v.75,no.26,p.4997-5009.Caprio,M.,Lancieri,M.,Cua,G.B.,Zollo,A.,andWiemer,S.,2011,Anevolutionaryapproachtoreal-timemomentmagnitudeestimationviainversionofdisplacementspectra:Geophys.Res.Let.,v.38,no.L02301,p.7.CEUS-SSC,2012,TechnicalReport:CentralandEasternUnitedStatesSeismicSourceChar-acterizationforNuclearFacilities,EPRI,PaloAlto,CA,U.S.DOE,andU.S.NRC,p.3176.Chen,C.,andHolland,A.A.,2014,APure-PythonPhasePickerandEventAssociator:Seis-mol.Res.Lett.,v.85,no.2,p.414.Darold,A.,Holland,A.A.,Chen,C.,andYoungblood,A.,2014,PreliminaryAnalysisofSeis-micityNearEagleton1-29,CarterCounty,July2014:Okla.Geol.Surv.Open-FileReport,v.OF2-2014,p.17.Gutenberg,B.,andRichter,C.F.,1944,FrequencyofEarthquakesinCalifornia:Bull.Seis-mol.Soc.Am.,v.34,no.4,p.185-188.Hainzl,S.,Scherbaum,F.,andBeauval,C.,2006,EstimatingBackgroundActivityBasedonInterevent-TimeDistribution:Bull.Seismol.Soc.Am.,v.96,no.1,p.313-320.Hanks,T.C.,andKanamori,H.,1979,AMomentMagnitudeScale:J.Geophys.Res.,v.84,no.5,p.2348-2350.Hardebeck,J.L.,andShearer,P.M.,2002,ANewMethodforDeterminingFirst-MotionFo-calMechanisms:Bull.Seismol.Soc.Amer.,v.92,no.6,p.2264-2276.

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Havskov,J.,andOttemoller,L.,1999,SeisAnEarthquakeAnalysisSoftware:Seismol.Res.Lett.,v.70,p.532-534.Holland,A.A.,2013,OptimalFaultOrientationswithinOklahoma:Seismol.Res.Lett.,v.84,no.5,p.876-890.Kanamori,H.,andAnderson,D.L.,1975,Theoreticalbasisofsomeempiricalrelationsinseismology:Bull.Seismol.Soc.Amer.,v.65,p.1073-1095.Miao,Q.,andLangston,C.A.,2007,EmpiricalDistanceAttenuationandtheLocal-Magni-tudeScalefortheCentralUnitedStates:Bull.Seismol.Soc.Amer.,v.97,no.6,p.2137-2151.Ottemoller,L.,andHavskov,J.,2003,MomentMagnitudeDeterminationforLocalandRe-gionalEarthquakesBasedonSourceSpectra:Bull.Seismol.Soc.Am.,v.93,no.1,p.203-214.Reasenberg,P.,andOppenheimer,D.,1985,Fpfit,fpplot,andfppage:Fortrancomputerprogramsforcalculatinganddisplayingearthquakefaultplanesolutions.:U.S.Geol.SurveyOpen-FileReport,v.85-739,p.25.Snoke,J.A.,Munsey,J.W.,Teague,A.G.,andBollinger,G.A.,1984,AprogramforfocalmechanismdeterminationbycombineduseofpolarityandSV-Pamplituderatiodata:EarthquakeNotes,v.55,p.15.Waldhauser,F.,andEllsworth,W.L.,2000,Adouble-differenceearthquakelocationalgo-rithm:MethodandapplicationtothenorthernHaywardfault:Bull.Seismol.Soc.Amer.,v.90,p.1353-1368.Zoback,M.L.,1992,First-andSecond-OrderPatternsofStressintheLithosphere:TheWorldStressMapProject:J.Geophys.Res,v.97,no.B8,p.11,703-711,728.

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DescriptionofRPSEATask6–CollectGravityInfillData:TheSubcontractorshallcollectadditionalgravitydatatoinfillexistinggravitydata.Thelocationoftheinfillgravitydatashallbedependentonthespatialresolutionoftheexistinggravitydataandthenecessitytovalidatethedensitydistributionwithinthe3Dgeologyinterpretationaspartoftherecursiveprocessaddressingthemisfitbetweentheobservedandestimatedgravitydata.

ThereportappendedbelowsummarizesgravitydatacollectionactivitiessupportedbytheRPSEAProject.

3. GravityDataCollectionStephenHolloway,KevinCrainOklahomaGeologicalSurvey,SarkeysEnergyCenter,Rm.N-131100EastBoydSt.,Norman,Oklahoma73019-0628

Introduction

ThegoalofthegravitycollectionportionoftheRPSEAprojectwassupplydatatomodelthesubsurfacestructuretobetterunderstandthestructureofthecrystallinebasementaspartofourefforttostudytheseismicityintheregion.TheobjectivesofthegravitycollectionfieldworkconductedfromJune2014toJuly2016wereseveral-fold:

• tocollectmoredenselyspacedgroundgravitymeasurementstoaddtoaregionalgravitydatabase,

• toidentifysignificantgravityanomaliestobeincorporatedintoageologicmodel,and

• toidentifyfaultsanddeeperstructuresespeciallyinareasofpossibleinducedseismicity.

ThisgravityfieldworkbuildsuponthePACESGravityDatabasedevelopedbytheUniver-sityofTexasatElPaso,whichcontainscontributionsfromtheU.S.GeologicalSurvey,theNationalGeospatial-IntelligenceAgency,NationalOceanicandAtmosphericAdministra-tion,industryandacademiccolleagues.DetailsofthePACESGravityDatabasecompilationeffortareavailableintheUSGSOpen-FileReport02-463(http://pubs.usgs.gov/of/2002/0463/).Ourworkfocusedonincreasingthespatialden-sityofthegravitymeasurementsinthedefinedRPSEAstudyarea,whichcenteredonthePragueearthquakesequence.Also,astheearthquakefrequencyincreasedandthelocationofseismicitychangedovertime,weshiftedourfocusnorthward,extendingbeyondouroriginalstudyarea.Gravitypotentialfieldanomaliesreflectvariationsinthephysicalpropertiesofrocksatdepth.Combinedwithindependentconstraintsfromgeologicfieldmapping,boreholeanalysis,geomagneticsurveyanomalies,andothergeophysicalobservations,gravitystud-iesprovideinsightintotheburiedgeologicalstructuresandthetectonicdevelopmentofthearea.

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GlobalPositioningSystem(GPS)Data

High-qualityGPSlocationdataarerequiredforaccurategravityanalysis.Sub-decimeterelevationaccuracyisneededtoobtaingravityreadingsthataremoreaccuratethan20mi-crogal(µGal,10-8m/sec2).Horizontalaccuracyisnotascrucialasverticalaccuracyinthegravitydatareductionprocess,althoughGPSsolutionstypicallyprovideahorizontalaccu-racythatisaboutthreetimesasfineastheverticalaccuracy.BoththeaccuracyandtheprecisionofaGPSsolutionareimportantforevaluatingthequalityofalocationdetermina-tion,butGPSprocessingsoftwarecommonlyreportsonlyprecisionestimates.WeemployedtwoGPSunits(abaseandarover)tomeasurehigh-qualitylocationsatgravitystations.Theseunitsutilizedual-frequencycarrier-phaseantennasandapplydif-ferentialcorrectionsrelativetolocalbasestationsaftertheGPStime-seriesarerecorded.TheGPSunitsusedwereTopconGB-1000receiverswithPG-A1withgroundplaneanten-nas.Topcondocumentationspecifiesahorizontalaccuracyof10mm+1.0ppm(xbaselinelength)andverticalaccuracyof15mm+1.0ppm(xbaselinelength).So,forexample,abaselineof10kmbetweenthebaseandroverGPSunitswouldyieldahorizontalaccuracyof20mmandverticalaccuracyof25mmunderidealconditions.Tofurtherincreaseouraccuracy,thebasestationmeasurementsaresubmittedtotheNa-tionalGeodeticSurvey's(NGS)OnlinePositioningUserService(OPUS),whichusesthethreenearestContinuouslyOperatingReferenceStations(CORS)intheregiontocalculatedifferentiallyahigh-precisionlocationofthebasestation.ThebaseandroverreceiversrecordedGPSdataevery5seconds.TheGPSroverdatawereacquiredatgravitystationsduring5-minuteoccupations.Onsomeoccasions,welostcar-rierphase-lockontheroverandhadtoreacquireit.Thisnecessitatesanew10-minutestaticwaittimebeforecontinuing.Wealsotestedreal-timekinematic(RTK)observationmodeinpriorfieldsessionsbutex-periencedproblemswithradioshadowing,outofrangeconditions,significantbatterydraw,plustheaddedcomplicationofneedingtomovethebasestationsmultipletimesperday.Weultimatelydecidedthatpost-processingwouldgiveussatisfactoryresultswhileutilizingourtimeefficientlyinthefield.GPSobservationsarerecordedasellipsoidalheightandmustbeconvertedtoorthometricheightbeforebeingusedforgeophysicalanalysis.WefirstconvertthestandardGPSout-putofWGS84datumtoNAD83(2011)toincorporatetheCORSstationcorrections.WethenconvertellipsoidalheighttoorthometricheightusingNAVD88(computedusingGE-OID12B).GravityDataWecollectedgravityobservationsat3,092locationsinnorthcentralOklahomaover160fielddaysfromJune2014toJuly2016(Figure3.1).Weusedtwogravitymeters,bothScin-trexCG-5Autogravsystems(serialnumbers080940457and080940101).Thesegravitymeterscomputeagravityreadingfromafilteredtimeseriesofrawreadingsoveraspeci-fiedintervaloftime.Weusedanoccupationtimeof1minute,whichwasrecommendedby

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themanufacturer.Ateachgravitystation,wecollected3occupationsandwhensubse-quentgravityreadingswerewithin0.02µGal,weacceptedtheaverageofthethreeread-ingsasthevalueforthestation.WeutilizedtheabsolutegravitybasestationSEC1thatwasestablishedin2005.SEC1islocatedinthebasementoftheSarkeysEnergyCenteronTheUniversityofOklahomacam-pus.Itisasmallbrasscapembeddedinconcreteoppositethetowerelevatorsonlevel1.AbsoluteghasbeenestimatedatSEC1tobe979656.483±0.016mGals.WevisitedSEC1atthebeginningandendofeachgravityfieldday,takingthreesetsofthreereadingsandthentakingtheaveragetoestablishourstartingandendingabsolutevalues.Aftertakingourabsolutegravitybasestationreadings,wethenwoulddrivetoapredeter-minedareaandestablishalocalrelativegravityfieldbasestation.Thislocationofthefieldbasestationwaschosenbasedonseveralfactorsincludingaccessibility,security,andacentrallocationforthedesiredareatargetedforthatfieldday.Goodpracticeistorepeatreadingsatthesamefieldbasestationovermultipledaysandtiethosereadingstotheab-solutegravitybasestation.Thisservesasanaddedcheckontherepeatabilityofreadings.Gravityobservationsweremadeadjacenttothefieldvehicle(Figure3.2)alongpublicroadways,generallyalongsection-lineroads.Stationswerelocatedwith2-milespacingasacompromisebetweencoverageanddensitybothtofillexistinggravitycoveragegapsandtocollectagridofhigherspatialdensitystationspacing.Toprocessthegravitydata,wefirstcorrectforinstrumentdriftbycomparingthediffer-encebetweenthetide-correctedgravityreadingsatthegravitybasestationatthebegin-ningandendingofeachday.Thisisinadditiontothebuilt-intidalandinstrumentdriftcorrections.Wethenapplythestandardlatitudecorrectionandfree-aircorrectiontoeachreading.Atthispoint,theFreeAirgravityanomalyvaluescouldbeincorporatedintoourgravitymodelingeffort.Atotalof9,020uniquegravityreadingswerereduced,resultingin3,092gravitystationswithaccompanyingpost-processedGPScoordinates.

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Figure3.1:GravitystationcoveragemapfortheRPSEAprojectarea(highlightedinred).Gravitystationscollectedforthisprojectareshowsasgreendots.GravitystationsfromthePACESgravitydatabaseareshownasblackdots.

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Figure3.2:ScintrexCG-5gravitymeterpreparedfortakingareadingatagravitystation.TheGPSroverantennaislocatedontheroofsecuredbyamagneticmount.

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DescriptionofRPSEATask9–ConstructionofIntegratedMulti-Variate3DGeologicInter-pretation

Thistaskprovidesthecrucialintegrativeplatformfortheintegratedanalysis.Amulti-vari-ate3-dimensional(3D)earthmodelbasedona3Dgeologicalinterpretationinitiallyem-ployingsubsurfacedata,digitalelevation,andresultsthatdefinestructuresbelowdrillingdepthsshallbedeveloped.The3Dinterpretationshallbebasedongravitydatathatcoversthestudyareauniformly,andshallbeiteratedbasedonresultssuchasseismictomogra-phy,seismicdataprovidedbyindustry,anddetailedwellloganalysis.

ThereportappendedbelowsummarizesaportionofTask9comprisingaseismictomographystudyinOklahoma,supportedbytheRPSEAProject.

4. SeismicTomographyofNorthCentralOklahomaChenChenOklahomaGeologicalSurvey,SarkeysEnergyCenter,Rm.N-131100EastBoydSt.,Norman,Oklahoma73019-0628

ThelargenumberofearthquakesthatoccurredinOklahomaandthesurroundingregionhavedrawnagreatdealofattentionsince2009.Manyseismometersweredeployedinthisregiontobetterrecordtheseismicity;thesenewinstrumentseasilyproducelargedatasetsthatarealmostimpossibletoprocessmanually.ChenandHolland[2016]developedaPy-thonpackageforautomaticallydetectingearthquakesandmakingphasepicks.ThesurgingseismicactivityinOklahomaprovidesanexcellentopportunitytostudydeepstructureswithinthecrystallinebasement,whicharehelpfultobetterunderstandtherelationshipbetweentheseismicityandgeologicalstructures.Priorto2009,earthquakesinOklahomaoccurredoverabroadregion,withoutshowingaclearrelationshipwithpreviouslyknownstructures.However,therecentprofoundseismicityincreasemayberelatedtoreactiva-tionoffaultsand/orfractureswithinthebasement,whichhavebeeninterpretedtobetrig-geredbywastewaterinjectionthatincreasesthepore-pressure,inturnpromotingfaultslip(forexample,Keranenetal.,2013).

Chenderivedtwovelocitymodelsusingnorth-centralOklahomaearthquakes.ByusingFMTOMO,hecreatedthefirstvelocitymodelwith>8000earthquakesofmagnitude2.0orgreater(M2+).Thismodelusedseveralcutoffs,suchasrequiringdepths>3.0km,numberofstationswithobservedarrivals>12,androotmeansquare(RMS)residualsoftravel-time<0.6seconds(s),thatwereselectedtocontrolthedataqualityandcomputationtime.Tobettercontrolthevelocitymodelfromthetomographicinversion,Chenfilteredthepickswithtravel-timeerrorsgreaterthan1.5scomparingtopredictedtravel-timebasedonaonedimensional(1D)velocitymodel.Afterfilteringthepicks,therewere153,119P-and145,949S-picksleft.TheVp/Vsratiousedwas1.73.

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ThereliableregionofbothP-andS-wavetomographyresultswasestimatedwithchecker-boardtests.Thealternativelyperturbedvelocityanomalieswereimposedontotheinitial1Dvelocitymodeltocreateacheckerboardpattern.Positiveandnegativeanomaliesof0.6km/s,wereaddedtoP-wavevelocity,andsimilarly±0.3km/swereaddedtoS-waveveloc-ityalternatively.Themodelwasparameterizedwithanoptimizednodespacingofabout0.15°(Dx:~13km)´0.12°(Dy:~13km)´2.8km(Dz)afterseveraltestswithdifferentnodespacing.Thesolutionconvergedwell,andtheresidualswerereducedtoareasonablelevelafter4iterations.ThecheckerboardpatternsoftheP-wavevelocitymodelshallowerthan~15kmwererecoveredforcentralandnorthcentralOklahoma.

ThesecondvelocitymodelwascreatedbyusingtheSIMUL2000packagewiththecompo-siteeventmethod,whichreducesthevolumeofthedatatoimprovethecomputationtime.Althoughthetotalnumberofpicksisreduced,thecompositeeventmethodpreservesasmuchoftheoriginalphasepickinformationaspossible.Inaddition,thismethodmakesthecompositeeventdistributionmoreuniform.8,194M2+eventswereusedtostartthistom-ographicprocessing.

Thefirsttargetearthquakewasselectedthatcontainsthemostpicksfromthe1Dvelocity-relocateddata.Acloseeventsearchalgorithmidentifiedthenearbyearthquakeswithinacertainradius(2kminourcase)centeredatthetargetevent.Foracertainstation,themedianvalueofallthepicksfromtheeventswithinthe2-kmsearchingradius(includingthetargetevent)wasselectedinsteadoftakingthemeanvalue.Themedianvaluewasassignedtothetargeteventasthephaserecordfromthatcertainstation.Alargerradiussearching(5kminourcase)followedtoexcludetheeventsbetweentwospheres(withra-dius2kmand5kminthiscase,respectively)forcandidatetreatmentofthenexttargeteventinthefuture.Therewere493compositeeventswith13,447P-picksand11,293S-picksconstructedfrom8,194M2+events.Thefirst485compositeeventswereusedtoconductthesecondvelocitymodelingstudy,whichhasmorethan99.5%ofthepicksfromallthecompositeevents.

A30-kmhorizontalgridwaschosentoinvertforthethree-dimensional(3D)velocitymodel,whichisabouttwicethegridsizeoftheFMTOMOmodel,duetothecomputationcapabilityrestriction.Theverticalgridpointsarenotequallyspaced,whichpermitsbetterrepresentationinourinitialvelocitymodel.TheVp-andVp/Vs-ratio-dampingparameterswereoptimizedwithaseriesofsingle-iterationinversions,respectively.FortheVpdampingdetermination,thedampingparametersrangedfrom50to2000toplotthedatamisfitsversusmodelvariationtradeoffcurve,whileprohibitingtheVp/Vsratioinversion.FromtheVptradeoffcurve,300waschosenastheoptimizedvaluebecausethedatamis-fitscanbereducedsignificantlywithoutintroducingtoomuchmodelvariance.ByholdingtheVpdampingfixedat300,ChencoulduseaseriesofVp/Vsratiodampingparametersfrom10to1000todeterminetheoptimizedvalueas70.Thus,300and70werechosenasthevaluesforVpandVp/Vsratio,respectively,inthetomographicinversions.Althoughlowerdampingvaluescanreducethedatamisfits,theycanintroducesomesharpandstrongvelocityanomalyfeaturesthatprobablyareartifacts.

Tobetterunderstandthestructuresinthecrystallinebasement,velocitymodels,gravity,andmagneticdatawereusedtoexaminethegeologicalcorrelation.Onalargescale,thevelocitymodelcorrelatestogravityanomaliesbecausedenserocksgenerallyhavehigh

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velocities,andviceversa.ThevelocitymodelsrevealstronglateralheterogeneitieswithinthePrecambriancrystallinebasement,whichindicatescomplexstructuresintheupperportionofthecrustinthestudyarea,suchasigneousintrusionsrelatedtotheOCM(OsageCountyMicrogranite),theSGG(SpavinawGraniteGroup),andthewidelydistributedCOGGCentralOklahomaGraniteGroup)unitinnorthcentralOklahoma(Reference).IestimatedalowVp/Vsratiozoneroughlyfromdepth~3–10km.Theaveragedbasementtopis~3kminOklahoma.Therefore,theVp/Vsratiocanbesimplifiedtothreelayers:<3km,~3to10km,and>10km,althoughthereisastrongvariationofVp/Vsratioinsomecross-sec-tions.Duetothecomplexfaultandfracturestructuresinthebasement,itisconsideredhighlypossiblethatwastewatercanpenetratetothedeepbasement,possiblyevendownto10kmormore.Water-filledfracturescanbeusedtoexplainthelowVp/VsratiozoneintheupperbasementofcentralOklahoma.

