IS-01

Borehole Seismology

Prof. Dr. Marco Bohnhoff Kashiwazaki, Nov7 2012

Borehole Seismology: Fundamentals and Applications

Prof. Dr. Marco Bohnhoff

Helmholtz-Centre Potsdam GFZ and Free University Berlin

Contact: [email protected]

Borehole Seismology


IntroductiontoBoreholeSeismology

Whydownhole?ChallengesandStateoftheArt

CaseStudiesofDownholePassiveSeismicMonitoring

InducedseismicityattheBerlingeothermalfieldinElSalvadorSeismicmonitoringofCO2 storageandleakageatthePennWestEORpilot(CA)

ConcludingRemarks

PresentationOutline

Borehole Seismology


(inalphabeticalorder,coauthorsofreferredownpaper)

Bulut,Fatih(GFZPotsdam)Chalaturnyk,Rick(UAlberta,CA)Dresen,Georg(GFZPotsdam)Ellsworth,Bill(USGSMenloPark)Ito,Hisao(JAMSTECTokyo)Kwiatek,Grzegorz(GFZPotsdam)Martinez,Patricia(GFZPotsdam)Zoback,Mark(StanfordU)

withcontributionsfrom:

Borehole Seismology


PassiveSeismicMonitoring:Motivation210 12345 67

Earthquakemagnitude(Richterscale)

Magnitude -2 / -1Rupture surface mSlip mm

Magnitude 7+Rupture surface >10 kmSlip m

(reconstruction)

detectthesmallones betterunderstandthelargeones

Borehole Seismology


(Bohnhoffetal.,ILP,2010)

EarthquakeMagnitudeRanges

Length and displacement approx. and appropriate for stress drops of 3 MPa* 1 Aki is defined as 1018 Nm and named after Keiiti Aki who pioneered the use of seismic moment in theory and practice** the term microearthquake traditionally refers to M

Borehole Seismology


Drillingisexpensive(inoil/gasindustrydrillingcostsare>10timesthecostsforpresitesurveys...).

Drillingisriskyandlogisticallyextremelydifficult.Downhole instrumentsneedtooperateatelevatedpressureandtemperatureconditions.

BUT:Downholeseismicmonitoring...

...allowstomonitoratsubstantiallyreducednoiseconditionstherebyimprovingsignaltonoiseratio,magnitudedetectionthresholdandprecisionofhypocenterdetermination.

...allowstobroadenthefrequencybandoftherecordedwavefieldthroughrecordingalsohigherfrequencycontents.

HOWEVER,challengesinboreholeseismologyareasecuredeploymentofsensors(ensuringgoodcouplingtotheformation),safedatatransmissiontothesurface,formationpressure/temperature/fluids.

WhyGoingDownhole?

Borehole Seismology


CouplingofBoreholeSeismometers

Agoodcouplingofthesensorstothecasing/formationisessentialtogeneratereasonablygooddataquality.

Thiscanbeachievedthrough:

Sandbackfillingsensorsatthebaseoftheborehole(temporaryorpermanent)

Cementingsensorsinboreholeorbehindcasing(permanent)

Mechanicalcouplingofthesensortotheboreholewallorcasing(mostlytemporary)

Temporarydeploymentinanopenholesetting

Borehole Seismology


CouplingofBoreholeSeismometers

Agoodcouplingofthesensorstotheformationisessentialtogenerategooddataquality

Canbeachievedthrough:

Sandingsensorsatboreholebase(temporaryorpermanent)

Cementingsensorsinboreholeorbehindcasing(permament)

mechanicalcouplingtoborewallorcasing(mostlytemporary)

Examplefroma2x83Cboreholegeophonearray

Deploymentofaboreholegeophone(ESGLtd.)

Borehole Seismology


OrientationofBoreholeSeismometers Nodirectinfluenceonorientationofsensorsinboreholealthoughessential. Sensorsneedtobeverticallyorientedwithinafewdegree(or:gimbledsensor). Horizontalorientationcanbedeterminedthroughcheckshots(providesalso.feedbackonsensorquality,couplingandformationvelocity).

Array1Array2

= injection = seismic sensor = well trajectory

checkshots

(Bohnhoffetal.,IJGGC,2010)

Borehole Seismology


OrientationofBoreholeSeismometers Nodirectinfluenceonorientationofsensorsinboreholealthoughessential. Sensorsneedtobeverticallyorientedwithinafewdegree(or:gimbledsensor). Horizontalorientationcanbedeterminedthroughcheckshots(providesalso.feedbackonsensorquality,couplingandformationvelocity).