Earthquakelocationestimationisoneofthemostimportantinverseproblemsinseismol-ogy.Mostearthquakelocationmethodsarebasedonexploitingphasearrivalsfromtheseismicwaveformsandaselectedvelocitymodel.Accurateearthquakelocationisim-portantformanyapplications,suchasfaultstudies,hazardassessment,seismictomogra-phy,stressfielddetermination,identificationofinducedseismicity,andothers.

MostoftheearthquakesincentralOklahomaareclusteredandpresentednortheast-south-west(NE-SW)ornorthwest-southeast(NW-SE)trendingorientationthatisconsistentwiththe~East-Westmaximumhorizontalstressstatewithintheregion(Hollandetal.earth-quakesummary).Withthe3Dvelocitymodel,thecatalogedearthquakeswererelocated.Thehigh-accuracyearthquakelocationsimprovedtheresolutionoffaultlocationsbypro-ducingsharperpatternsofseismicity.Furthermore,theimprovedtheearthquakeloca-tionscanpotentiallybetterexplaintherelationshipbetweeninjectionwellsandinducedseismicity.Inaddition,theimprovementoftheearthquakelocationscanhelpidentifypri-maryfaultplanesfromfocalmechanisms,crustaldeformation,andothers.

The3Dvelocityrelocationstrategyistofirstrelocatethecataloguedearthquakeswiththesingleeventmethod,whichisusedtoimprovetheabsoluteearthquakelocations.Then,adoubledifferential(DD)methodfollowstoimprovetherelativelocationsfortheclusterednearbyeventswiththe3Dvelocitymodel.TheDDtechniquetakesadvantageofthefactthatifthehypocentralseparationbetweenthenearbyeventsismuchsmallerthantheevent-stationdistanceandvelocityvariationscale,theraypathsfromtheeventtothecom-monstationaresimilar.Inthiscase,therelativelocationbetweennearbyeventscanbeimprovedbythedouble-differentialtravel-timesandthehypocentralseparation,eventhoughthetravel-timesarebiasedbythe3Dvelocitystructures.Tocomparethediffer-encebetweenthe1Dand3Drelocationresults,thecatalogedearthquakeswererelocatedwitha1Dvelocitymodel.Figure4.1showstherelocatedearthquakesusingthe1DDDmodel.

Althoughthe1Dandthe3Dvelocityrelocationsshowsimilarshapesandorientationsofclusters,therearesystematicshiftsbetweentheresults.TwolargeearthquakegroupsthatareseparatedbyNemahaUplifthavedifferentdirectionsofshift.TheearthquakesareshowninFigure4.2.Mostoftheclustersinthesoutherngroup,whichisbetweentheNemahaFaultZone(NFZ)andtheWilzettaFaultZone(WFZ),basicallyshiftwestwardandnorthwestward(ingreenishcolor).Theclustersinthenortherngrouptothewestofthe

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NFZmainlyshiftsouthward(inreddishcolor).Thedominantshiftdistanceisabout0.5km,andtheaverageshiftamountis0.7km.Morethan80%oftheearthquakesshiftlessthan1km.Thereareonlyafeweventsshiftinggreaterthan2km.

DDmethodrelocationresultswiththe1DvelocitymodelAlthoughthe3Dvelocitymodelcanimprovetheabsoluteearthquakelocationsandrelativelocations,theDDrelocationwiththe1Dvelocitymodelstillhasimportantmeaningforthisstudy.TherelocatedearthquakesareshowninFigure4.1,whichalsopresentclearandnarrowclusters.Theshapesandorientationsoftheclustersarealmostallconsistentwiththe3Dvelocityrelocatedones.

After12relocationiterations,theRMStraveltimeresidualsreducedtoabout0.29s(Figure4.3(a)),whichisslightlyhigherthanthatofthe3Dvelocityrelocation.TheslightlyhigherRMSresidualswithmoreiterationnumbersmayindicatethatthe3Dvelocitymodelhasthebetterrelocationperformance.Figure4.3(b)showsahistogramoftheresidualsfrom

Figure4.1.Mapviewoftherelocatedearthquakes(dots)with1DDDmethod.Graypolygonsarethecounty boundaries. The black lines are the preliminary Oklahoma faults (Holland, 2015). NFZ:NemahaFaultZone;WFZ:WilzettaFaultZone.

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3DDDrelocationresults.Figure4.3(c)showsmostearthquakedepthsarearound5km.Aswiththe3Dvelocityrelocationresults,evaluationofhistogramsoflocationuncertain-tiessuggestthatmostoftheearthquakeshavesmalluncertainties,about0.4kmforxandydirectionsand0.6kmforzdirection.

Comparisonbetweenthe3Dand1DDDrelocationsAlthoughthe1Dandthe3Dvelocityrelocationsshowsimilarshapesandorientationsofclusters,therearesystematicshiftsbetweentheresults.Forcomparison,weplotteddif-

Figure 4.2. Epicentral shifts between the 1Dand 3D velocity DD relocation results. The coloredvectors(verysmallinthisscale)pointtothe3Dvelocityrelocatedearthquakesfromthesameeventsof1Dvelocity relocation. Color indicatesthe shiftazimuth.Eightsub-regions(A-H)are showninFigure6toexamineclustershiftinthesmallscale.Graypolygonsarethecountyboundaries.Theblack linesarethepreliminaryOklahomafaults(Holland,2015).NFZ:NemahaFaultZone;WFZ:WilzettaFaultZone.

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ferencesbetweenthe1Dandthe3DvelocityDDrelocationresultsinFigure4.2.Thevec-torspointtothe3DvelocityDDrelocationfromthe1DvelocityDDrelocationandarecolorcodedfordirectionsoftheshift.Twolargeearthquakegroupshavedifferentshiftingdirec-tions(Figure2).Asnotedabove,mostoftheclustersinthesoutherngroup,whichisbe-tweentheNFZandtheWFZ,basicallyshiftwestwardandnorthwestward(ingreenishcolor).TheclustersinthenortherngrouptothewestoftheNFZmainlyshiftsouthward(inreddishcolor).Figure4.4showsthehistogramoftheepicentralshiftdistancesbetweenthe1Dand3Dvelocityrelocationresults.Thedominantshiftdistanceisabout0.5km,andtheaverageshiftamountis0.7km.Morethan80%oftheearthquakesshiftlessthan1km.Thereareonlyafeweventswithshiftsgreaterthan2km.Figure4.5shows8sub-regions(blackdashedboxesinFig.4.2)toexamineclustershiftinginsmallscales.

Sub-regionAinFigure4.5(a)showstherelocatedclustersnearthetownofJones,OK.The3Dvelocityrelocatedearthquakes(dots)generallypresentasystematicshiftinorientationcomparedtothe1Dvelocityrelocation(vectortails).(Thesymbolsarethesameforallthesub-regionsinFigure4.5a-i.Thevectorspointtothe3DDDrelocationfromthe1DDDre-location.)Theprominentshiftindirectionsfortheearthquakesinthisareaisnorthwest,

Figure4.3:(a)ReductionoftheRMStravel-timeresidualwithiterationsforthe1DDDmethod.(b)Histogramsofresidualdistributionforinitialcatalogueddata(shaded)andrelocationdata(white).(c)Histogramofthedepthaftertherelocation.

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althoughthereareafewearthquakesmovinginotherdirections.Theclustersinthisaredonotseemtopresentclearorientations.

Sub-regionBinFigure4.5(b)showsthePraguesequence,whichisthelargestseismicse-quencethathasdrawnagreatdealofattention(e.g.Keranen,2013;McNamara,2015).Threemoderatedamagingearthquakes(Mw4.8,5.7,and4.8)occurredinearlyNovember2011nearPrague,OK.TheaftershockspresentaclearNE-SWtrendingorientationthatverylikelysuggestsarupture,andaninterpretedfaultwasinferredfromthissequence.Theearthquakesinthesequencetailshowmoreconsistentsouthwestshifting(inyellow-ishcolor).Thenorthwesternearthquakesinthesequenceshiftsouthward(inreddishcolor)tothefault,andthesoutheasternearthquakesinthesequenceprimarilyshiftnorthwestward(ingreenishcolor)tomakethesharperseismicitypattern.

Sub-regionCinFigure4.5(c)showsseveralclustersnearGuthrie,OK,whereaNE-SWtrendingfaultistothesoutheastoftheclusters.Mostoftheearthquakesshiftslightlytothewest(ingreenishcolor).Thelargestclusterinthisarea,withveryconsistentshifting,presentsaclearconjugate-planepattern(NE-SWandNW-SE).Theclusterinthesouthwestcornerappearstoshowtwoparallelseparatedsmallclusterswiththeprimarynorthwest

Figure 4.4. Histogram of the epicentral shift distances between the 1D and the 3D velocityrelocations.

34

shiftingandafewothershiftingdirections.Severalearthquakesatthenortheasterncornershifttothenortheast(inbluishcolor).

TherearetwoNE-SWtrendingclustersaroundCushing,OKinFigure4.5(d).Twoearth-quakeclustersinthissub-regionDpresentrelativelyconsistentnorthwestshiftingorienta-tions.Theearthquakesaroundthisregionhavetremendousmeaningtotheenergysecu-rityofUniteStates,whereoneoftheworld’slargestcrudeoilstoragefacilitiesislocated(McNamaraetal.,2015).InOctober2014,twoM4+earthquakesshooktheCushingoilhubthatisastrategicinfrastructureofUnitedStates.McNamaraetal.,(2015)inferredaWNW-ESEfaultbasedontheirearthquakerelocationstudy(Figure4.5e)forthesouthernclusterandmadeaseriesofanalyses.However,ourrelocationresultshowsNE-SWtrendingori-entationsforit,whichisdifferentthanMcNamaraetal.,(2015).Wethinkthatmorestud-iesmaybenecessaryforfurtherdetailstodemonstratethefaultstructuresinthisarea.

Sub-regionEinFigure4.5(f)isclosetothegapbetweentwolargeearthquakegroups.Mostearthquakesoftwoobviousclustersinthissub-regionshiftsouthwestward(inorangeandyellowishcolors).ThesetwoclustersalsopresentNE-SWandNW-SEorien-tations,whichareconsistentwiththemaximumhorizontalstressstateinOklahoma.Onlyafewearthquakesshifttootherdirections.

SeveralparallelNE-SWtrendingclustersinsub-regionF,southofMedford,areshowninFigure4.5(g).Thisareaislocatedinthelargenorthernearthquakegroup.Mostoftheearthquakesinthisareashiftsouthward(inreddishcolor).Theconsistentclusterorientationsmayindicatesimilarfaultstrikeorientationsinthissub-region.

Aswithsub-regionF,clustersinsub-regionG,northofMedford,alsopresentsystematicsouthwardshifting(inreddishcolor)inFigure4.5(h).SomeclustersshowNE-SWtrendingorientations,andsomeofthemshowNW-SEorientations,whichareclosetonearbyparallelfaultsegments.

Sub-regionHinFigure4.5(i)showsaNE-SWtrendingclusterontheGalenaTownshipFault,innorthwesternOklahoma.Theearthquakesinthisclusterprimarilyshifteastward(inpurplishcolor).Theclusteralignswellwiththemappedfaulttothesouthwest.Thisfaultmaybeblamedforthemostmoderateearthquakesinthiscluster,whichoccurredinearly2016.

DiscussionDemonstratingtherelationshipbetweentheearthquakesandgeologicalstructuresinOkla-homaisimportant,becausetheseismicityhasbeenveryactiveinthisregionsince2009.The3Dvelocitymodelcanimprovetheearthquakelocations,whichhelpstocorrelatetheseismicitywiththemappedfaults,interpretunmappedfaults,anddeterminetheconnec-tionbetweentheearthquakesandthewastewaterinjectionwells.Someoftherelocatedclusterspresentnarrowerandmorelineartrends,whichmayindicatethepotentialfaultsthatarerelatedtotheclusters.Therefore,thecorrelationbetweentheearthquakeloca-tionsandfaultsmaybeusedtodecidewheretobuildlarge-scalestructureswithlowrisk,suchashigh-risefacilities,oilstorageinfrastructures,pipelines,andothers.Inaddition,thecorrelationmayprovideinformationtoevaluateinsuranceratesofresidentialbuildingsinOklahomaaswell(LuzaandLawson,1982).

35

Figure4.5(b).Sub-regionBinFigure3(Praguearea).Epicentralshiftsbetweenthe1Dand3DvelocityDDrelocationresults(blackdots).Thecoloredvectorspointtothe3Dvelocityrelocatedearthquakesfromthesameeventsof1Dvelocityrelocation.Colorindicatestheshiftazimuth.ThethickblacklinesarethepreliminaryOklahomafaults(Holland,2015).Thegraylinesarethecountyboundaries.

Figure4.5(a).Sub-regionAinFigure3(Jonesarea). Epicentralshiftsbetweenthe1Dand3DvelocityDDrelocationresults(blackdots). The colored vectors point to the 3D velocity relocatedearthquakesfromthesameeventsof1Dvelocityrelocation.Colorindicates the shift azimuth. The thick black lines are thepreliminaryOklahomafaults(Holland,2015).Thegraylinesarethecountyboundaries.

36

Figure4.5(c).Sub-regionCinFigure3(Guthriearea).Epicentralshiftsbetweenthe1Dand3DvelocityDDrelocationresults(blackdots).Thecoloredvectorspointtothe3Dvelocityrelocatedearthquakesfromthesameeventsof1Dvelocityrelocation.Colorindicatestheshiftazimuth.ThethickblacklinesarethepreliminaryOklahomafaults(Holland,2015).

Figure4.5(d).Sub-regionDinFigure3(Cushingarea).Epicentralshiftsbetweenthe1Dand3DvelocityDDrelocationresults(blackdots).Thecoloredvectorspointtothe3Dvelocityrelocatedearthquakesfromthesameeventsof1Dvelocityrelocation.Colorindicatestheshiftazimuth.ThethickblacklinesarethepreliminaryOklahomafaults(Holland,2015).Thegraylinesarethecountyboundaries.

37

Figure4.5(e)SouthernclusterofearthquakesasrelocatedbyMcNamaraetal.(2015).TheirlocationstrendWNW-ENE,whereastherelocationsusingtherefinedvelocitystructureinthisreporttrendSW-NE.

Figure4.5(f).Sub-regionEinFigure3(Enidarea).Epicentralshiftsbetweenthe1Dand3DvelocityDDrelocationresults(blackdots).Thecoloredvectorspointtothe3Dvelocityrelocatedearth-quakesfromthesameeventsof1Dvelocityrelocation.Colorindi-catestheshiftazimuth.ThethickblacklinesarethepreliminaryOklahomafaults(Holland,2015).Thegraylinesarethecountyboundaries.

38

Figure4.5(g).Sub-regionFinFigure3(SMedfordarea).Epicentralshiftsbetweenthe1Dand3DvelocityDDrelocationresults(blackdots).Thecoloredvectorspointtothe3Dvelocityrelocatedearthquakesfromthesameeventsof1Dvelocityrelocation.Colorindicatestheshiftazimuth.ThethickblacklinesarethepreliminaryOklahomafaults(Holland,2015).Thegraylinesarethecountyboundaries.

Figure4.5(h).Sub-regionGinFigure3(NMedfordarea).Epicentralshiftsbetweenthe1Dand3DvelocityDDrelocationresults(blackdots).Thecoloredvectorspointtothe3Dvelocityrelocatedearthquakesfromthesameeventsof1Dvelocityrelocation.Colorindicatestheshiftazimuth.ThethickblacklinesarethepreliminaryOklahomafaults(Holland,2015).

39

Figure4.5(i).Sub-regionHinFigure3(GalenaTownshipFaultArea). Epicentral shifts between the 1D and 3D velocity DDrelocationresults(blackdots).Thecoloredvectorspointtothe3Dvelocity relocatedearthquakes fromthe sameeventsof1Dvelocityrelocation.Colorindicatestheshiftazimuth.ThethickblacklinesarethepreliminaryOklahomafaults(Holland,2015).Thegraylinesarethecountyboundaries.

40

MostoftheclusterspresentnarrowerlineartrendswithNE-SWorNW-SEorientationafter

the3Dvelocityrelocation,whichareconsistentwiththefavorablefaultorientationsincen-

tralOklahoma(Holland,2013).SeveralstudiessuggestthatrecentearthquakesinOkla-

homawerecausedbyreactivationofancientfaultsthatcutthroughtheArbuckleGroup

andextendintotheupperbasement(e.g.Holland,2013;AltandZoback,2014;McNamara

etal.,2015).(Holland,2013;Sumyetal.,2014;McNamaraetal.,2015)studiedthePrague

sequencewithavarietyoffocalmechanismdatatoshowthatmostoftheearthquakesin

thePraguesequencedisplaystrike-slipmotion,whichisconsistentwiththeknowledge

thatWilzettaFaultisaverticalornearverticalfault,atleastintheshallowsedimentary

sectionandupperbasement.However,notalltheclustershavebeenwellstudiedinOkla-

homa.Formanyrelocatedclusters,thereisnoidentifiedfaultnearby,butsomeoftheclus-

tersmayassociatewithlargegeologicalstructuresincentralOklahoma,giventhatthey

alignwellwithmappedfaults.Duetothestrongheterogeneityinthebasement,basement

faultsmaybecomplicatedthataredifficulttoassociatewiththeseismicityincrease.

ReferencesAlt,R.,andM.Zoback,2014,DevelopmentofadetailedstressmapofOklahomaforavoid-

anceofpotentiallyactivefaultswhensitingwastewaterinjectionwells,AGUFallMeeting

2014,abstract.

Holland,A.A.,2013,OptimalfaultorientationswithinOklahoma,Seismol.Res.Lett.,84,

876–890.

Holland,A.A.,2015,PreliminaryfaultmapofOklahoma,OklahomaGeol.Surv.OpenFile

Rep.,OF3-2015

Keranen,K.M.,H.M.Savage,G.A.Abers,andE.S.Cochran,2013,Potentiallyinduced

earthquakesinOklahoma,USA:Linksbetweenwastewaterinjectionandthe2011MW5.7

earthquakesequence,Geology,41,699-702,doi:10.1130/G34045.1.

Luza,K.V.,andJ.E.Lawson,1982,SeismicityandtectonicrelationshipsoftheNemaha

UpliftinOklahoma,partIV,OklahomaGeologicalSurveySpecialPublication,82-1.

McNamara,D.E.,H.M.Benz,R.B.Herrmann,E.A.Bergman,P.Earle,A.Holland,R.Baldwin,

andA.Gassner,2015,EarthquakehypocentersandfocalmechanismsincentralOklahoma

revealacomplexsystemofreactivatedsubsurfacestrike-slipfaulting,Geophys.Res.Lett.,

42,2742–2749,doi:10.1002/2014GL062730.McNamara,D.E.,G.P.Hayes,H.M.Benz,R.A.Williams,N.D.McMahon,R.C.Aster,A.Hol-

land,T.Sickbert,R.Herrmann,R.Briggs,G.Smoczyk,E.Bergman,andP.Earle,2015,Reac-

tivatedfaultingnearCushing,Oklahoma:Increasedpotentialforatriggeredearthquakein

anareaofUnitedStatesstrategicinfrastructure,Geophys.Res.Lett.,42,8328–8332,doi:10.1002/2015GL064669.

Sumy,D.F.,E.S.Cochran,K.M.Keranen,M.Wei,andG.A.Abers,2014,Observationsof

staticCoulombstresstriggeringoftheNovember2011M5.7Oklahomaearthquakese-

quence,J.Geophys.Res.SolidEarth,119,1904–1923,doi:10.1002/2013JB010612.

41

Zoback,M.L.,1992,First-andsecond-orderpatternsofstressinthelithosphere:The

worldstressmapproject,J.Geophys.Res.,97,11703–11728,doi:10.1029/92JB00132.

42

DescriptionofRPSEATask9–ConstructionofIntegratedMulti-Variate3DGeologicInter-pretation

Thistaskprovidesthecrucialintegrativeplatformfortheintegratedanalysis.Amulti-vari-

ate3-dimensional(3D)earthmodelbasedona3Dgeologicalinterpretationinitiallyem-

ployingsubsurfacedata,digitalelevation,andresultsthatdefinestructuresbelowdrilling

depthsshallbedeveloped.The3Dinterpretationshallbebasedongravitydatathatcovers

thestudyareauniformly,andshallbeiteratedbasedonresultssuchasseismictomogra-

phy,seismicdataprovidedbyindustry,anddetailedwellloganalysis.

ThereportappendedbelowdescribesaportionofTask9comprisingdevelopmentofathree-dimensionalmodeloftheProjectareaanditssurroundingsderivedfromgravitymeasure-mentsandgeologicalinformation,supportedbytheRPSEAProject.

5. GravimetricDeterminationofBasementGeologicStructure

KevinCrainOklahomaGeologicalSurvey,MewbourneCollegeofEarthandEnergy,UniversityofOkla-homa,NormanOK73019

Abstract

MostOklahomaearthquakesoccurwithinthecrystallinebasement.Thisstudyinvestigates

whetherwecanidentifycrystallinebasementgeologicstructuresthatmayconcentrate

seismicity.Thepaperalsoseekstoidentifythedifferencesinbasementgeologiccharacter

thatdoanddonothostearthquakes.

Intheholisticview,gravitydatameasurethegravityfieldgeneratedbytheuniverse’s

uniquedensitydistributionatthetimeandlocationoftheobservation.Intherealworld

thisstudywillbeusingtheobservedfree-airgravitydata.Thestudyusesthefree-air

gravitybecauseitdoesnothaveanembeddedgeologicmodel,asisthecaseinthesimple

orcompleteBouguergravitymodel(Nettleton,1976).

Thegeologiccharacteroftheuppercrystallinebasementcanbeestimatedandtestedusing

ageologicallyandstatisticallyconstraineddensityinversionofthreedimensional(3D)

free-airgravitydataandageologicallyconsistent3Ddensitydistributionofknownandex-

pectedgeologicfeaturesaboveandbelowtheuppercrystallinebasement.Thegravitydata

arefourdimensional(4D)pointdatacollectedatuniquelocationsandtimesandreflectthe

Earth’suniquedensitydistributionatthetimeofobservation.Thegeologicmodelisacon-

tainerpopulatedwiththedensitydistributionofageologicallyconsistentexpectedmodel

Earth.Thedensityinversionestimatesthedensitydistributionthatminimizesthemisfit

betweentheobservedandestimatedfree-airgravitydata.Iftheresidualfree-airgravity

anomaly(RFAA),isconsistent,thentheestimateddensitydistributionmaybecorrectbutif

theRFAAisinconsistenttheresultsarenotcorrect.

Usingpublishedformationisopachmodels,a3Dgeologicmodelisbuiltthatisconsistent

withknownandexpectedgeologiccharacteristics.Asmoregeologicinformationbecomes

43

available,theexpectedgeologicformationmodelcanbeimprovedtoreflectthesedata

whilemaintainingconsistencywithboththeregionalandlocalgeologicmodel.

Thereforethe3Dgeologicmodelrepresentsthepublished3Dgeologicdataconstrainedby

observedandexpectedformationboundariesandrocktypes.Then,usingexpectedrock

typetodensityrelationships,ageologicallyconsistentexpected3Ddensitydistribution

modelcanbebuilt.Usingtheexpected3Ddensitydistributionmodel,theexpectedgravity

effectofthemodelateach3DgravitystationlocationiscalculatedwithSIGMA.SIGMAisa

newlydeveloped,efficient,andextremelyrapid3Dgravity,gravitygradiometrycalculation

algorithmatthe3Dgravitydatapointlocations(ChangandCrain,2015).

Thenwithageologicmodelandstatisticallyconstraineddensityinversion,theupdated

densitydistributionmodelestimatesadensitydistributionthatminimizesthemisfitbe-

tweentheobservedfree-airandestimatedfree-airgravitydata.Thedensityinversionisa

geologicallyandstatisticallyconstrainedlinearinversionwithgeologicandstatistical

constraints(Jackson,1979,TarantolaandValette,1982,Baker,1988,andCrain,2006).

TheresultingRFAAreflectsbasementgeologicmassdistributionsthatindicatecomplex

basementrocktypedistributionandgeologicstructuresthatareconsistentwiththe

availabledata,andshouldprovideinsightintothedistributionofearthquakes.

Introduction

Definitivelydeterminingthegeologicstructureofthebasementrequiresrockinhand.

Giventheexpenseofdrillingtothebasement,muchlesstothedepthsofearthquakes

withinthecrystallinebasement,andthelackofaccessibleseismicreflectionsurveys,

geophysicalmeasurementsremainthemostcosteffectivemethodstoinvestigatebasement

rockproperties.

Approximately25to30percentofthestateofOklahomahasexploration3Dseismicreflec-

tionsurveysandprobably90percentofOklahomahas2Dseismicsurveys.However,these

dataarenotavailablepublicly,andthisstudymustrelyonpublisheddatatobuildthe3D

geologicvolume.Therefore,thisstudymustrelyonpotentialfieldmethods,suchasmag-

neticandgravitymeasurementsavailablepublicly.

Ofthepotentialfieldmethods,themostcosteffectivegeophysicalmethodisaeromagnetic

dataandthatshouldbethefirstchoice.Butgiventhecosttoacquirenewhigh-resolution

aeromagneticsurveys,theOklahomaGeologicalSurveyhasusedlow-resolutionpublic

domainaeromagneticdata,(Bankey2002),andgravitydatafromthePanAmericanCenter

forEarth&EnvironmentalStudies[PACES],(Hinze2004),followedupwithnewlyacquired

gravitydata(Chapter3)toinvestigatetargetedanomalies.Fullyinvestigatingthegeologic

characterofthebasementusinggravimetricmethodsrequiresmorethanoneiterationof

expectedgeologicmodels.

Themodeleddomainmustbesubstantiallylargerthanthestudyareatoaccuratelyrepre-

sentthethree-dimensionaleffectsofrockmassesonthegravityfieldatagivenpoint.The

studyareaisshownasarectangleinthefiguresinthispaper.Themodeledareaincludes

muchofOklahoma,butalsopartsofadjacentKansas,Arkansas,andMissouri.TheProject

areanearthePragueearthquake,isshownasasmallerrectangle.Figure5.1showsamap

oftheobservedFreeAirAnomaly(FAA).

44

Figure5.1.Observedfree-airanomaly,FAAovernortheasternOklahoma,southeasternKansas,andwesternMissouriandArkansas,withexpectedbasementgeologicunits.TheFAAandbasementgeo-logicunitsdonotcorrelateverywellexceptintheMid-ContinentRift(MCR)andSouthernOklahomaAulacogen(SOA);RockunitYo(micro-graniteofOsageCounty)innorthernOklahomaisanindicatorofanigneousintrusion,butitselfisnotthesourceoftheOsageCountyanomalysourroundingit,be-causethereisnodensitycontrastinthebasementrocks.

Usinginterpretedthreedimensional(3D)geologicmodels,thisstudycalculatesthemodel

free-airanomalyatthelocationsoftheobservedfree-airgravitydatausingtheexpected

modeldensitydistribution.Thenapplyingageologicallyandstatisticallyconstrainedden-

sityinversion,theestimateddensitymodelminimizesthemisfitbetweentheobserved

(Figure5.1)andestimated(Figure5.2)free-airgravitypatterns.Theresidualfree-air

anomaly,RFAA(Figure5.3)representstheextenttowhichunmodeled,unknown,or

mismodeledgeologicfeaturescausethemodeltodifferfromtheobservations.

MCR

SOA

Yo

45

TheRFAAinFigure5.3illustratesthecomplexityofthebasementgeologybetweenthe

mid-continentrift,MCRinKansas,andtheSouthernOklahomaAulacogen,SOA.

Associatedwiththetworifts,MCR,andSOA,areparallelgeologicstructureslikethe

NemahaUpliftandAmarilloUpliftandtheAnadarkobasin.Also,thereareadditional

associatedstructuresthroughoutOklahomaliketheWilzettaFaultzoneandtheirmany

conjugatefaultzones.

TheanomaliesintheRFAAshowcomplexandpreviouslyun-mappedlong-livedstructures

withexpectedtectonicimplications.SpecificallyinFigure5.3,attheKansas–Oklahoma

Border,atthesouthernendoftheMCR,thereappeartobetwobranchesofgravityhighs

Figure5.2.Estimatedfree-airanomalyoverthesameregionasinFigure1istheresultofthedensityinversionestimatingthemodeldensitiesthatminimizethemisfitbetweentheobservedandestimatedfree-airgravity.

MCR

SOA

Yo

46

(red)whichpreviouslyareunmappedandhaveearthquakeactivityinorverynearthem.

Therefore,giventhecomplexityofthebasementstructures,weshouldinvestigatethegeo-

logicfeaturesnotonlyduetotheearthquakesbuttheinfluenceofthebasementgeology

eveninareaswithoutearthquakes.

GeologicandGravityModel

AspreviouslystatedtheEARTH’sgravityfieldresultsfromtheuniquedensity

distributionoftheUniverseincludingthesun,moon,andplanets,commonlylumpedinto

the“tides”correctionandtheEARTH’sgeologicstructure.Theobservedgravitydataare

pointmeasurementsoftheEarth’scontinuousgravityfieldmeasuredatdiscretepoint

locations.Forthisstudy,weassumeastaticdensitydistributiontomodeltheobserved

Figure 5.3. Regional basement geologic map laid over residual Free-Air Anomaly, RFAA, thedifferencebetweenFigures1and2.Rectangleshowsprimaryprojectarea.

47

gravityfieldattheirdiscretedatalocationsusingageologicallyconsistent3Dgeologic

model,withknownandexpectedrockdensitydistributionsandtheiruncertainties.

Theobservedfree-airgravityatanylocationmeasuresthegravityeffectofthedensitydis-

tributionofgeologicfeatures.Theinitialphaseofinterpretingtheobservedfree-airgravity

isremovingthegravityeffectsofknownandexpectedregional3Dgeologicunits.Thenthe

RFAArepresentsthegravityeffectoftheunmodeled,mismodeled,orunexpecteddensity

distributionswithintheuppercrustmodelthatiscurrentlyusingageologicallyconsistent

uniformsingledensity.

TheRFAAisthedifferencebetweentheobservedfree-airanomalyandtheestimatedfree-

airanomalycalculatedusingestimatedmodeldensitiesreturnedbyageologicallyandsta-

tisticallyconstraineddensityinversionthatminimizesthemisfitbetweentheobservedand

estimatedfree-airanomaly.

ModelingtheRFAArequiresdensitydistributionsconsistentwithexpectedandassumed

geologicfeaturestheyrepresent.Usingageologicandstatisticallyconstraineddensityin-

versiontominimizethemisfitbetweentheresidualgravityandtheestimatedresidual

gravityallowsprogressiverefinementofthedocumentablegeologicalmodel.Iftheresults

arestatisticallyconsistent,thentheresultingmodelmaybecorrect,butanyinconsistent

resultsaredefinitelyincorrect.

Theinitialphaseoftheinterpretationistoimagethegravityeffectoftheunknowndensity

distributionwithintheuppercrust.Theinitialmodeliscomposedoffourindividualgeo-

logicmodelsfromthesurfacetopographyto100kmbelowmeansealevel(BMSL),as

showninFigure5.4.Degreeofdetaildecreaseswithdepth,reflectingthelackofavailable

dataregardingthedeeperlevelsofthecrustandmantle.Eachelementofthegeologic

modelshasgeologicandstatisticalconstraintsusedbythedensityinversionwhen

estimatingthedensitiesthatminimizethemisfitbetweenthepriorandposteriormodeldensities.Thefirstmodelunitcomprisesthesedimentaryrocksabovethecrystalline

basement.Thesecondmodelunitistheuppercrust.Thethirdmodelunitisthelower

crust.Thefourthmodelunitisthemantle.

Figure5.5showsthenearsurfacesedimentaryrockabovethecrystallinebasement.The

currentsedimentaryrockmodelisauniformdensityvolumeattheaveragedensityofthe

sediment.Theexpectedvolumeisdefinedbytwosurfaces.Thetopsurfaceisthesurface

topographyatonearc-secondresolution(~30mgridspacing),andthebottomsurface,

thecrystallinebasement,isdefinedbya30arc-secondgridtopography(~1kmgrid).The

mostprominentfeaturesofthesedimentarysectionarethethicksectionsintheArkoma

andAnadarkoBasinsinthesouthernmarginoftheblock.Inaddition,theNemahaFault

showsupasaridgerunningroughlynorth-souththroughthemiddleoftheblock.

Theuppercrustbeneaththesedimentarysectionistherockvolumeofinterestbecauseit

ishostingmostOklahomaearthquakes.ThisunitisshowninFigure5.6.Theinitialmodel

assumestherockintheuppercrustisgranitic,withaconstantdensity,andanydensity

variationswithintheuppercrustshouldshowupasanomaliesintheRFAA.Theexpected

volumeisdefinedbytwosurfaces.Theuppersurfaceisthebasementsurfacebelowthe

sedimentarycolumn.Thebottomsurfaceisat25kilometersBMSL.

48

Thedeepcrustmodel,Figure5.7,isanestimateddensitydistributionusing0.10-degree

squareprismsextendingfrom25kmto42kmBMSL.Individualcelldensitiesareesti-

matedrockdensitiesbetween2.9to3.0g/cm3appropriateforthedepthof25to42km

BMSLandreturnedbythedensityinversionminimizingthemisfitbetweentheobserved

andestimatedFAAs.Theexpecteddeepcrustgeologicmodel,below16kmBMSL,reflects

ageologicallyconstraineddensitydistributionconsistentwithexpectedandacceptedgeo-

logicfeatures,boundaries,anddepths.

Themantlemodel,Figure5.8,isamulti-densitymodelextendingfrom42kmto100km

BMSL.EachdensityprismisthenearestneighborareawiththeEarthScopetransportable

arraystationinthecenterandthedensityreturnedbythedensityinversion.Theexpected

densityofthemantlewassetto3.3g/cm3andthedensityuncertaintysetto±3%.

Figure5.9showstheRFAAwithgeologicboundaries,andillustratesthecomplexityofthe

geologicarchitectureassumedtooccurintheuppercrust.Therearedistinctdifferencesin

thegeologicinterpretationbetweenKansasandOklahoma.Kansasusedaeromagnetics

anddrillholesamplestohelpdefinetheirgeologicmodel,whereasOklahomadefinedthe

Figure5.3.3Dgeologicmodelunitsfromthesurfacetopographyto100kmbelowsealevel.

49

basementgeologysolelyonthebasisofoutcropanddrillholesamples.Thelackofdatahas

leftlargeareasofOklahomawithnodatadefiningthegeologicunits.

Withincreasedearthquakeactivityinthecrystallinebasement/uppercrust;onemayask

aretheregeologicstructuresinthebasementthatreflectearthquakeseismicity?Figure

5.10showstheRFAAandmagneticintensity,alongwiththeirfirstverticalderivative.The

firstverticalderivativecommonlyshowstheedgesofgeologicstructuresifthereisarock

typedifferenceorpossiblyanelevationoffsetintherock.Themajorityofthecurrent

faultsarestrike-slipfaults,andthereforethereareareaswithoutdistinctsignaturesinthe

firstverticalderivativemaps.Anadditionalproblemisthespatialresolutionofthedata.

InmostofthestateofOklahomaboththegravityandmagneticdataspacingareatthescale

oftheearthquakeclustersorlarger.

FutureworkImprovingtheaccuracyofthedensitymodelrequiresintegratingadditionalgeologic

formationandstructuraldata.Wecurrentlyhavelimitedaccesstomorecomprehensive

data,thoughifitbecomesavailable,theregional3Dgeologicmodelcanbeupdated

integratingthesedataintotheregionalmodel.Theabilitytoupdatethegeologicmodelsin

Figure5.4.Surfacetopographytobasementtopography.

50

apiecewisemannerallowsimprovingthegeologicmodelwheneverdatabecomesavailable

whilemaintainingmodelconsistencyatallgeologicmodelscales.

Asecondimprovementofthesedimentarymodelwouldintegratewell-logdensitydata

intothemodelformationvolumes.Anadditionalimprovementwouldbewiththeaidof

industrydatatolocallyupdatetheregionalgeologicmodelswithdetailedseismicandwell-

logformationtopsandformationdensitydata.Anotherimprovementwouldbetouse2D

seismicdepthsectionsand3Dseismicvolumestoimprovetheformationtopsand

basementtopography.

Futureinvestigationstargetinglocalgravity/magneticanomaliesshouldtargetlocal

geologicfeaturesandrequireacquiringadditionalhigh-resolutiongravitydataalongwith

updatingtheregionalgeologicmodel.Eachnewtargetedlocalgeologicmodelwill

specificallyaddressgravityanomaliesrevealedintheregionalRFAAandcombined,they

wouldimprovetheoverallunderstandingofthegeologicstructureandtheobservedfree-

airgravityanomaly,whilemaintaininggeologicmodelconsistencyatbothregionaland

localscales.

Figure5.5.Uppercrustfrombasementtopographyto16kmBMSL.

51

Inthefuture,removingthegravityeffectoftheregionalsedimentarygeologicmodelunit

shoulduse3Dgeologicvolumesandtheirexpecteddensitiesconvertedfromtheir

expectedrocktypes.Wearecurrentlyworkingonupdatingthesedimentarymodelusing

isopachmapsfromTulsaGeologicalSocietySpecialPublication3(RascoeandHyne,1988),

producingamulti-layergeologicvolumewithexpectedandvolumetricallyconsistentrock

densitydistributions.Anyadditionalformationtopelevationsandrockdensitiescan

integrateintotheregionalgeologicmodelwithindividualupdatesmaintaininggeologic

consistencyoftheregionalgeologymodel.Initially,theregionalformationtopsandnew

updatedaverageformationdensitieswillupdatethegeologydensitydistributionmodel.

Figure5.10showsthatthereareareaswithinOklahomawhereearthquakesshowcorrela-

tionwiththegravityandmagneticanomalies.Additionally,inFigures5.10,largescale,and

5.11,smallscale,thereareapparentgeologicstructuresinOklahomawithoutearthquake

activity.

Figure5.11illustratesthedataaliasingprobleminWoodwardandWoodscounties.The

currentgravitydata,whitedots,wherethedataspacingissimilartothatofmuchofthe

Figure5.6.Deepcrustmulti-densitymodelfrom25kmto42kmBMSL.

52

gravitydatainOklahomaandtheinter-stationspacingissimilartothecurrentearthquake

clusterspacinginthesecounties.TheWoodwardandGalenaTownshipearthquakeclus-

tersareonthescaleof14to16km,andthegravitydataspacingis10to14km.Boththe

RFAAandmagneticdataandtheirfirstverticalderivativesshowindicationsofgeologic

structurewithintheregionoftheearthquakeclusters.However,makingdefinitive

statementsaboutgeologicstructureisimpossibleduetodataaliasing.

Conclusion

Theresidualgravityanomalyalignswithpreviouslyknowngeologicfeaturesinthe

basementinareasoftheSouthernMid-ContinentRiftandSouthernOklahomaAulacogen.

Also,thebasementgeologicstructuresarecommonlycoincidentwithknownand

previouslyunknownstructuresinthebasementrevealedbyearthquakeactivity.

Theresidualgravityanomalyandmagneticdatacommonlyindicatemanyoftheareasof

earthquakeactivityhavebasementstructureassociatedwiththem.Theresidualgravity

anomalyandmagneticmapsshowthestructureforalargevolume.Atthesametime,there

areearthquakeclustersthatappeartobeinternaltobasementgeologicunitswithout

Figure5.7.Mantledensitymodelfrom42kmto100kmBMSL.

53

apparentinternalstructure.Thereareatleastthreepossibleexplanationsforthis

phenomenon.