Array2

Array1

Vp/Vs=1.84(Vp=4.8km/s,Vs=2.6km/s)

PWaves

BoreholeSeismograms Wadatidiagram

(quasi)SWaves

(Bohnhoffetal.,IJGGC,2010)

Borehole Seismology


Atypicalfrequencybandofaseismicsurfacestationextendsupto~100Hz Higherfrequenciesarenotseenduetoattenuationintheshallowformation

ObtainingHighFrequencySignals3

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500HzData:Filtered1100Hz,2s

Borehole Seismology


Samedata butbandpassfilteredabove100Hzdemonstratingthebenefitof conditionsallowingrecordalsohigherfrequencycontentsofthe seismicwavefield.

ObtainingHighFrequencySignals3

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500HzData:Filtered100240Hz,2s

Borehole Seismology


SignalToNoiseImprovementWithDepth

(P.Malin,pers.comm.)

Qualityofseismicrecordingstoalargeextentisdefined

bythenoiseconditionsatthesensor.

Noiseconditionsimprovesubstantiallywithdepth.

Involvingdrillingcostsseveralhundredsofmetersrepresentanoptimumforthereturnoninvestmentindownholepassiveseismicmonitoring.

Borehole Seismology


DownholeSeismologyinFundamentalResearch Sincefirstseismicnetworksin1910/20ssystematicdensification(regional/global).TodayMc 2inwesternUS,Japan,westernEurope.

1986:InstallationoftheParkfieldHighResolutionSeismicNetwork(HRSN):Depthofsensors65550m(mostly250m),datasampledat250Hz.

HRSNParkfield

Borehole Seismology


(Rutledgeetal.,BSSA,1998)

Mostlyshorttermdeploymentsfordownholeseismicmonitoringofreservoirstimulation(hydrocarbon,geothermal,shalegasreservoirs).

Usuallyseismometerstringsinoneorseveralmonitoringwells closetoreservoir.

DownholeSeismicMonitoringinIndustry

(Kwiateketal.,ActaGeophys.,2010)

Borehole Seismology


(Okadaetal.,EPS,2004)

1995 2003

BoreholeSeismologyinJapan:StationDistribution Highsensitivityboreholestations,typicallyat100mdepth

Borehole Seismology


Casestudy1:

MonitoringInducedSeismicityintheBerlinGeothermalField,ElSalvador

Borehole Seismology


1km

BerlinGeothermalField:Location LocatedontheflancsofdormantvolcanoCerroTecapa. 8productionwellsand10injectionwells(closedfluidcirculation).

Borehole Seismology


S N

Injectionwell

1km

SHmax

BoreholeSeismometerNetwork 12boreholesensors(nat.frequencies1/4,5/5,5/30Hz)sampled 243000Hz. 3stimulationcampaignsof3weekseachat2differentdepthintervals.

Depthsection Mapview

Borehole Seismology


WholedatasetDuringinjectionintoTR8A1km

RelevanceofApplyingstateoftheartProcessingTechniques:RelativeRelocation

ApplicationofhypoDDtechnique(Waldhauser/Ellsworth,2001)totraveltimepicks.

Systematicshiftofhypocenterlocationstowardsthegeothermalfield(wrtinitialabsolutelocations).

Strongclusteringofeventsaroundinjectionwells.

Clearrelationbetweenseismiceventsandstimulation.

(Kwiateketal.,subm.)

Borehole Seismology


1km

Applicationofwaveformcrosscorrelationtechniquetodeterminesignalsimilarityatindividualboreholesensors.

Identificationof9eventfamiliesdisplayingsimilarruptureprocesses.

FocusonseismicityatwellTR8Ainthefollowing(deepbluefamily).

RelevanceofApplyingstateoftheartProcessingTechniques:ClusterAnalysis



Borehole Seismology

SHmax

250m

Wellheadpressure Injectionrate

Spatiotemporaloccurrenceofseismicity Temporalmigrationofseismicityawayfromthereservoirtowardsafaultplane. Abruptincreaseofeventmagnitudesandchangeofmigrationduringshutin.