1. Partofthebasementhasauniformrocktypewithoutgeophysicalexpressionofneworexistingfaulting.

2. Twodifferentbasementrockunitshavingthesamedensityorsusceptibilityoccuracrossafaultorstructure,therefore,obscuringthechangeingeologicunits,and

3. Thespatialresolutionofthegravityandmagneticdataarealiasingthegeologystructureandobscuringthegeophysicalsignatureofthegeology.

Figure5.8.RFAAwithgeologicunitboundariesusing"traditional"colorscaleusedforgravitydata

54

Therearealsoplaceswheretheresidualgravityanomalyhintsatgeologicstructurebut

doesnotseemtobeabletoresolvethestructure;thisismoreoftentheresultofaliased

signalduetosparsedataundersamplingthegravityandmagneticsignal.Theonlysolution

toaliaseddataistoacquirehigherresolutiongeologicalandgeophysicaldata.

Usingthe3Ddataandmodelformatallowsupdatingthedata,andgeologicmodelina

piecewisewayasnewgeologicalandgeophysicaldatabecomeavailable.Thepiecewise

modelingphilosophyisvaluablefortestingmultiplehypothesesforthebasementgeologic

unitsandstructures.Thisapproachalsofacilitatedintegrationofresultsofmultiple

studiesintothemodeltoimprovetheunderstandingofthebasement,anditsimpactto

Oklahoma.

WithinOklahoma,thereisastatewideneedtoacquirenewhigh-resolutiongravityand

magneticdatatoimprovethespatialresolvabilityofthefeaturesfoundintheresidual

gravity.TheWoodwardandWoodsCountyearthquakeclusterareasclearlyillustratethe

needtoacquirenewhigh-resolutiongravity,magneticandgeologicdataalongwith

improvedgeologicmodelsofthesedimentaryformationsandstructuresabovethe

crystallinebasement.Acquiringnewgeophysicalandgeologicaldatacanimprovethe

imagingofthebasementgeologicstructureassociatedwiththefaultsdelineatedbythe

earthquakesandatthesametime,enhancetheunderstandingofthebasementgeologic

featuresinareasthathavedistinctivegeologiccharacteristics,butdonothostearthquakes.

References

AmericanAssociationofPetroleumGeologists(AAPG)andtheUnitedStatesGeological

Survey(USGS),BasementRockProjectCommittee,1967,BasementMapofNorthAmerica,

BetweenLatitudes24°and60°N,1:5,000,000.

Baker,M.R.,1988,Quantitativeinterpretationofgeologicalandgeophysicalwelldata:

DoctoralDissertation,Univ.ofTexasatElPaso.

Bankey,V.,Cuevas,A.,Daniels,D.,Finn,C.,Hernandez,I.,Hill,P.,Kucks,R.,Miles,W.,

Pilkington,M.,Roberts,C.,Roest,W.,Rystrom,V.,Shearer,S.,Snyder,S.,Sweeney,R.E.,

Velez,J.,Phillips,J.D.,Ravat,D.K.A.,2002,Digitaldatagridsforthemagneticanomalymap

ofNorthAmerica,USGSPublicationsWarehouse,

http://pubs.er.usgs.gov/publication/ofr02414

Blakely,R.J.,1996,PotentialTheoryinGravityandMagneticApplications,Cambridge

UniversityPress,461p.

Chang,J.C.,andCrain,K.,2015,GravityModelingwithVerticalLineElements,AGU

PotentialFieldsWorkshop,Keystone,Colorado,August2015

Crain,K.,2006,ThreeDimensionalGravityInversionwithaPrioriandStatisticalConstraints:DoctoralDissertation,Univ.ofTexasatElPaso.

55

Figure 5.9. Earthquake epicenters with geologic boundaries, over public domain gravity andmagnetic data. Left side, RFAA, and RFAA first verticalderivative.Rightside,magneticsurvey,andmagneticfirstverticalderivative.Thereddotsareearthquakesmagnitude4andlarger.

56

Figure5.10.WoodwardandWoodscountiesearthquakeepicentersovergravityandmagnetic.Leftside,RFAA,andRFAAfirstverticalderivative.Rightside,magnetic,andmagneticsfirstverticalderivative,leftsideandmagneticsandfirstverticalderivative.Thereddotsareearthquakesofmagnitude4andlarger.

57

Danes,Z.F.1960,OnaSuccessiveApproximationMethodforInterpretingGravity

Anomalies,Geophysics,25,1215-1228.doi:10.1190/1.1438809

Denison,R.E.,andMerritt,C.A.,1964,BasementRocksandStructuralEvolutionof

SouthernOklahoma,OklahomaGeologicalSurvey,Bull.95,302p.

Denison,R.E.,1981,BasementRocksinNortheasternOklahoma,OklahomaGeological

Survey,Circular84,88p.

Dicken,C.L.,Pimley,S.G.,Cannon,W.F.,2001,Precambrianbasementmapofthenorth

Mid-Continent,U.S.A.,Adigitalrepresentationofthe1990P.K.Simsmap,U.S.Geological

Survey;Open-FileReport2001-21,pubs.er.usgs.gov/publication/ofr0121

Hammer,S.,1974,ApproximationingravityInterpretationCalculations,Geophysics,v39,

205-222.doi:10.1190/1.1440422

Hinze,W.,etal.,2005,Newstandardforreducinggravitydata:TheNorthAmericangravity

database,Geophysics,Vol.70,No.4,p.J25–J32.

Jackson,D.D.,1979,Theuseofaprioridatatoresolvenon-uniquenessinlinearinversion:

Geophys.J.R.Astron.Soc.,57,137-157.

Nettleton,L.L.,1976,GravityandMagneticsinOilProspecting,McGraw-HillPress.

Rascoe,B.,andHyne,N.,eds.PetroleumGeologyoftheMid-Continent,TulsaGeologicalSociety,SpecialPublicationnumber3,1988.

Tarantola,A.,Valette,B.,1982,Generalizednon-linearinverseproblemssolvedusingleast

squarescriterion:Rev.ofGeophys.AndSpacePhysics,20,219-232.

58

DescriptionofRPSEAProjectTask10–4DIntegratedMultiscaleReservoirandGeologicalModeling:Afield-scalemodelrepresentativeoftheOsageCountygravityanomaly(theref-erencemodel)shallbedevelopedusinganensembleofmodelsthatareprogressivelyup-

dated.Asetofpredictionsshallbegeneratedthroughcouplednumericalsimulationofwa-

termovementinthesubsurfaceandthelocalizedstresschangesassociatedwithwaterin-

jection.Thesepredictionsshallbecomparedtoobservationsofseismicactivityinthere-

gionthathavepreviouslybeenattributedtowaterdisposalandbyreconcilingthesediffer-

encesinthemodeltocreateanimprovedrepresentationofthepreferentialflowpaths,ge-

omechanicalpropertiesandfaultcharacteristicsinthesubsurface.Theimprovedmodel

shallbetestedagainst4Dgeophysicalmonitoringanalysesandfurtherrefined.Thisshall

directlyaddressthekeychallengesrelatedtoimprovedquantification,sensitivityandres-

olutionofmonitoringtechnologies.Bysequentiallycalibratingreservoirperformance

modelstoallavailablemonitoringdata,improvedpredictionanddelineationofthein-

jectedwaterbecomespossible.

Thereportappendedbelowsummarizesthemathematicalbasisforevaluatingpressurere-sponseininjectionwells,aspartofthistasksupportedbytheRPSEAProject.

6. InterpretationofLowFrequencyPressureMeasurementsinInjectionand

ProductionWells

DeepakDevegowdaMewbourneCollegeofPetroleumandGeologicalEngineering,SarkeysEnergyCenter100EastBoydSt.,Norman,Oklahoma73019-0628

Theintentofthischapteristodelineateamathematicalprocedureforreservoircharac-

terizationandpressureresponseanalysistoidentifyhighlyconductivefluidmigration

pathwaysinthesubsurfacefrominjectionwellpumpingtests.Pumpingtestsonproduced

waterdisposalwellsareanecessaryfirststeptoidentifyfluidmigrationpathwaysinthe

vicinityoftheinjectionwell.Thesefluidmigrationpathwaysmayincludefractures,inter-

sectingfaultsorhighpermeabilityzones.Inthiswork,wedocumentalowfrequencyas-

ymptoticapproachbasedonVascoandKarasaki(2006)tointerpretthesepumpingtests.

6.1SubsurfaceCharacterizationfromDynamicData

Theeconomicimpactofinaccuratepredictionsoffuturepetroleumreservoirperformance

issubstantial.Thereforemakingpropercharacterizationofthereservoiranduncertainty

analysesinproductionforecastsarecrucialaspectsinanyreservoirdevelopmentstrategy.

Thisgoalisequallyapplicabletoproducedwaterdisposalwellsatvariousdisposalsites.

Accuratecharacterizationofthesubsurfaceiscriticaltopredictingtheultimatefateofthe

injectedwateranditspotentialtoinduceseismicity.Thisgoalisachievedthroughtheuse

ofhistorymatchingalgorithmswhichreconcilereservoir/subsurfacemodelstomeasure-

mentssuchaspressureorinjection/productiondataortimelapseseismicinformation.

Theworkflowdependsonconstructinganappropriateinitialsubsurfacesimulationmodel

andadjustingthevaluesoftheuncertainmodelvariablessothatthemodelperformanceis

inreasonableagreementwithactualmeasurements.Theseapproachescanbebroadly

59

classifiedintotwodistinctcategories:gradientbasedalgorithmsandstochasticap-

proaches.Regardlessoftheapproach,allpreviouslyrecordeddataissimultaneouslyused

toupdatethereservoirmodel.Thefirstclassofalgorithmsgenerallyutilizesparameter

sensitivitiesorgradientsofanappropriatelyconstructedobjectivefunctiontoarriveata

solutiontotheinverseproblem.Togeneratemultiplehistorymatchedmodelrealizations,

thesetechniquesinvolvetherepeatedapplicationoftheproceduretoeachrealizationof

thereservoir,aprocedurewhichcanbecomputationallydemanding.Furthermore,these

approachesrelyonthedevelopmentofcodethatmaynotbecapableofhandlingdiverse

typesofdynamicdata.

Ontheotherhand,stochasticalgorithmsliketheMarkovChainMonteCarlo(MCMC)ap-

proach,simulatedannealingandgeneticalgorithmsrelyonstatisticalapproachestoarrive

atsolutionstotheinverseproblem.However,theseapproachesareslowtoconvergeand

requireexcessiveturn-aroundtimesformodelcalibration.Theassociateddifficultieswith

bothcategoriesofhistorymatchingalgorithmsarefurthercompoundedwhenitisneces-

sarytoassimilatedatafrequently.

Becauseoftheincreaseddeploymentofpermanentsensorsordownholemonitors,itisin-

creasinglyimportanttomaintain‘livemodels’thatareprogressivelyupdatedassoonas

dataisobtained.Inanycase,thereisastrongneedtoseeksolutionsthatprovidereasona-

blyaccuratesolutionsinacomputationallyfeasibleframework.Inthiswork,wedescribe

anapproachdevelopedbyVascoandKarasaki(2006)thatreliesonalowfrequencyap-

proximationofthepressurediffusivityequationthatcanaddressthechallengesassociated

withnoisypressuremeasurementsacquiredduringapumpingtesttocharacterizehigh

conductivityfluidmigrationpathwaysinthesubsurface.

6.2Methodology

VascoandKarasaki(2006)haveinvestigatedanasymptoticsolutionoflowfrequencytran-

sientpressurevariationstoestimatehydraulicfractureconductivity.Theinversionofhy-

draulicfracturetomographycanbeusedtoestimatepermeability.In2000,Vascoandhis

colleaguesinvestigatedthehighfrequencyasymptoticsolutionforpressurevariationequa-

tions.Theseequationsproposesolutionsfortransientpressureamplitudeandarrivaltime

throughtheuseofdiffusivetraveltimetomography.Theuseofthisapproachisconducted

throughapplyingconstantrateteststhatarerunforspecificperiodsoftime.Theusesof

thesetestsaregovernedbyutilizingthetimederivativetoestimatearrivaltime.Compu-

tingthetimederivativeisusuallytroublesomeduetoregionalandwelleffectsthatcause

initialtimevariations.

Thismethodisusuallysurroundedbygreatnumberofdataandnoiseaccompanyingdata

acquisition.Therefore,thelowfrequencyasymptoticapproachusesthefrequencydomain

toreducetheamountofdataneededtofindsolutions.Usingboththeforwardandthein-

versesolutionsrequireonlytwoproblems,whichareexpressedbythesteadystatepres-

sureequations.

Thisstudyfocusesonusingthelowfrequencyapproximationtothediffusivityequation

becauseofthefollowingassumptions:

60

1. Thehighfrequencyvariationsaresensitivetonoiseinthemeasurements.2. Thelowfrequencyresponsescorrespondtolateralandverticalvariationsinthe

reservoirproperties.

3. Workinginthefrequencydomainreducesthenumberofobservationsneededsignificantly.

4. Themethodiseasilygeneralizedandcanbeappliedtomanydifferentreservoirandtestingscenarios.

6.3ThePressureDiffusivityEquation

Thefollowingequationdefinesthefinalformofpressurevariations" #, % :

∇ '() ∙ ∇" + '()∇ ∙ ∇" = - ./.) (1)

Wheretheterm(())denotesthetotalmobilitydefinedas

() =0123141

+ 0523545

(2)

Totalmobilitydoesnotvarysignificantlywithposition,x;thusitwillbetreatedasacon-

stant.ThetermC(x,t)orcoefficient(C)doesnotvarywithtime,t,duetothesaturation

constraint(67 + 68 = 1)mentionedabove.Thecoefficient,Cisgivenby:

- = :;:<+ =>767 + =>868 (3)

6.4TheLowFrequencyAsymptoticSolution

Inthisstudy,thelow-frequencyasymptoticsolutiontothediffusivityequationshownin

Equation1isemployedtoquantify,interpret,andinvertpressurevariationsinthelowfre-

quencydomain.Alow-frequencyapproachisadoptedinthisworkbecauseseveralofthe

high-frequencyvariationsinpressuremaybebecauseofchangesinwelloperatingcondi-

tionsorresponsestolocalizedchangesinreservoir/aquiferproperties.Lowfrequency

variationsontheotherhandarelikelytoberespondingtoalargerscalereservoir/injec-

tionvolumesurroundingtheinjectionwell.Transformingthepressurepressuretothe

frequencydomainalsoreducesthevolumeofobservationdatatoamuchsmallersetofob-

servationsandeliminatesnoiseinthemeasurementsofpressure.

Oneessentialpartoftheasymptoticinverseproblemtechniquearethesensitivitycalcula-

tions.Thesecalculationsarerequiredtostudyreservoirparametervariationsandtheir

consequenteffectondependentreservoirparameters.Fundamentally,implementingdif-

ferentmethodsofsensitivitycalculationsprovidesadditionalauthenticationofthepro-

posedapproachandverificationofitsvalidity.Sensitivitycalculationsarediscussedlater

inthechapter.

Themainpurposeoftheasymptoticapproachistofindasolutionforthediffusivepressure

componentthatemulatesthecharacteristicsofthewavepropagationmodel.Many,includ-

ingVirieuxetal.(1994),havestudiedtheasymptoticapproachinderivingthediffusivity

equationinthefrequencydomain.Thefollowingnotationdescribesthegeneralformof

61

thesolutiontothediffusionequationinthefrequencydomain.Theuseofthisequationis

discussedlaterinthechapter.

" #,? =w x,ω CD EFG H

I (4)

Virieuxetal.(1994)explainsthatthediffusionequationwhentransformeddependsonthe

expressionexp( ?).Asimilarfactorexp(?N/P)appearedintheasymptoticsolutionofwavepropagationmodeloftheHilbertTransform.AsaresultofVirieuxetal.(1994)ob-

servations,thediffusionequationinthefrequencydomainwasdefinedinthatspecific

form.

Theasymptoticsolutionfortheequationdescribingthediffusivecomponent,pressure,is

transformedtothefrequencydomainusingaFouriertransformintegraldescribedinEqua-

tion5.WorkinginthelowfrequencyorlongperioddomainrequirestransformingP(x,t),

pressurevariationsasafunctionoflocation,x,andtime,t,to"(x,?).Theterm"(x,?)isdefinedasthepressurevariationinthefrequencydomainasafunctionoflocation,xand

frequency,?.

" #,? = QRSI)" #, % T%UVRV (5)

Todescribethebehaviorofpressurevariationsinthefrequencydomain,thepressureis

transformedthroughaFastFouriertransform.Asaresult,thepressureequationshownin

Equation1inthefrequencydomainbecomes:

∇ '() ∙ ∇" + '()∇ ∙ ∇" = ?-" (6)

ThepermeabilityisrepresentedbythetermK(x)andthepressurevariationsinthefre-

quencydomainisdefinedbytheterm".Pressurevariationscanalsobedescribedinthefrequencydomainthroughpowerseriesrepresentations:

" #,? = CD FG H

I "7(#)V

7WX ?7 (7)

ThefunctionY # isdefinedasthephaseand(n=0,1,2…).Thisformofthepressureequationisadoptedfromtherepresentationofthediffusivityequationinthefrequency

domaininahomogeneousmediumforanimpulsivesource(Virieuxetal.,1994).Thistype

ofequationisdominatedbythefirstfewtermsforwhenthemagnitudeofthefrequency,?issmall.Thesolutionofthepressureequationinuniformmediaisdescribedbysomeform

ofamodifiedBesselfunctionofthezerothorder'X( ?Z[).ThetermZisaconstantdependingonmediumpropertiesandristhedistancefromthesource.Thesolutionof

Equation6isanadaptationofthemodifiedBesselfunctionforsmallfrequency,?(VascoandKarasaki,2006).Thesolutiontothepressurevariationandthediffusionequationin

thefrequencydomainis:

" #,? =w x,ω CD FG H

I (8)

Theexpressionw x,ω dependsontheordersofthefrequencymagnitudesandisdefined

byitsseriesformas:

w x,ω = "7 #V7WX ?7 (9)

62

ThepressurevariationterminEquation9,"7(#),isafunctionoflocation,x.Notethat,toworkinthelowfrequencydomain,onlythesmallestmagnitudesoffrequencywhere(? ≪1)wereused.Therefore,therepresentationofthepressure" #,? inEquation8issignifi-

cantlycontrolledbythefirstfewterms.Accordingly,thefinalformofEquation6canbe

usedtoadequatelyrepresentthepressurevariationsinthelowfrequencydomain.Thisis

showninEquation9wheretheterm"X(x)isdefinedasthezeroth-orderamplitudeofthepressurevariations.

" #,? = CD FG H

I"X(#) (10)

Tousetheequationabovetocalculatethelowfrequencypressurevariationsforagiven

model,theterms"X(#)andY # needtobecalculated.ByusingtheexpressionsgivenaboveinEquation5,weobtainanewsetoftermscharacterizedbydifferentordersoffre-

quency, ?.Themathematicaloperationsconductedaresummarizedbelow.Theterms(∇)and(∇ ∙ ∇)arespatialderivativesthataredefinedasthegradientandtheLaplacianexpres-sions,respectively.Astep-by-stepdetailedmathematicalformulationofthesolutioncan

befoundinVascoandKarasaki(2006).ThegradientandtheLaplacianrespectivelyare

givenby:

∇" #,? = CD FG H

I ∇w x,ω − ?∇Y # w x,ω (11)

∇ ∙ ∇" #, ? = CD FG H

I w x,ω ?∇Y # ∇Y # − ?∇ ∙ ∇Y # w x,ω −

2 ?∇Y # ∇w x,ω + ∇ ∙ ∇_ #, ? (12)

SubstitutingEquations11and12for∇" #,? and∇ ∙ ∇" #, ? intoEquation6generates

thefollowingequation:

' # () w x, ω ω∇Y # ∇Y # −∇ ∙ ∇Y # w x,ω − 2∇Y # ∇w x,ω +

?RN `∇. ∇_ #, ? + ∇' # () ?RN `∇w x,ω −∇Y # w x,ω = ω- # w x,ω (13)

ThegeneratedequationaboverepresentsthefinalformofEquation6aftersubstitution,

factoringouttheexponentterm,anddividingbothsidesbytheterm ?.Substitutingtheexpressionforw x,ω definedinEquation10,wegetasumofinfinitenumberofexpres-

sionswithvaryingordersoffrequencies ?.Letusrecallthatweareaimingtoworkinthelowfrequencydomain.Therefore,onlyfrequencies( ?)ofsmallmagnitudesareconsid-ered.

Thesolutiontoderivinganequationofpressurevariationsinthelowfrequencydomainis

donethroughexaminingthetermsofEquation13.Thetermscombinedwiththesmallest

ordersoftheterm ?,areselected.Thesolutionstotermswith ?Db, ?c

,and ?b

frequenciesarediscussedbelow.

63

Termsoforder dDe

Examiningtermswiththesmallestorder ?Dbprovidestheequationdefiningthezeroth-

orderamplitudeofthepressurevariations"X(x).' # ()∇ ∙ ∇"X x +∇[' # ()] ∙ ∇"X x = 0 (14)

Theexpressionaboveisafirstorderdifferentialequationthatresemblestheequationgov-

erningthestaticpressure.Notethatthesolutionofthezeroth-orderamplitude"X(x)equa-tiondependsonthetotalmobility()andthepermeability' # .Inaddition,Equation14isindependentoffrequency,thus,onlyonesolutionperwellpointisneeded.

Termsoforder di

Examiningtermswiththesecondsmallestorderoffrequency ?c,providesanequation

neededtosolveforthephasecoefficientσ # .K x ()"X x ∇ ∙ ∇σ # + ∇ ' # () ∙ "X x ∇σ # + 2K x ()∇"X x ∙ ∇σ # = 0 15)

Thisequationshowsthedependencycharacteristicsofthephasecoefficientonthezeroth-

orderamplitude"X(x),thetotalmobility() ,andthehydraulicpermeability' # .Tosolveforthephaseparameter,Equation13mustbesolvedfirst.Theequationabovecanbere-

writteninamorecompactformusingthecoefficientandtheirderivatives.

Ω # ∇ ∙ ∇σ # + m x ∙ ∇σ(x) = 0 (16)

WherethetermsΩ # andm x denotethescalarandvectorcoefficientsmentionedaboveandaregivenby:

Ω # = K x ()"X(x)m x = ∇ ' # () "X x + 2K x ()∇"X(x) (17)

Theequationsrequiredtosolveboththezeroth-orderamplitude"X(x)andphasecoeffi-cientσ(x)arebothindependentofthefrequency.Asaresultonlyonesolutionperwellisneededforeachparameter.

Termsoforder de

Examiningtermswiththelargestorderoffrequency ?b,providesanequationrelatingthe

zeroth-orderamplitude"X(x),thephasecoefficientσ # ,andtheamplitudeterm"N(#).∇ ∙ ' # () ∙ ∇"N = - # − K x ()∇σ ∙ ∇σ "X (18)

Solvingforamplitudeterm"N(#)requiressolutionsforbothEquations17and18.Equa-tion18isidenticaltotheequationofstaticpressure.Theonlydifferencesnotedarethe

deviationsofthephasecoefficientfromthediffusivetravel-time.Solutionofthediffusive

traveltimeinhighfrequencydomainisdescribedbytheeikonalequationrepresentedby

therightsideofEquation18.

Inordertoestimatethepressurevariationsinthefrequencydomain,boththezeroth-order

amplitudepressureandthephasecoefficientsmustbecalculatedusingEquations12and

64

15.Theequationsgoverning"X # andY # areindependentofthefrequencies,thereforeonlyonesolutionperwellneedstobecalculated.

6.5.ModelParametersSensitivityCalculations

Themainpurposeofthesensitivitycalculationsistorelatevariationsofaspecificmodel

parameteratpointytoobservationsrecordedatpointx.Inthisstudy,themodelparame-

tersarethepermeabilityvalueswithinthemodelateachgridlocationandtheobserva-

tionsarepressuremeasurementsrecordedatanobservationwellduringapumpingtest.

Inthisstudy,theperturbationsinhydraulicpermeabilitynop orno(q)locatedatpointyarerelatedtotheobservedvaluesofthederivativeofthepressuren" #, ? inthewelllo-

catedatpointx.Therearetwomethodsthatwereusedinthisstudy.Thelow-frequency

asymptoticapproachallowsustocalculatethesensitivitiesofchangesinpressureto

changesingridblockpermeabilityvaluessemi-analytically.Numericalsensitivitiesarealso

calculatedtodemonstratethevalidityofthesemi-analyticalsensitivity.Thesemi–analytic

sensitivitycalculationsarediscussedinthenextfewsections.

6.5.1Semi-AnalyticalSensitivityCalculations

Thesensitivitiesarecalculatedthroughthecomparisonofhydraulicpermeabilitiesatpoint

yalteredslightlyfrombaseorbackgroundpermeabilitywithvalue'r(q).Thesamemethodisusedtocomparechangescreatedatthepressureatpointxtoabackgroundor

basemodelthathasapressureof"r #, ? .Equations19and20definethecomparison

madebetweenthepermeabilitiesandpressurebeforeandafterperturbations:

n' q = 'r(q) − '(q) (19)

n" #, ? = "r #, ? − " #,? (20)

ThereaderisreferredtoVascoandKarasaki(2006)forfurtherdetailsofthesensitivity

computation.Thefinalexpressionforthesensitivityforasinglesource-wellisrelatedto

thesquareofthepressuregradientandisgivenby:

s< t,Is2 u

= −2∇"X #, q ∙ ∇"X #, q QR SIv u,t (21)

6.5.2ComparisonwithNumericalSensitivityCalculations

Thesemi-analyticsensitivitiesderivedinEquation21arenowcomparedwithnumerical

sensitivities.Notethatnumericalsensitivitiesarederivedbyperturbingeachgridcellper-

meabilityvaluebyasmallvalueandsolvingthefullfieldsimulationtoobtainchangesin

thepredictedbottomholepressureattheobservationwell.ThereforeifthereareNpa-

rametersinthemodel,computationofthenumericalsensitivitieswouldnecessitateN+1

fullsimulationruns.Thiscanrapidlybecomecomputationallyprohibitiveandunderscores

thesignificanceofsemi-analyticsensitivitycomputations.

65

Weconsideramodeldefinedona21x21x1gridwithaproducingwelllocatedinthecenter

ofthefieldinthemiddleofmesh(SeeFigure6.1).Theuniformpermeabilityofthereser-

voirformationis8.12millidarciesandtheuniformporosityis10%.Theboundarytothe

northofthefieldisaconstantpressureboundaryof2000psia.

Thenumericalsensitivitieswerecalculatedbyperturbingthepermeabilityofeachofthe

gridblocksby5%andre-computingthepressurevariationsattheobservationwell.This

processisrepeated441times,onceforeachgridblock.Finally,thenumericalsensitivities

canbecomputedoncethedifferencesinwellborepressureinthefrequencydomainare

knownforthecorrespondingchangesingridblockpermeability.Thetotaltimerequiredto

implementthismethodisapproximately40minutesofrunningtime.Figure6.2showsthe

semi-analyticsensitivitiesderivedusingEquation21.

Figure6.3showsthenumericalsensitivitiescalculatedforthesamemodel.Comparingthe

twomethodsused,itcanbenoticedthatthesensitivitiesshowninFigures6.2and6.3are

verysimilarandthereforeprovidevalidationfortheanalyticapproachtocomputesensi-

tivitiesviaEquation21.ThetotalcomputationtimeforthesensitivitiesinFigure6.2was4

seconds.

6.6ResultsandConclusions

Inconclusion,theuseoftheasymptoticlow-frequencyapproachtointerpretpressure

measurementsispromisingandallowsforrapidassessmentofsubsurfaceheterogeneities.

Figure6.1:Arrangementofthewells intheteststudy.Thenorthboundaryisaconstantpressureboundaryof2000psia.

66

Additionally,italsoprovidesamechanismbywhichnoisymeasurementsmaybefilteredto

useonlythosemeasurementswithmeaningfulinformationcontent.

Theapproachdescribedinthischapterallowsforahigh-resolutionreconstructionofcon-

ductivepathwaysinthesubsurfaceforfluidmigration.Consequently,intheabsenceof

Figure6.2: Semi-analytic sensitivities computed for thepressure recorded in theobservationwell inFigure1.

Figure6.3.NumericalsensitivitiesforthepressureobservationsintheobservationwellinFigure1.

67

othergeophysicalmeasurementsorgeologicinterpretation,itprovidesasoundapproach

toaddressingconcernsoverthemigrationofinjectedwateranditsroleininducedseismic-

ity.ThemethodologydescribedhereborrowsheavilyfromVascoandKarasaki(2006)but

isverypromisingtodeterminethefateofinjectedwaterinsaltwaterdisposaloperations.

6.7References1. Gradshteyn,I.S.,andI.M.Ryzhik.1980,TableofIntegrals,Series,andProducts,Else-

vier,NewYork.

2. Oliver,D.S.1993.Theinfluenceofnon-uniformtransmissivityandstorativityondraw-down.WaterResourcesResearch29(1):169–178.

http://dx.doi.org/10.1029/92WR02061.

3. Vasco,D.W.2000.Analgebraicformulationofgeophysicalinverseproblems.Geophysi-calJournalInternational142(30):970–990.http://dx.doi.org

/10.1046/j.1365-246x.2000.00188.x.

4. Vasco,D.W.2004.Estimationofflowpropertiesusingsurfacedeformationandpres-suredata:Atrajectory-basedapproach.WaterResourcesResearch40(10):1-14.

W10104.http://dx.doi.org/10.1029/2004WR003272.

5. Vasco,D.W.,andK.Karasaki.2001.Inversionofpressureobservations:Anintegralformulation.JournalofHydrology253(1–4):27–40.DOI:

http://dx.doi.org/10.1016/S0022-1694(01)00482-6.

6. Vasco,D.W.,andK.Karasaki.2006.Interpretationandinversionoflow-frequencypres-sureobservations.WaterResourcesResearch42(5)W05408.

http://dx.doi.org/10.1029/2005WR004445.

7. Vasco,D.W.,H.Keers,andK.Karasaki.2000.Estimationofreservoirpropertiesusingtransientpressuredata:Anasymptoticapproach.WaterResourcesResearch

36(12),3447–3465.http://dx.doi.org/10.1029/2000WR900179.

8. Vera,F.andEconomides,C.2014.DescribingShaleWellPerformanceUsingTransientWellAnalysis.SPEJournal10(2):24-28.SPE-0214-024-

TWA.http://dx.doi.org/10.2118/0214-024-TWA.

9. Virieux,J.,Flores-Luna,C.,andGibert,D.1994.Asymptotictheoryfordiffusiveelectromagneticimaging.GeophysicalJournalInternational119(3):857-868.

68

DescriptionofRPSEAProjectTask10–4DIntegratedMultiscaleReservoirandGeologicalModeling:Afield-scalemodelrepresentativeoftheOsageCountygravityanomaly(theref-erencemodel)shallbedevelopedusinganensembleofmodelsthatareprogressivelyup-

dated.Asetofpredictionsshallbegeneratedthroughcouplednumericalsimulationofwa-

termovementinthesubsurfaceandthelocalizedstresschangesassociatedwithwaterin-

jection.Thesepredictionsshallbecomparedtoobservationsofseismicactivityinthere-

gionthathavepreviouslybeenattributedtowaterdisposalandbyreconcilingthesediffer-

encesinthemodeltocreateanimprovedrepresentationofthepreferentialflowpaths,ge-

omechanicalpropertiesandfaultcharacteristicsinthesubsurface.Theimprovedmodel

shallbetestedagainst4Dgeophysicalmonitoringanalysesandfurtherrefined.Thisshall

directlyaddressthekeychallengesrelatedtoimprovedquantification,sensitivityandres-

olutionofmonitoringtechnologies.Bysequentiallycalibratingreservoirperformance

modelstoallavailablemonitoringdata,improvedpredictionanddelineationofthein-

jectedwaterbecomespossible.

ThereportappendedbelowsummarizesworkonmodelingofinducedseismicityunderpartofRPSEATask10,withreferencetoactivitiessupportedbytheRPSEAProject.

7. ModelingPorePressureVariationsandPotentialforInducedSeismicityAdjacent

toWaterDisposalWells.

DeepakDevegowdaMewbourneSchoolofPetroleumandGeologicalEngineering,MewbourneCollegeofEarthandEnergy,UniversityofOklahoma,NormanOK73019

Theobjectiveofthisstudyistodeduceatemporalandspatialcorrelationbetweensalt-wa-

terinjectionandearthquakefrequencyusingnumericalmodels.Studiesofseismicityin

thevicinityofsalt-waterdisposal(SWD)wellsoftenrelyonidentifyingstatisticalrelation-

shipsbetweenSWDwelllocation,injectedwatervolume,rateofinjectionandthetimingof

seismicity.Forinstance,byplottingwellheadpressuremeasurementandsaltwaterinjec-

tionratethroughtime(Figure7.1),theOklahomaGeologicalSurveyreportastrongtem-

poralandspatialcorrelationbetweensaltwaterdisposalwellsandoccurrenceofthe

earthquakeactivitythatisclearlydistinctfrombackgroundseismicityrate(DaroldA.P.et

al.2014)inOklahoma.Relativeproximityofinjectionsitestoearthquakeeventlocations

suggestsacloselinkbetweenthetwo;however,suchanalysesmayhavelimitedutilityfor

predictivepurposes.Forinstance,someofthekeyconcernsare:

• Isthereacriticalinjectionratebelowwhichseismicitymaybemanaged?

• Whatistheoptimaldistanceforinjectionwellsfromafault?

• Doesthefaulttransmissibilityplayaroleingoverninginducedseismicity?

Inthisstudy,weemploynumericalmodelingtoexplainhypocenterlocationsofinduced

seismicityinthePrecambrianbasementthatarelocatedmorethanakilometerbelowthe

injectionzoneandtoinvestigateporepressurediffusionthattriggersfaultslipinthecrys-

tallinebasementspecificallyinrelationtoeventsinOklahoma.

69

7.1LiteratureReview

WhereastherehasbeenalowlevelofbackgroundseismicityhistoricallyinOklahoma,

therehasbeenasharpincreaseinseismicityofabout300timessince2009inaportionof

thestate(Figure7.2).Ratesofsalt-waterdisposal(SWD)fromoilandgasoperationshave

beenincreasingsince2005,andin2013,aretentimesaslargeasthevolumesrecordedin

2000(Table7.1).Thisinturnhasraisedconcernsaboutthelinkbetweenoilandgasac-

tivityandseismicityintheregion.InOklahoma,producedwaterdisposedinasalineaqui-

ferthroughverticalSWDwellsextendtoatotaldepthof2.2kmtoabout3.5kmintheAr-

bucklegroup,withsomewellsterminatedadjacentto,orinthePrecambrianbasement.

Hypocenterdepthsoftheearthquakesunderamagnitudeof2.5MLin2014aremostlylo-

catedwithinthebrittleuppercrustatthedepthof~2to5kmintothecrystallinebase-

ment.WenowprovideabriefdescriptionoftheArbucklegroupandthebasementrele-

vanttothemodelingexercises.

Geology:TheArbucklegroupofcentral-southOklahomahasavariablethicknessof600to3500m,consistsdominantlyofinterbeddedthincarbonatemudstone,interclastcalcare-

nite,laminateddolomiteordolomiticlimestonewithfewlaterallyconsistentsandstone

beds(FritzD.Richardet.al.2013).TheArbuckleGrouphistoryhasincludedmultiple

phasesofdiagenesisandthereforesomeunitshaveacomplexporositynetworkcontrolled

bydiagenesis,depositionalenvironment,paleokarstformationwithfaultoverprints.Por-

osityoftheupperArbuckleGrouprangesashighas25%-65%(WilliamEHam,1973),alt-

houghmuchoftheGroupislessporous.BelowtheArbuckleisigneousbasementrockof

Precambrianagemadeupofrhyolitewithverylowporosity(10-15%)andpermeability

Figure.7.1:PlotshowingtemporalcorrelationbetweenthesaltwaterdisposalandearthquakedatafromCartercounty(DaroldA.P.etal2014)

70

(10-15-10-18m2)(Morganet.al.2015).Thethicknessofthiscrystallinebasementunit

rangesfromabout2600mtomoreto3500m.

Hydrogeology:TheArbuckleGroupconsistsinlargepartofaquiferqualityrock.Becauseofpoorqualityoftheaquiferwaterandduetothepresenceofstrongconfinementabove

theaquifer,lowporosity,permeabilityandgreatdepth,itiseconomicallyimpracticaltouse

thiswater.TheArbuckleGroupcanacceptalargeamountofwaterwithoutincreasing

wellheadpressure,althoughthecauseofthisunderpressureisstillpoorlyunderstood.

OneexplanationcouldbethatSWDwellcompletionintervalsincludekarstifiedsectionsor

fracturesthathavehigherpermeabilitythanthematrixpermeability,whichallowstheAr-

buckleSWDwellstobehaveasiftheywereunderpressuredinOklahoma(Morganet.al

2015).

StructuralDescriptionoftheArbuckle:ThesoutherncentralpartoftheArbucklegroupishighlyfaultedandfoldedwithmajorfaultorientationinthenorth-westdirection.Fig.7.3

&7.4showthepositionofSWDwellsandfaultswithoptimalorientation(thoselikelyto

haveanearthquake).Thefocalmechanismdistributionisdominatedbystrike-slipmotion

onsteeplydippingfaults.Optimalorientationoffaultsrangesbetween45°-60°,105°-120°

and135°-150°,andrepresentorientationsmostlikelytohaveanearthquake,giventhe

Figure.7.2:EarthquakesinOklahomareportedbyOGSin2014(OklahomaEarthquakeSummaryReport2014,OGSOpenfilereport-2015).ThegreatestnumberofearthquakeshaveoccurredinCentralandnorth-centralOklahomabutanincreaseisobservedinNortheastOklahomafrom2015.

Table7.1:SaltWaterDisposal(SWD)volumeinMbblperzoneZone 2009(Mbbl) 2010(Mbbl) 2011(Mbbl) 2012(Mbbl) 2013(Mbbl) 2014(Mbbl)

Arbuckle 434,230 449,406 525,027 566,047 842,631 1,046,913

Basement 1,368 771 621 1,379 820 2,162

71

roughlyEast-WeststressfieldinmuchofCentralOklahoma.Moderatelyoptimalorienta-

tionrangesbetween15°-45°,60°-75°,90°-105°and120°-135°andrepresentfaultorienta-

tionsmoderatelylikelytohaveanearthquake.Allotherorientationsoffaultstrikearesub-

optimalorientationandhavealowlikelihoodtohaveanearthquake(Murray2014,OGS

OF5-2015).Theseresultsdonotindicatethatearthquakescannotoccuronsub-optimal

faultstrikes,butsuggestthattheyarelesslikely(Murray2014,OGSOF5-2015).Fig.7.4

ShowsthatmajorfaultstrendsinnorthcentralOklahomadeducedfromfocalplanesolu-

tionsareforstrikeslipmotionsonsubverticalfaults(DaroldandHolland2015).

AbsoluteStressMagnitudeandCriticallyStressedCrust:Stressinthelithospherecanbedeterminedbytheearthquakefocalmechanism,whicharethemostubiquitousindicators

ofprincipalstressorientation.Mechanismsofstressdeterminationincludethepatternof

seismicwaveradiationfromthefocalpointoftheearthquake.Differenttypesofearth-

quakes(Strikeslip,NormalandReversefault)definethemagnitudeofverticalstress,maxi-

mumhorizontalstressandminimumhorizontalstress(ZobackandZoback,2002).Weare

usingasimplemodelofstressmagnitudevariationwithdepthwherethefaultisinastate

offrictionalequilibrium.Thisdescribesacriticallystressedcrustinwhichthedifferences

betweenfrictionalandshearstressesareveryclosetothevaluesrequiredforslipforopti-

mallyorientedpre-existingfaults(ZobackandZoback,2002).

7.2KnownMechanismsofFluidInjection-InducedSeismicity

Porepressurecanplayatwo-foldroleintheearthquakeprocessby:

1. Decreasingtheeffectivestressand/or2. Alteringtherockchemicallytoreducethecoefficientoffrictiononthefault.

Failurecriteriaforfrictionalslidinggovernthefrictionalstrengthofapreexistingfault.Be-

causeoffriction,acertainshearstressvaluemustbeachievedintherockbeforefrictional

slidingisinitiated,anddefiningthiscriticalstressisthefailurecriterionforfrictionalslid

ing(Byerlee’slaw).Wearetakingcohesionaszeroforpreexistingfaultedrock.

Figure.7.3:FaultorientationinOklahoma.(Murray2014)

72

Faultslippageoccurwhenshearforceonthefaultplaneisgreaterthanthefrictionalforce,

i.e.τ=So+μ*σe(where,τ=shearstress,So=cohesiveforce,whichiszeroincaseofpreex-

istingfaults.μ=cofficientoffaultfriction&σe=Effectivenormalstress).Effectivenormal

stress,σe=(σn-Pp),whereσn=LithostratigraphicnormalstressandPp=porepressure.An

increaseintheporepressureisaccompaniedbyanetdecreaseintheeffectivenormal

stressandthisshiftstheMohr’scircletotheleft.FailureoccursatthepointwhereMohr’s

circleintersectsthefailureenvelopewithslope(μ).

SaltwateriseitherdisposedintothesedimentaryupperArbuckleGrouporinthebase-

mentrock.Lowporosityandpermeabilityofthebasementrockactsasabarriertothemi-

grationofinjectedwaterbothlaterallyandvertically.NotethattheArbucklesedimentary

unitisunder-pressured.Lowpermeabilityofthebasementmatrix(10-15-10-18m2)re-

quiresfaultswithhighpermeability(10-12m2)tocreatehighpermeabilitypathwaysfor

increaseinporepressure.

Increaseintheporepressureinthebasementrockawayfromthewellboreisduetopore

pressurediffusion(P.TalwaniandAcreeS,1984):ծ p/ծ t=D*Δ2p,whereDishydraulicdiffusivity.Permeabilityisdirectlyproportionaltodiffusivity.Thisexplainsthetimelag

betweenearthquakeandwaterinjection(~8-10yrs.)andalsohypocentrallocationof

earthquakeatlargedistance(Horizontally~10km)anddepth(vertically~3.5-5km)from

theinjectionwell.

Figure.7.4:Probabilitydensityfunctionofthea)Dipofthefaultb)faultrakec)faultorientation(DaroldandHolland,2015)

73

7.3PorePressureModeling

Thissectiondescribestheporepressuremodelingworkattemptedinthisstudytoassess

changesinporepressurelaterallyandverticallyinthereservoirasafunctionofwaterin-

jectionrateanddurationofinjection.Forthissectionoftheflowsimulationmodeling,we

havenotaccountedforlocalstresschanges.Theunderlyingmotivationforthispartofthe

studywastoinvestigatetheroleofreservoirpropertiessuchaspermeability,faulttrans-

missibility,injectionrateanddurationofinjectiontoquantifytheimpactonporepres-

sures.Anincreaseof0.01to0.1MPaofstressissufficienttotriggerearthquakeswhen

faultsarenearfailureconditionorwhereearth’scrustiscriticallystressed.(R.A.Harris,et

al,1995,Keranenetal,2015).

7.3.1ModelGridSpecification

Thefollowingdataprovideanoverviewofthemodelgridemployedtounderstandpore

pressurevariationsinresponsetofluidinjectionintheOklahomaCityField.Becausewe

donothaveaccesstoageologicmodel,thestudyisrestrictedtothebestpossiblerepresen-

tationofthegeologyofthefield.ThemodelisshowninFigure7.5.

1. TotalstudyArea:35*35km(AreaofOklahomaCity)2. Depth=2kmto8km(Keranenetal,2015)3. Totalnumberofgridcellinx,y,zdirection=(i,j,k):(175,175,25)4. Oil-WaterContact(OWC)at2000mbelowthesurface.Waterisinjectedinthesalt-

wateraquifer.Thereisnooilinthemodel.

5. Positionofwellongrid:(X,Y)=(90,100).Thiswouldrepresentawelllocatedinthecenterofthestudyarea.

6. Numberofparallelfaultsused:4.Distancefromthewells:a. Fault1:11.6kmfromthewell;b. Fault2:5kmfromthewell;c. Fault3:1.6kmfromthewell;d. Fault4:13kmfromthewell:e.

7.3.2SimulationCaseStudies

Themodeldescribedinaprevioussectionisrunfortwodifferentvaluesofthefaulttrans-

missibilitymultiplier.Theseare0.5and1.Thesaltwaterinjectionratesarechosentobe

18,000,30,000,54,000and75,000sm3/month.Thedurationofwaterinjectionis10years.

Theresultingchangesinthestressondifferentfaults(inMPa)withdifferentinjectionrates

isshowninFigure7.6asafunctionoftimeforafaulttransmissibilityof1.

Withthemodelruntimeof10years,anexcessporepressureofupto0.018MPadevelops

onthenearestfault.Asnotedearlier,thismaybesufficienttotriggerseismicityforcriti-

callystressedfaults.Figures7.7to7.9documentporepressurevariationsinaverticalslice

ofthesubsurface.Theporepressureundercertaininjectionratescanexceedthecriterion

forfailureofcriticallystressedfaults.Withafaulttransmissibilitymultiplierof0.5,

changesintheporepressurearesimilartothecasesstudiedaboveanddonotshowappre-

ciabledifferences.

74

7.4.CoupledFlowandGeomechanicsSimulation

Inthissection,wedescribeacoupledflowandgeomechanicalsimulationtoinvestigate

changesinstresswithincreasesinvolumesofwaterinjected.Fromtheporepressure

modelingresultsshowninaprevioussection,athigherinjectionrates,theincreaseinthe

porepressureexceedthethresholdvaluetotriggerslippage.Becauseouranalysisisre-

strictedtotheOklahomaCityField,thestressconditionandfaultstrikeissimilartothose

showninFigure7.3.Themodelingisrestrictedto75000sm3/dandtheobjectiveistoes-

timatethetimetoslippageforapre-existingfault.Becauseoffriction,aspecificvalueof

shearstressmustbepresentinarockbeforefrictionalslidingisinitiatedonpre-existing

fractures.FailurecriterionforfrictionalslidingissimilartotheMohr-Coloumbfailurecri-

teriaandplotsasaasastraightlineontheMohr’sdiagramasseeninFigure7.11.This

empiricalrelationshipisdescribedbyByerlee’slaw(BenandStephan,2004).Cohesionis

zeroforpreexistingfaultedrock.

TheplasticmodelformationpropertieswerederivedfromGereandTimoshenko(1997).

FortheArbucklelimestone,theseare:

1. Elasticmoduli:0.005E+6MPa2. Poisson’sRatio:0.273. Cohesion:0.001.Thevalueistakentobesmallforpre-existingfaults.

Forthebasement(graniticrock),theseare:

1. Elasticmoduli:0.01E+6MPa2. Poisson’sRatio:0.233. Cohesion:0.001.4. Initialstressvaluesaregivenatthetopofthereservoiri.e.6,561.68ftbelowsurface

aregivenasinTable7.2.

Theverticallithostratigraphicstressgradient=1psi/ft(ZobackandZoback,2003).The

horizontalstressesareobtainedfromZobackandZoback(2003).Therelativemagnitude

oftheprincipalstresses,Scanberelatedtothefaultingstylecurrentlyintheregion.Be-

causeOklahomapredominantlyhasstrikeslipfaults,wehavemodeledstrikeslipfaultsin

thebasementwithnofaultsintheArbuckle.Therelationshipbetweentheprincipal

stressesisgivenby:

1. Arbuckle,normalfaulting:Svertical>Shorizontal,max>Shorizontal,min2. Basement,strike-slipfault:Shorizontal,max>Svertical>Shorizontal,min

Table7.2:Valuesspecifiedforthehorizontalmaximumandminimumstressesaswellasthecorrespondinggradients.

Shorizontal,max Shorizontal,min Svertical

Stressatthetopof

thereservoir,psi

5500 4280 6562

Stressgradient,psi/ft -1.5 -0.618 -1.0

75

(a)

(b)

Fig.7.5:a)Schematicdiagramofthereservoirboundaryshowingbasementfaultimpressiononthetopofthereservoir(Arbuckle)b)SegmentationFaultintheBasementandwellpositionwithmaximumwelldepthintheupperArbuckleFormation.Becausewehavenotconsideredtheeffectofstressinthisstudy,faultisnotinaccordancewiththestress(optimumstressdirectionshouldbeatspecificangletothefaultasdescribedinalatersection).

Arbuckle

Basement

76

Fault4(13kmfromthewell) Fault3(1.6kmfromthewell)Fault1(11.6kmfromthewell) Fault2(5kmfromthewell)

Figure.7.6:Changesinporepressureonfaultsatvaryingdistancefromtheinjectionwell.Thresholdtotriggerearthquakesisintherangeof0.01-0.1MPa.Differencesinchangeinporepressurewiththefaultspositionisrelativelylow.Withincreasesininjectionrate,excesspressuredevelopedonthefaultsdependsondistancetotheinjectionwell.

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0 500 1000 1500 2000 2500 3000 3500 4000

chnageinpressure(M

Pa)

Changeinporepressurewithtime.

2337days

Days

Figure7.7.Thefigureshowsthechangesinporepressureafter10yearsofwaterinjectionattherateof18000sm3/month.Thefigureisaverticalsectionofthereservoirperpendiculartothefaultsandpassingthroughwell.Increaseofporepressureisabout~0.003MPaintheentirereservoir.Nearthewellbore,themaximumincreaseobservedis~0.009Mpa.

76

Fault4(13kmfromthewell) Fault3(1.6kmfromthewell)Fault1(11.6kmfromthewell) Fault2(5kmfromthewell)

Figure.7.6:Changesinporepressureonfaultsatvaryingdistancefromtheinjectionwell.Thresholdtotriggerearthquakesisintherangeof0.01-0.1MPa.Differencesinchangeinporepressurewiththefaultspositionisrelativelylow.Withincreasesininjectionrate,excesspressuredevelopedonthefaultsdependsondistancetotheinjectionwell.

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0 500 1000 1500 2000 2500 3000 3500 4000

chnageinpressure(M

Pa)

Changeinporepressurewithtime.

2337days

Days

Figure7.7.Thefigureshowsthechangesinporepressureafter10yearsofwaterinjectionattherateof18000sm3/month.Thefigureisaverticalsectionofthereservoirperpendiculartothefaultsandpassingthroughwell.Increaseofporepressureisabout~0.003MPaintheentirereservoir.Nearthewellbore,themaximumincreaseobservedis~0.009Mpa.

77

Figure7.8.Thefigureshowsthechangesinporepressureafter10yearsofwaterinjectionattherateof30,000sm3/month.Thefigureisaverticalsectionofthereservoirperpendiculartothefaultsandpassingthroughwell.Increaseofporepressureisabout~0.004MPaintheentirereservoir.Nearthewellbore,themaximumincreaseobservedis~0.014Mpa.

Basement

Well

Basement

Figure7.9.Thefigureshowsthechangesinporepressureafter10yearsofwaterinjectionattherateof54000sm3/month.Thefigureisaverticalsectionofthereservoirperpendiculartothefaultsandpassingthroughwell.Increaseofporepressureisabout~0.01MPaintheentirereservoir.Nearthewellbore,themaximumincreaseobservedis~0.018Mpa.

BasementBasement

78

FortheArbuckle(Normalfaultingzone),minimumhorizontalstressisbasedaccordingto

Shorizontal,min=0.67*Svertical,givingavalueof4,280psiforShorizontal,min(TownendandZoback,

2000).Thedifferencebetweenthemaximumstressandminimumhorizontalstressmagni-

tudeislow.Therefore,withalackofpublishedvaluesforthemaximumhorizontalstress,

weassumeavalueof5000psiforShorizontal,min.Themagnitudeofthestressgradientisob-

tainedfromWalshandZoback(2015).Withthisstressgradient,thestressregimechanges

fromnormalfaultingintheArbuckletostrikeslipfaultinginthebasement.

Thestressgradientforthehorizontalmaximumstressinthebasementisobtainedfrom

TownendandZoback(2000).Additionally,thestressmagnitudeoftheearth’scrustis

specifiedtobecriticallystressed.Therelationshipbetweenmaximumstressandminimum

stressduringfaultingisgivenbyJaegerandCook(1971)asσ3/σ1=((µ2+1)1/2+µ)2,where,

µ=coefficientoffriction=0.6inthemodel.

7.4.1.One-wayFlow-GeomechanicalCouplingModelDescription

Themodelisdescribedona96*96*15Cartesiangridwithatotalareaof14.5km*14.5km.

ThedepthoftheArbucklegroupwithathicknessof750misbetween2.0kmand5.74km.

Thegranitebasementisspecifiedtobe3000mthick.Theoptimalpre-existingfaultdirec-

tionisspecifiedtobe105degreesto120degreesfromDaroldandHolland(2015).The

optimalfaultdirectionrepresentsfaultsmorelikelytobeassociatedwithanearthquakein

thecontemporarystressfield.ThemaximumhorizontalstressorientationisN85°E.The

faultstartfromthebaseoftheArbuckleandextendsthroughoutthebasementgraniteand

isspecifiedtobe500mfromtheinjectionwell.Waterinjectionrateisspecifiedtobe3000

STB/day.Thewatersaturationwithinthesaltwateraquiferisassumedtobe100%.

Figure7.10.Thefigureshowsthechangesinporepressureafter10yearsofwaterinjectionattherateof75000sm3/month.Thefigureisaverticalsectionofthereservoirperpendiculartothefaultsandpassingthroughwell.Increaseofporepressureisabout~0.016MPaintheentirereservoir.Thisfallsinthethresholdrangeforfaultfailure.Nearthewellbore,themaximumincreaseobservedis~0.023Mpa.

79

AmodeldiagramisshowninFigure7.12.

7.4.2.SimulationResults

Thesimulationresultsindicatethatamaximumchangeinthepressureofcloseto12psiais

observedatadepthof5.4kmfromthesurfaceadjacenttothefaultthatis500mawayfrom

theinjectionwell.

7.5.References

1. Walsh,F.R.,andZoback,M.D.(2015)Oklahoma’srecentearthquakesandsaltwaterdisposal.Sci.Adv.2015;1:e1500195,18June2015

2. DaroldA.P.,Holland,A.,Morris,J.K.,andGibson,A.,R.(2015),OklahomaEarthquakeSummaryReport2014,Okla.Geol.Surv.Open-FileReport,OF1-2015.

Figure7.11.Graphofshearstressandnormalstressvaluesattheinitiationofslidingonpreexistingfracturesinavarietyofrocktypes.Thebest-fitlinedefinesByerlee’slaw(BenandStephan,2004).Fromabovewecanseethatshearstressrequiresforthefaultslippageislessthanthefaultfailureofintactrock(Mohr-Coulombfailureenvelope).

Cohesion

forintactrock

80

Figure7.12.Schematicdiagramofthereservoirboundary,BasementFaultimpressiononthetopofthereservoirinthefigureontop.ThefigurebelowshowsarepresentativemodeloftheAr-buckleformationwithassociatedbasementlayersandthefaultinbasementinblueandinitialstressdirection(Redarrowshowingmaximumhorizontalstresscondition)(Distanceinft).

81

Figure7.13:Alinearincreasesinpressureisobservedinalllayersofthemodelasafunctionoftimeandin10yearsofwaterinjection,a12psiincreaseinpressureisobserved.

Figure7.14.Changeinmaximumstressontheleftandtheminimumstressontherightasafunctionoftime.Thereisanegligiblechangeinthemagnitudeofthemaximumstress.However,theminimumstressisdecreasedbyabout2psi.

82

Figure7.15.Effective-stressstateatadepthof4600mwithafaultzone40mfromtheinjectionwellwithpermeabilityof250mD.Thecoefficientoffrictionistakenas0.6.Cohesionistakenaszeroforthepreexistingfault(Townend,J.,andZoback,M.D.(2000)).FC=FrictionCoefficient.

8. DaroldA.P.,Holland,A.,ChenC.,A.Youngblood(2014),PreliminaryAnalysisofSeismicityNearEagleton1-29,Cartercounty,July2014,Okla.Geol.Surv.Open-File

Report,OF2-2014.

9. JeremyBoak,(2016),OklahomaEarthquakesandInjectionofProducedWater,OGSSurvey,2016.

10. RichardD.Fritz,PatrickMedlock,MichaelJ.Kuykendall,andJ.L.Wilson(2013),Geol-ogyoftheArbuckleGroupintheMidcontinent:SequenceStratigraphy,ReservoirDe-

velopment,andthePotentialforHydrocarbonExploration,AAPGAnnualConvention

andExhibition,2013.

11. WilliamEHam,RegionalGeologyoftheArbuckleMountains,Oklahoma,TheGeologi-calsocietyofAmerica,1973

12. Morgan,BC,andMurrayKE(2015)CharacterizingSmall-ScalePermeabilityoftheAr-buckleGroup,Oklahoma.OklahomaGeologicalSurveyOpen-FileReport(OF2-2015).

Norman,OK.12pages.

13. Murray,K.E.(2015)ClassIISaltwaterDisposalfor2009-2014attheAnnual-,State-,andCounty-ScalesbyGeologicZonesofCompletion,Oklahoma.OklahomaGeological

SurveyOpenFileReport(OF5-2015)

14. DaroldA.P,A.A.Holland(2015),PreliminaryOklahomaOptimalFaultOrientations,OGSopenreport,OF1-2015

Effectivenormalstress(MPa)

Shearstress(M

Pa)

Cohesion=0,preexistingfault

83

15. MarkDZoback,andMaryLZoback(2002),StressintheEarthLithosphere,Encyclopediaofscienceandtechnology,3rdedition,volume16,2002

16. Townend,J.,andZoback,M.D.(2000)Howfaultingkeepsthecruststrong,Geology28,399-400

17. RichardC.AltandMarkD.Zoback(2015),ADetailedOklahomaStressMapforIn-ducedSeismicityMitigation.AAPGConventionandExhibition,2015.

18. TalwaniP.andAcreeSteve(1984),PorePressureDiffusionandtheMechanismofReservoir-InducedSeismicity.PAGEOPH,Vol.122.

19. WilliamL.Ellsworth(2013),Injection-InducedEarthquakes,Science341,201320. RuthA.Harris,RobertW.SimpsonandPaulA.Reasenberg(1995).InfluenceofStatic

StressChangesonEarthquakeLocationsinSouthernCalifornia.Nature.Vol375.

21. MurrayKE(2015)ClassIISaltwaterDisposalfor2009–2014attheAnnual-,State-,andCounty-ScalesbyGeologicZonesofCompletion,Oklahoma.OklahomaGeological

SurveyOpen-FileReport(OF5-2015).Norman,OK.pp.18.

22. RallWalshandMarkZoback,(2015)ProbabilisticGeomechanicalAssessmentofPotentiallyActiveFaultsinNorthCentralOklahoma.

23. JaegerJ.C.andCook,N.G.W.,(1971)FundamentalsofRockmechanics.24. JamesM.Gere,StephenP.Timoshenko,(1997),MechanicsofMaterial.25. Keranen,K.Metal.(2014).SharpincreaseincentralOklahomaseismicitysince2008

inducedbymassivewastewaterinjection.Science:448-451.

84

DescriptionofRPSEAProjectTask11–IntegratedRockMechanicsStudies

Availablerockproperties,in-situstressestimates,observedseismicdata,andnaturalfrac-turedistributions,shallbeusedtocomputetheporepressureandthestressconditions

neededtobringtherockmassintocriticalstate.

Availableseismicdataandknowledgeofthetectonicframeworkoftheregionshallbeused

toestimatethein-situstresses,anddeterminediscontinuityorientationsandtheirme-chanicalproperties.Resultsfromanalysisofseismicwaveformsshallprovidethedistribu-

tionandorientationsofshearandpossibletensileevents,thefractureorientationsob-

tainedfromeventclusters,andestimatesoftheamountofslipfromwaveformanalysis.

Thenanalysisofhowthereservoirrockshouldfailinresponsetoinjectionshallbedone.A

3Dconceptualmodeloftheresponseofthereservoirtothestimulationsshallbeused.

A3Dmodelthatconsidersporepressureandstresseffectsshallbeusedtomodelmorede-

tailsofthemicroseismicevents.Thespatio-temporalpressuredistributionswithinthe

modelshallbeobtainedontheirregularlyspacednodesofthegridandcriticalityorrock

failurecriterion(triggeringcriterion)shallbedefinedthroughthereservoir.Oncethe

criticalityconditionissatisfied,asyntheticcloudofseismiceventscanbecreatedbycom-

paringitwiththethresholdvalueforeachcellintherockandateachtimestep.Themodel

parametersshallbeadjustedbymodifyingdiffusivity,stress,andcriticallyparametersto

matchthecharacteristicsoftheobservedmicroseismicity.

Thereportappendedbelowsummarizesintegratedrockmechanicalstudies,supportedbytheRPSEAProject.

5. IntegratedRockMechanicsStudiesAhmadGhassemiMewbourneCollegeofPetroleumandGeologicalEngineering,SarkeysEnergyCenter100EastBoydSt.,Norman,Oklahoma73019-0628

EarthquakesinthecontinentalinterioroftheUnitedStateshavehistoricallybeenrare,but

startingin2009therewasasignificantincreaseinthenumberoffeltevents.Aprominent

examplearethefourearthquakeswithmagnitudesof4.0orgreater,includingoneM5.7

earthquake,nearPrague,OklahomainNovember2011.Theseearthquakesledtowide-

spreadconcernaboutpotentialdamagefrominducedseismicity.

TheearthquakesoccurredclosetoClassIIUndergroundInjectionControlwellsforsaltwa-

terdisposal(SWD)fromoilandgasoperations.Theinjectedwaterincreasesporepres-

surewithinthetargetlayerandcanpressurizedeepercrystallinebasementrocksvianatu-

ralfracturesystemsandfaults.Ithasbeensuggestedthatthishasledtopressurization

andstressredistributionwithinthebasement,causingfaultreactivationandincreased

seismicity.

AlmostallstudiesontheincreasedseismicityincentralOklahomahavefocusedonpore

pressureeffectswithoutexplicitconsiderationoflarge-scalerockmassdeformation.In

thisstudy,wedevelopalarge-scalegeomechanicalconceptualmodelforthefaultssystem

andassessitsresponsetosaltwaterinjection.ThisportionoftheRPSEAProjectaimsto

85

understandtheeffectofwaterinjectiononporepressureincreaseanditsconsequences

withintheWilzettafaultzonenearPrague,Oklahoma,UnitedStates.Wesimulatethehy-

draulicoverpressuresandpotentialforinducedseismicityduringhydraulicinjection.

Thestudyareaselectedformodelingsaltwaterinjection,encompassingapproximately

460squarekilometers(approximately22×23km)isshownbythebluerectanglein

Figure8.1aandb(FaultdatabasefromOGS,

http://www.ou.edu/content/ogs/data/fault.html).Selectionofthissitewasbasedonthe

increasednumberofearthquakeeventsinthisarea.Thelocationofinjectionwells(shown

inFigure8.1c)andrelatedinformationsuchasrate,volume,anddurationofinjectionare

extractedfromreporteddatabyOGSandtheOklahomaCorporationCommission

(http://www.occeweb.com/og/ogdatafiles2.htm).Locationsandmagnitudesof

earthquakes(showninFigure8.1d)werefoundinasimilarfashion.Figure8.2shows

differentsubsurfacegeologicunitsrelevanttothiswork.

(a) (b)

(c) (d)

Figure8.1:(a)and(b)Generalstudyarea.Focusareaextentsinblue.Tracesofsignificantfaultsshownasredlines.(c)Locationofinjectionwellsintheareaofinterest.(d)Seismiceventsbetween2009and2011.

86

2 Figure8.2:Stratigraphicorrelationchartofgroups,sub-groupsorformationscomprisinginjectionzones(MurrayandHolland,2014).

87

Ourmodelincludestwomajorfaults;theWilzettafault(WFZ)andtheMeeker-Praguefault

(MPF),showninFigure8.1cand8.1d.TappandDycus(2013)showthatthe~N25-30E

trendingWFZisarelativelylong,narrowzoneofhigh-anglenormal,strike-slip,andre-

versefaults.TheMeeker-Praguefaultstrikes~N55EandobliquelyintersectstheWilzetta

fault.Weusedtheubiquitous-jointmodeltomodelthefaults.

AninventoryoffluidinjectionvolumesbyMurrayandHolland(2014)indicates4,124ac-

tiveSWDwellsinOklahomain2011.Figure8.3showsthevolumeoffluidsthatwerein-

jectedintodifferentzonesusingClassIIUICwellsduring2011.FLAC3D(acoupledflow

geomechanicalcode)isusedinthispartoftheworktosimulatepressurebuildupandfluid

migration,stressanalysis,andfaultmotion.Thesimulationdomainanditsdimensionsare

showninFigure8.4.Thesimulationdomainisa50km×50kmarea,andconsistsofthree

layers;theSimpsongroup,theArbucklegroup,andthebasement,withaveragethickness

of180m,650m,and850m,respectively.Theselayersaretheonesthathavebeensub-

jectedtosignificantinjection(Figure8.3).

Thepresenceofotherlayersisconsideredthroughtheircontributionstothevertical

stress.AccordingtodatacompilationbyCrain(2015,unpublisheddata),thedeepest

earthquakehasoccurredatadepthof12km,butfornowourmodelincludesthebasement

toadepthof3kmtoreducethecomputationtime.

Theimportantinputparameterofin-situstressisnotwellknowninthestudyarea.To

generateareasonablestressstateinthesimulationdomain,weintroducegravityloading

(thedensityis2305kg/m3)forthelithostaticstress,andsettheSH,maxandSh,mintoas27.1

MPaand15.3MParespectively(Hair,2012).SH,maxorientationisassumedtobeinthe

east-westdirectionandSh,minisperpendiculartoit.Weassumethatthelateralboundaries

Figure8.3:FluidinjectionvolumesinjectedintostratigraphiczonesinOklahoma,2011(MurrayandHolland,2014).

88

arefixedinthehorizontaldirections(xandy-direction).Rollersareusedatthebasesothattheverticaldisplacementisfixedinthez-direction.Theuppersurfaceofthesimula-tiondomain,whichistheboundarywiththeViolalayerisfreetomovevertically.Fig.8.4

showstheinitialconditionofstressbeforeinjection.Theinitialporepressureofthemodel

isconsideredtobe5MPa;thisvaluecanbeadjustedforgreateraccuracyinthefuture.

TheMohr-Coulombmodelisusedfortherocks,andtheelasticpropertiesareasfollows:

bulkmodulus(K)is13.2GPa,shearmodulus(G)is11.6GPa,frictionangle(φ)is46.2°and

cohesionis17.6MPa.Currently,allthreelayersareassumedtohavethesamemechanical

properties(whichisobviouslyanincorrectassumption).Infuturesimulationseachlayer

willbegivenitsownsetofpropertiesbasedonlabmeasurements.

Figure4:Domainanddimensionsofthemodel.

Table8.1showssubsurfacelayersandtheircorrespondinghydraulicproperties.Thefluid

isconsideredanincompressiblebrineandhasadensityandbulkmodulusofabout1110

kg/m3and2.15GPa,respectively(PotterandBrown(1977).

Thissimulationdomainisdividedinto876,932gridpointsand729,668elements.The

faultzonesaremeshedbyrefiningthezonesalongthefaultsandassigningtheubiquitous

89

modeltothezoneswhichcrossthefaults.Sotheubiquitousjointdirectionsareparallelto

thefaultdirectiontosimulatethefaulteffect.

Thediffusivitycoefficient,definedasthemobilitycoefficient,k,dividedbystorativity,S,fortheArbucklelayercanbeobtainedbythefollowingequation:

34

1 2

GKM

kSkc

++

==a

(1)

whereMistheBiotmodulus,αistheBioteffectivestresscoefficient(M=Kf/nandα=1forincompressiblegrains),Kisthedrainedbulkmodulus,Gistheshearmodulus(Cheng,2014).

Fromthisequation,thediffusivitycoefficientfortheArbucklelayeris1.6m2/s.

ThefirststepofthemodelingworkinthisstudywasconductedwiththeFLAC3Dcode,

consideringtopography,andspatialgeometryoffaultsanddifferentformations.The

domainismorethan22kmintheeast-westandnorth-southdirection,andvariesindepth

toabout3000m(Figure8.2).Themodelconsistsofsevenlayers;threeofthemarethe

targetoftheinjection(theHuntongroup,theSimpsongroup,theArbucklegroup)andthe

bottomlayer(thebasement)isthelocationofmostearthquakes.Zonessurroundingthe

faultsarerefinedtomoreaccuratelyreflectthefaultzone.Asmallersubdomainhasbeen

simulatedbyexcludingthelayerswhichhaveaminorvolumeofinjectionandreducingthe

domainsizetoapproximately5×6km.Inthisway,wecanassessresponseofthesystem

faster,andifneededmodifythemodel.Therocklayersareassignedthebuilt-inMohr-

Coulombplasticityconstitutivemodel.Thepresenceofnaturalfracturesintherockmass

isalsoconsidered.

Afterapplyinginitialandboundaryconditionsofthemodel,andlettingthesystemreach

theequilibrium,injectionwascommencedandcontinuedfor19years(1993to2011)us-

ingreporteddata(injectionrateandwellpressure).Wemonitorchangeofstresscondi-

tion,redistributionoftheporepressureinthedomain,anddisplacementalongthefaultsto

evaluatethepossibilityofinducedseismicity.

Figure8.5showstheporepressuredistributionbeforeinjectionandafter14yearsofinjec-

tion.Itsuggeststhatinjectioncanchangetheinitialporepressurebyasignificantamount

(6MPa)alongthefault(fortheassumedboundaryconditions),whichreducestheeffective

stress.Figure8.6showstheinduceddisplacementintheXandYdirectionsafter14years

Table8.1:Subsurfacelayersandtheircorrespondinghydraulicproperties

Rockstratigraphic

unit

Topoftheunitelevation

(metersbelowsealevel)

Permeability(

md)

Porosity

(%)

SimpsonGroup 1100-1350 80 20

ArbuckleGroup 1250-1550 400 25

Basement 1800-2200 70 20

90

(a) (b)

Figure8.5:Porepressuredistributionforimpermeableboundarya)beforeinjectionb)after14

yearsofinjection.

(a) (b)

Figure8.6:a)x-displacementandb)y-displacementofthemodelafter14yearsofinjection.

ofinjection,whichgivesanindicationofthepotentialforearthquakes.Intheabsenceof

sufficientdataforhydraulicandmechanicalpropertiesofsomelayersanduncertain

boundaryconditions,thecurrentresultsshouldbeusedinaqualitativemannertounder-

standthetrend.

91

Ontheexperimentalside,multi-stagetestshavebeencarriedonone-inch-diameterFort

SillLimestoneplugsandTroyGraniteplugs.Allthesamplesaredriedandunderun-

drainedtestcondition.Thedatawereusedtoconstructfailureenvelopesfortheserocks.

TheresultsareshowninFigures8.7and8.8below.Otherimportanttestwerenotcarried

outduetobudgetconstraints.

References

Cheng,A.H.D.(2014).Fundamentalsofporoelasticity.AnalysisandDesignMethods:Com-

prehensiveRockEngineering:Principles,PracticeandProjects,113.

Tapp,B.,&Dycus,M.(2013).StructuralCharacterizationoftheWilzettaFaultZone;Lin-

coln,Pottawatomie,andCreekCounties,Oklahoma.InMid-ContinentSection.

Hair,T.J.(2012).ConstructingageomechanicalmodeloftheWoodfordShale,Cherokee

Platform,Oklahoma,USAeffectsofconfiningstressandrockstrengthonfluidflow.

Murray,K.E.,&Holland,A.A.(2014).InventoryofclassIIundergroundinjectioncontrol

volumesinthemidcontinent.

Hubbert,M.K.,andW.W.Rubey(1959),Roleoffluidpressureinmechanicsofoverthrust

faulting:1.Mechanicsoffluid-filledporoussolidsanditsapplicationtooverthrustfaulting,

Geol.Soc.Am.Bull.

ItascaConsultingGroup(2012):FastLagrangianAnalysisofContinuain3Dimensions

(FLAC3D),Minneapolis,MN,USA.

Keranen,K.M.,H.M.Savage,G.A.Abers,andE.S.Cochran(2013),Potentiallyinduced

earthquakesinOklahoma,USA:Linksbetween5.7earthquakesequence,Geology.

Keranen,K.M.,M.Weingarten,G.A.Abers,B.A.Bekins,S.Ge(2014),Sharpincreaseincen-

tralOklahomaseismicitysince2008inducedbymassivewastewaterinjection,Sience.

92

Figure8.7.MohrCirclesandMohr-CoulombEnvelopeofArbuckleSampleAr-4.

Figure8.8.MohrCirclesandMohr-CoulombEnvelopeofbasementGraniteSampleTr-4.

y = 1.0475x + 6895.7

0

10000

20000

30000

0 10000 20000 30000 40000 50000 60000

Shea

r St

ress

, psi

Normal Stress, psi

Mohr-Coulomb Envelope

y=1.2934x+9576

0

20000

40000

60000

0 20000 40000 60000 80000 100000

ShearStress,psi

NormalStress,psi

Mohr-CoulombEnvelope

93

DescriptionofRPSEAProjectTask3.0-TechnologyTransfer:SUBCONTRACTORshallworkwithRPSEAthroughouttheprojecttodevelopandimplementaneffectiveoverallTechnol-ogyTransferprogram.TheSUBCONTRACTORshallparticipateinallappropriateRPSEAworkshopsandshallregularlypresentresearchresultsatprofessionalmeetingssuchastheannualmeetingsoftheSocietyofExplorationGeophysicistsandAmericanAssociationofPetroleumGeologists.TheSUBCONTRACTORhasalonghistoryofhostingregionalworkshopsandshallannuallyhostworkshopsontopicssuchasitsrecentoneonFluidInjectionInducedSeismicity.Technologytransferactivitiesshallalsobedetailedinthe

ProjectManagementPlan.SUBCONTRACTORshallreportthecostassociatedwithprojectleveltechnologytransferactivitiesoneachmonthlyreportandinvoice.

ThereportappendedbelowsummarizestechnologytransferactivitiessupportedbytheRPSEAProject.

10. TechnologyTransferActivitiesPublications

ChenC.,andA.A.Holland(2016)PhasePApy:ARobustPurePythonPackageforAutomatic

IdentificationofSeismicPhases,SeismologicalResearchLetter.

Theauthorsprovidedtheprogrampackageofversion1.1tothepublicthroughGitHub

https://github.com/austinholland/PhasePApy.Version1.0hasbeenusedbyOklahoma

GeologicalSurvey(OGS)fornearrealtimeearthquakemonitoringsince2014.

Darold,A.P.,andA.A.Holland(2015)PreliminaryOklahomaOptimalFaultOrientations

OklahomaGeologicalSurveyOpen-FileReport,OF4-2015.

http://wichita.ogs.ou.edu/documents/OF4-2015/.

Darold,A.,A.A.Holland,C.Chen,andA.Youngblood(2014),PreliminaryAnalysisofSeis-

micityNearEagleton1-29,CarterCounty,July2014,Okla.Geol.Surv.Open-FileReport,OF2-2014,17.

Holland,A.A.(2014),ImagingtimedependentcrustaldeformationusingGPSgeodesyand

inducedseismicity,stressandoptimalfaultorientationsintheNorthAmericanmid-conti-

nent,UniversityofArizona,Tucson,Arizona,USA.

Holland,A.A.(2015),PreliminaryFaultMapofOklahoma,OklahomaGeologicalSurvey

OpenFileReport,OF3-2015..OF3-2015|Shape-file(GIS)|Supplemental

McNamara,D.E.,H.M.Benz,R.B.Herrmann,E.A.Bergman,P.Earle,A.Holland,R.Baldwin,

andA.Gassner(2015),EarthquakehypocentersandfocalmechanismsincentralOklahoma

revealacomplexsystemofreactivatedsubsurfacestrike-slipfaulting,GeophysicalResearchLetters,.

Murray,K.E.(2014),ClassIIUndergroundInjectionControlWellDatafor2010-2013by

GeologicZonesofCompletion,Oklahoma,Okla.Geol.Surv.Open-FileReport,OF1-2014,32.

Murray,K.E.,andA.A.Holland(2014),InventoryofClassIIUndergroundInjectionControl

VolumesintheMidcontinent,ShaleShaker,65(2),98-106.

OklahomaGeologicalSurvey,April21,2015OGSStatementonOklahomaEarthquakes

94

Toth,C.R.(2014),SeparationoftheEarthquakeTomographyInverseProblemtoRefine

HypocenterLocationsandTomographicModels:ACaseStudyfromCentralOklahoma,59

pp,UniversityofOklahoma,Norman,OK,USA.

U.S.GeologicalSurveyandOklahomaGeologicalSurvey,2014,USGSOGSJointPressRe-

leaseMay5,2014(PDF)

Workshops

InNovember2014,TheOGSco-hostedaworkshopwiththeUSGS.ThetitlewasWorkshop

onHazardfromInducedSeismicitywithabout140peopleinattendanceandanother42

participatedviaawebinar.Themeetingwastwodayslongwithonedayforthebroadsci-

entificcommunityandthepublic.Theseconddaywasamoretargetedmeetingwiththe

USGS,additionalresearchers,andthesteeringcommitteefortheNationalSeismicHazard

Maps.Moreinformationontheworkshopisavailableat

https://sslearthquake.usgs.gov/regional/ceus/workshop/.Theagendaforthismeetingis

providedonthefollowingpage.

TheUSGSisresponsibleforregularlyupdatingseismichazardmapsthatinformregulatory

bodiesandimpactupdatesofbuildingcodes.Themostrecentversionofthemapdidnot

includeseismiceventsthatwereinterpretedasbeinginduced.Asaresultofthiswork-

shop,thisstanceisbeenreversedandallseismicitywillbeconsideredinthenewmap.The

firstversionofthatmapwasissuedbytheUSGSinMarch2016,andshowstheoneyear

likelihoodofadamagingearthquakeintheUnitedStates.EarthquakeprobabilitiesforOk-

lahomaarederivedfromthecatalogofearthquakesinterpretedtobemainlyinduced.

Anotheroutcomeofthismeetingwastechnologytransfertoregulatorybodiesandduring

thismeetingtheOklahomaandKansasCorporationCommissionshadaveryproductive

discussionwithourresearchteam.Inabroadercontext,weareregularlyexchangingin-

formationbetweenourresearchgroup,regulatoryagencies,andindustry.

TheTechnologyTransferWorkshop:SeismicityinOklahomawasheldSeptember7-8,

2016attheMoore-NormanTechnologyCenterinNormanOKtogatherresearcherswork-

ingonvariousaspectsofseismicityinOklahoma,emphasizingthoseresearchersbasedin

Oklahoma(butincludingotherswithsignificantresearchprogramsinOklahomaandad-

joiningstates(Texas,Arkansas,andKansas).Theworkshopwasattendedbyabout140re-

searchersfromOklahomaandelsewhere,inGovernment(USGS,OGS,OklahomaCorpora-

tionCommission,KansasandArkansasGeologicalSurveys,TexasBureauofEconomicGe-

ology,DOE,NETL,EPA)Universities(UniversityofOklahoma,OklahomaStateUniversity,

UniversityofTexas,UniversityofColorado,StanfordUniversity,etc.)andindustry(Devon,

Chesapeake,ExxonMobil,Pioneer,WhiteStarPetroleum,Newfield,Cimarex,SandRidge,

XTO,Marathon,OklahomaOilandGasAssociation,OklahomaIndependentPetroleumAs-

sociation,GEGlobalResearch,CH2M).TheWorkshopAgendaisprovidedfollowingthe

previousworkshopagenda.

95

Welcome and Background· Welcome -- Oklahoma Geological Survey – Keller, Holland (15 min)

· Welcome USGS – Rubinstein and Petersen (20 min)

· Overview of Induced seismicity – Ellsworth (20 min)

· A Case Study Of Seismicity In Azle, Texas – DeShon (20 min)

15 min Break

Part 1: The National Seismic Hazard Model and Potentially Induced Seismicity · How Is The NSHM Put Together? What Are The Key Factors That Influence Hazard? –Mueller (30 min)

· Is Mmax Different For Induced Seismicity? (15 min)

· Ground Motions And Source Properties Of Natural Vs Induced Earthquakes (15 min)

· How Does Varying Smoothing Affect Hazard? Moschetti (15 min)

· Discussion (15min) 15 min break

Part 2: The Logic Tree · Overview Of The Logic Tree To Assess Hazard From Varying Earthquake Rates –Rubinstein (20 min)

· The Potentially Induced Seismicity Model: Sensitivity To Parameters, Future Seismicity, And The Final Model – Petersen (25 min)

· Discussion (30 min)

Lunch Special Lunch Presentation: Can Stress Measurements Help Determine Whether Induced Seismicity Is likely? (30 min)

Part 3: Other Methods & Government Panel · One Application Of A Traffic Light System – Holland (20 min)

· Another Option – Operational Earthquake Forecasting – Field (20 min)

· Discussion (20 min)

· Government Agency Panel And Discussion – (1 hour)

15 min break

Industry Panel and Wrap-up · Industry panel (1 hour)

· Wrap-up, Next Steps, & Comments (30 min)

8:00-9:15

9:30-11:00

11:15-12:30

12:30-1:45

1:45-3:45

4:00-5:30

National Seismic Hazard Workshop on Induced SeismicityTuesday, November 18, 2014

AM

PM

OKLAHOMA GEOLOGICAL SURVEY

96

97

98

99

ProfessionalPresentationswithAbstracts

Chang,J.(2015)Semi-InfiniteGeologyModelingAlgorithm(SIGMA):AModularApproach

to3DGravity[Abstract86140],AmericanGeophysicalUnionFallMeeting,December17,

2015.

Darold,A.P.,Holland,A.,Gibson,A.(2014),AnalysisofSeismicityCoincidentwithHydrau-

licFracturingofaWellinSouthernOklahoma,inAmer.Geophys.UnionFallMeeting,Poster,SanFrancisco,CA.

Darold,A.P.andA.A.Holland(2015),AnalysisofSeismicityCoincidentwithHydraulicFrac-

turingofaWellinSouthwestOklahoma,SeismologicalSocietyofAmericaMeeting,Pasa-

denaCA,April20-23,2015.

Darold,A.P.andA.A.Holland(2015),AnalysisofSeismicityCoincidentwithHydraulicFrac-

turingofaWellinSouthwestOklahoma,GeologicalSocietyofAmericaSouth-CentralSec-

tionMeeting,StillwaterOK,March19-20,2015.PDFDownload

Holland,A.A.(2014,PotentialCaseofInducedSeismicityfromaWaterDisposalWellin

South-CentralOklahoma,Seismol.Res.Lett.,85(2),452.

Holland,A.A.(2014),InducedSeismicityfromFluidInjectionandDraftBestPractices,

GroundWaterProtectionCouncilUICConference,NewOrleans,LA,Jan.21-23,2014.

Holland,A.A.(2014),RecentEarthquakesinOklahomaandtheMid-continent:Significance

andPotentialforInducedSeismicity,21stIntegratedPetroleumEnvironmentalConsortium

Conference,Houston,TX,Oct.13-14,2014.

Holland,A.A.(2014),Inducedseismicity“UnknownKnowns”:theroleofstressandother

difficulttomeasureparametersofthesubsurface,NationalResearchCouncilJointMeeting

oftheCommitteeonEarthResourcesandCommitteeonGeologicalandGeotechnicalEngi-

neering,Oct.23,2014.

Holland,A.A.,andA.P.Darold(2014),PotentialCaseofInducedSeismicityfromaWater

DisposalWellinSouth-CentralOklahoma,inGSASouthCentralSection,edited,Geol.Soc.Amer.,Fayetteville,AR.

Holland,A.A,andA.P.Darold(2014),Considerationsindisposalwellsitingandopera-

tions:relativehazardandidentificationofinjection-inducedseismicityusingregionalor

localseismicmonitoring,SPE/SEG/ARMAInjectionInducedSeismicityWorkshop,Banff,

Canada,Sep.15-18,2014.

Holland,A.A.andA.P.Darold(2015),Areearthquakestriggeredbyhydraulicfracturing

morecommonthanpreviouslyrecognized?,GeologicalSocietyofAmericaSouthCentral

SectionMeeting,StillwaterOK,March19-20,2015.PDFDownload

Holland,A.A.andA.P.Darold(2015),Areearthquakestriggeredbyhydraulicfracturing

morecommonthanpreviouslyrecognized?,SeismologicalSocietyofAmericaMeeting,

PasedenaCA,April20-23,2015.

HollandA.A.,andG.R.Keller(2015)IndustryContributionstotheOklahomaFaultData-

baseAAPGMid-ContinentSectionMeeting,TulsaOKOct.6-8,2015

100

Holland,A.,G.R.Keller,A.Darold,K.Murray,andS.Holloway(2014),MultidisciplinaryAp-

proachtoIdentifyandMitigatetheHazardfromInducedSeismicityinOklahoma,inAmer.Geophys.UnionFallMeeting,SanFrancisco,CA.

Keller,G.R.,(2015)TheRoleofRiftingintheTectonicEvolutionoftheOklahomaRegion

(2015),GeologicalSocietyofAmericaSouth-CentralSectionMeeting,StillwaterOK,March

19-20,2015.

S.MarshandA.A.Holland,(2015)ComprehensiveFaultDatabaseandInterpretedFaultMapforOklahoma,AAPGMid-ContinentSectionMeeting,TulsaOKOct.6-8,2015

KevinCrainandJeffersonChangpresentedProjectworkonCrustalScaleTomography

(Task8)atanAGUpotentialfieldsworkshopinKeystone,ColoradoinAugust2015.Links

toabstractsforthepresentationsarelistedbelow.

J.C.ChangandK.D.Crain:

https://agu.confex.com/agu/seg15/webprogram/Paper38018.html

K.D.Crain:https://agu.confex.com/agu/seg15/webprogram/Paper38020.html

https://agu.confex.com/agu/seg15/webprogram/Paper38027.html

OnOctober19,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheSocietyforExplorationGeophysicistsAnnualMeetinginDallasTX.

OtherPresentationsandInvitedTalks

AustinHollandwasaninvitedspeakerataNationalResearchCounciljointstandingcom-

mitteemeetingonOctober23,2014onthetopicof“CriticalIssuesintheSubsurface:Using

FieldObservatoriesandDatatoAdvanceUnderstandingofRockBehavior".

AustinHollandwasaninvitedspeakeratabriefingaboutinducedseismicityconvenedby

theU.S.DepartmentofEnergyinOctober2014.

TheprojectteamhadasignificantpresenceattheDecember2014AmericanGeophysical

UnionFallMeetinginSanFrancisco,California.Fourrelatedabstractsincludedinvestiga-

torsontheproject(Daroldetal.,2014,Hollandetal.,2014,Llenosetal.,2014,Majeretal.,2014).ThepresentationbyHollandetal.(2014)wasanintroductiontoboththisRPSEAprojectandotherrelatedeffortsunderwayinOklahoma.

RandyKellergaveatalkonOklahomaearthquakesandtheirpossiblerelationshipstooil

andgasactivitytoaprofessionalengineeringgroupwhoearnedContinuingEducation

Credits(CEUs)fortheirattendanceinSeptember2015

AustinHollandpresentedtheOklahomafaultdatadatabasetotheStanfordConsortiumon

InducedandTriggeredSeismicity(SCITS)inFebruary2015,includinglessonslearnedfrom

theindustrycontributionoffaultdataforthedatabaseassimilareffortsarebeingconsid-

eredelsewhere.

AustinHollandpresentedattheIEAGHGMonitoringNetworkMeetinginBerkeley,CAin

June2015withatalktitled“StrategyforMonitoringLargeRegionsofFluidInjectionand

InducedSeismicity:Oklahoma’sExperience”.

101

KyleMurraymadethefollowingpresentationsinAugust2015:

Aug14,2015Chicago,IL:NationalAssociationofInsuranceCommissioners(NAIC)Center

forInsuranceandPolicyResearch(CIPR)Event–OralPresentationtitledStateoftheScience:TriggeredSeismicityinOklahoma.

Aug15,2015Chicago,IL:NationalAssociationofInsuranceCommissioners(NAIC)

EarthquakeStudyGroupMeeting–OralPresentationtitledOverviewofEarthquakeActiv-ityintheContiguousStates.

Aug27,2015Woodward,OK:WaterTransfer,TreatmentandReuseWorkshopwith

SustainingOklahoma’sEnergyResources(SOER)–OralPresentationtitledWaterUseandPermittinginOklahomaProducedWater,UICandSWD.

OnSeptember10,2015,JeremyBoakpresentedadiscussionofthecurrentseismicactivity

totheHarvardClubofOklahomaCity

OnSeptember16,2015,JeremyBoakpresentedadiscussionofInducedSeismicityand

OklahomaEarthquakestotheOklahomaCityGeologicalSociety.

OnOctober7,2015,JeremyBoakpresentedadiscussionofInducedSeismicityandOkla-

homaEarthquakestotheSocietyofIndependentPetroleumEarthScientists.

OnOctober15,2015,JeremyBoakpresentedadiscussionofInducedSeismicityandOkla-

homaEarthquakestoaconferenceofNobleCountyAssessors.

OnJanuary20,2016,JeremyBoakpresentedadiscussionofinducedseismicityinOkla-

homatotheConsumerEnergyAllianceStateoftheEnergyIndustryRoundtableinOkla-

homaCity,

OnJanuary27,2016,JeremyBoakpresentedadiscussionofinducedseismicityinOkla-

homatotheOklahomaAggregatesAssociationannualmeetinginNorman.

OnFebruary11,2016,JeremyBoakpresenteddiscussionsofinducedseismicityinOkla-

homatotheOklahomaCityRotaryClub,TheTulsaGeophysicalSociety,andtheArdmore

GeologicalSociety.

OnFebruary16,2016,JeremyBoakpresentedadiscussionofinducedseismicityinOkla-

homatotheOklahomaStructuralEngineeringAssociationandtotheSac&FoxNation.

OnMarch3,2016,JeremyBoakpresentedatalkonInducedOklahomaSeismicitytothe

RockyMountainAssociationofGeologists/DenverGeophysicalSociety3-DSeismicSympo-

siuminDenver.

OnMarch7,2016,JeremyBoakpresentedatalkonInducedSeismicityinOklahomatothe

KiwanisClubofOklahomaCity.

OnMarch23,2016,JeremyBoakpresentedatalkonInducedSeismicityinOklahomato

theNormanBoardofRealtors.

OnMarch29,2016,JeremyBoakpresentedatalkonInducedSeismicityinOklahomato

theSEG/SPE(SocietyofExplorationGeophysicists/SocietyofPetroleumEngineers)Work-

shoponInducedSeismicityinFortWorth(March28-30)

OnApril5,2016,JeremyBoakpresentedatalkonOklahomaSeismicitytotheAssociation

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ofEnergyServiceCompaniesinOklahomaCityandtotheSpringConferenceoftheOkla-

homaStructuralEngineeringAssociation.

OnApril13,2016,JeremyBoakpresentedatalkonOklahomaSeismicitytotheTulsa

AssociationofLeaseandTitleAnalystsofTulsa,Oklahoma.

OnMay2,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahomaEarth-

quakestotheNormanLionsClub,Norman,Oklahoma.

OnMay6,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahomaEarth-

quakestotheGeographicInformationCouncilofOklahoma,inOklahomaCity.

OnMay9,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahomaEarth-

quakestotheGeophysicalSocietyofOklahomaCity,inOklahomaCity.

OnMay10,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheFortuneClub,inOklahomaCity.

OnMay19,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheNorthTexasGeologicalSocietyinWichitaFallsTX.

OnJune21,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheUnconventionalResourcesGroupoftheEnergyMineralsDivision,

AmericanAssociationofPetroleumGeologistsinCalgary,Alberta.

OnAugust26,2016,JeremyBoakparticipatedinapaneldiscussiononInducedSeismicity

andOklahomaEarthquakesattheOklahomaSchoolBoardsAssociationconferenceinOkla-

homaCity.

OnSeptember2,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheDepartmentofGeologicalSciencesatOklahomaStateUniversityin

Stillwater,OK.

OnSeptember7,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakesatanAmericanChemicalSocietyChemistryCaféinTulsaOklahomaaspartof

apaneldiscussion.

OnSeptember14,2016,JeremyBoakparticipatedinapaneldiscussiononInducedSeis-

micityandOklahomaEarthquakestotheOklahomaMunicipalLeagueAnnualConference

inOklahomaCity,OK.

OnSeptember15,2016,JeremyBoakpresentedatalkonInducedSeismicityandOkla-

homaEarthquakestotheCouncilofPetroleumAccountantsSocietiesofOklahomainOkla-

homaCity.

OnSeptember20,2016,KyleMurraypresentedatalkonInducedSeismicityandOkla-

homaEarthquakestotheTulsaGeologicalSocietyinTulsaOK.

OnSeptember21,2016,JeremyBoakpresentedatalkonInducedSeismicityandOkla-

homaEarthquakestotheOklahomaCommercialRealEstateForumonEarthquakesin

OklahomaCity.

OnOctober11,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheOklahomaIndependentPetroleumAssociationWildcatterWednesday

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inOklahomaCity.

OnOctober26,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheOklahomaCorporationCommissionOilandGasInstituteinTulsaOK.

OnOctober26,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheU.S.AssociationofEnergyEconomistsAnnualMeetingWorkshopon

InducedSeismicityinTulsa.

OnOctober27,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

Earthquakestothe5thAnnualProducedWaterQualityRecyclingandReuseCongressin

DenverCO.

OnNovember1,2016,JeremyBoakpresentedatalkonInducedSeismicityandOklahoma

EarthquakestotheNormanLionsClubinNorman.

IndustryInteractions

DuringFall2014,ProjectstaffinteractedwithNewDominion,whichprovidedasignificant

costshareforourproject.TheyaresharingideasaboutthecausesofOklahomaseismicity,

andwediscussedthedatathattheyplantoprovideaspartoftheircostsharecommitment.

OnAugust27,2015,andDecember2,2015,JeremyBoakattendedtheSeismicityWorking

GroupMeetingoftheOklahomaIndependentPetroleumAssociation,anddiscusseddata

needsfromtheindustryforevaluationofinducedseismicity.

OnNovember20,2015,JeremyBoaksatonapaneldiscussingseismicityandwastewater

injectionattheannualconferenceoftheOklahomaOilandGasAssociation

JeremyBoakmetwithJulieShemetaofMEQGeo,anindustryconsultantduringtheweek

beforeChristmas2015.

OnFebruary5,2016,JeremyBoakandKevinCrainmetwithChesapeakeEnergytore-

viewseismicdata.

OnMarch2,2016,RPSEAteammembersparticipatedinameetingwithExxonMobiland

XTOpersonnelregardingtheirassessmentofpotentiallyinducedseismicityinTexas,and

onariskassessmenttoolbeingdevelopedforinjectionwells.

GovernmentInteractions

JeremyBoakattendedmeetingsoftheGovernor’sCoordinatingCouncilonSeismicityin

OklahomaCityonSeptember8,2015,October7,2015,May23,2016,July18,2016,August

23,2016,andNovember2,2016.

JeremyBoak,andJeffersonChangattendedameetingoftheGovernor’sCoordinating

CouncilonSeismicityonApril19,2016,August23,2016.

OnJanuary19,2016,JeremyBoakandKyleMurrayattendedtheJanuarymeetingofthe

Governor’sCoordinatingCouncilonSeismicityinOklahomaCity.

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OnFebruary16,2016,OGSstaffmembersattendedtheFebruarymeetingoftheGover-

nor’sCoordinatingCouncilonSeismicityinOklahomaCity

OnMarch21,2016,JeremyBoak,JeffersonChang,andKyleMurrayalsoattendedthe

MarchmeetingoftheGovernor’sCoordinatingCouncilonSeismicity.BothMurrayand

Boakwereinvitedspeakers.

OnMarch25,2016,OGSstaffmembersdiscussedtheupcomingreleaseoftheU.S.

GeologicalSurvey’sone-yearseismichazardassessmentoftheUnitedStates,which

showedbothnaturalandinducedseismichazardforthefirsttime,andhighlightednorth

centralOklahomaasanareawithsignificantriskofdamage.

JeremyBoakattendedtheSecretaryofEnergyandEnvironment’smonthlyDirector’s

meetingOnSeptember14,2015,October19,2015,November30,2015,February22,2016,

March21,2016,April25,2016,May31,2016,July25,2016,October10,2016.

TheOGSseismologyteammetwiththeOklahomaCorporationCommission’sOilandGas

DivisioninNormanonTuesday,October15,2015,onDecember15,2015,February1,

2016,April18,2016,June10,2016,September27,2016,October11,2016.

OnOctober30,2015,JeremyBoakpresentedatalkdiscussingseismicityandwastewater

injectiontoanInterimStudyGroupoftheOklahomalegislature.

OnNovember10,2015,JeremyBoakjoinedapaneldiscussingseismicityandwastewater

injectionattheOklahomaGovernor’sEnergyConference

JeremyBoakattendedmeetingsonseismichazardevaluationattheOklahomaDepart-

mentofTransportationonDecember8,2015,April4,2016,May16,2016.

JeremyBoakattendedthefallliaisonmeetingoftheAssociationofAmericanStateGeolo-

gistsinWashington,DC,September27-30,2015,andmetwithpersonnelfromUSGS,

GeologicalSocietyofAmerica,NationalMiningAssociation,TheNationalAcademies,anda

DOEundersecretary,aswellasstaffofseveralCongressionalCommittees.

USGS

JeremyBoakmetwithagroupattheUSGSNationalEarthquakeInformationCenterdur-

ingtheweekbeforeChristmas.

JeremyBoakmetwithRobertWilliamsoftheUSGSNationalEarthquakeInformationCen-

terJune7,2016.

TheOGSseismologyteammetwithagroupofU.S.GeologicalSurveyandCongressional

staffonJune28,2016.

JeremyBoak,JeffersonChang,andKyleMurraymetwithUSGSandOklahomaCorpora-

tionCommissionstafftodiscussseismicityinOklahomaonJune30,2016.

JeremyBoak,NoorulanGhouse,andJeffersionChangvisitedtheUSGSNationalEarth-

quakeInformationCenteronJuly22,2106todiscussanalysisofseismologicdata.

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RPSEAMeetings

OnSeptember17,2015andMarch9,2016,JeremyBoakgaveaWebexupdateonthe

RPSEAProjecttoRPSEA,NETLandDOEpersonnel.

OnNovember4,2015,JeremyBoakpresentedadiscussionofthecurrentseismicactivity

toaRPSEATechnologyTransferworkshopinHouston,Texas,alongwithRandyKeller,

whodiscussedthelargertectonicpictureofOklahomaseismicity.

JeremyBoakpresentedatalkontheRPSEAProjectandInducedSeismicityinOklahomaat

theBestofRPSEAconferenceinGalvestonTX,August31,2016.