Borehole Seismology


Initialspectralfittingmethod Afterspectralratiorefinement

RelevanceofApplyingstateoftheartProcessingTechniques:SourceParameters

Determinationofsourceparametersusingarefinedspectralratiotechnique Strongimprovementsonthequalityofsourceparameters(M0,r0,)


Borehole Seismology


Whilegoodqualitydataisaprerequisiteforanystudy,stateoftheartevaluationmethodsareessentialtoobtainoptimumandreliableresults.

Relativerelocationofhypocentersallowstoidentifyasystematicmigrationofeventstowardsandalongmappedfaultplanes,probablyinitiatedbythe

elevateddownhole pressure duringinjection.

Largermagnitudeeventsandseismicityclustersareobservedduringshutinphases.

Seismicityoccursinpreviouslyactiveareasonlyoncetheearliermaximumdownholepressureisexceeded(Kaisereffect).

BerlinGeothermalField:LessonsLearnt

Borehole Seismology


Casestudy2:

DownholepassiveseismicmonitoringofCO2storageandleakageinthePennWestEORpilot

Borehole Seismology


PassiveSeismicMonitoring(PSM)isafrequentlyusedtechniquetostudynaturalandfluidinjectioninducedmicroseismicityalongfaultzonesandinhydrocarbonandgeothermalreservoirs.

MonitoringinducedseismicityintheframeofCO2 storageisstillinitsinfancyandhasnotyetbeenadressedsystematicallydespiteits greatpotential.

WereportonPSMinthePembinaOilFieldtoanalyzeCO2 leakageandtopotentiallycharacterizetheCO2 storagereservoirusinginducedmicroseismicity.

PassiveSeismicMonitoringofCO2 Storage

Borehole Seismology


ThePennWestCO2 InjectionProject Location:PembinaOilField,westernCanada;EORProject. Monitoringwellat350mdistancefrominjectorwell(I1)

butonly35mawayfromproducerwellP1.

P1 P4

Monitoringwell

P6

P2 P5P3

I1 I2

Injectionwell

Borehole Seismology


8threecomponentgeophones sensorspacing20mat1500to

1640mdepth 24Hznaturalfrequency 1kHzsamplingfrequency

1302m

1500m

1640m

BellyRiver

Wapiabi

Cardium(CO2 reservoir)

Blackstone

Geophone

Pressure/TemperatureFluidsample

Instrumentation

Lithology

z

PennWestDownholeGeophoneArray

Borehole Seismology


Objectives:MicroseismicandLeakageMonitoring

Borehole Seismology


Absenceoftypicalsignaturesofmicroseismiceventsinspectogramsofcontinuousdata

Dominantenergyupto200Hz,clearindicationof50Hzsignalsandmultiples

Noobviouscorrelationbetweenindividualsensors

Usefultooltoquantifysignalqualityofindividualsensors

SpectralAnalysisofWaveformRecordings

Borehole Seismology


SystematicsearchfornoiselevelchangesframingthetimeofaknownCO2leakage(outburstwithinmonitoringwell)

Result:Clearincreaseofthenoiselevelduringrelevanttime.But

AnalysisofNoiseLevelsatIndividualSensors

Borehole Seismology


NoiselevelduringCO2 Accident detected noise level increase is not simultaneous.

Borehole Seismology


Frequencycontent:

Noiseanalysis:

STA/LTA:

Lowfrequencysignals:

Mostlyin[0,50]Hz. Abundantsignalswithenergyupto500Hz. Studyofreliabilityofeachsensor. IdentificationofsignalsrelatedwiththeCO2/CH4

outflow.

Numerouspotentialeventsfoundbutooweaktobefurtheranalyzed.

Observedsignalsnotmatureenoughtoverifyoccurrenceoflowfrequencyeventsduringinjection.

PennWestStudy:LessionsLearntNoevidencefoundforinducedmicroseismiceventsatMw>1.

Borehole Seismology


(Casestudy3):

DownholepassiveseismicmonitoringofnaturalmicroseismicityattheMarmaraSeismicGap,NW

Turkey theGONAFproject.

TalkonThursdaymorninginTechnicalSessionS1:DevelopmentofSeismicObservationinDeepBoreholeanditsApplications

Borehole Seismology


SomeGeneralConclusions

Recentdevelopmentsindownholepassiveseismicmonitoringtechnologyallowtorecordhighqualitydatasetsofmicroseismicitywiththepotentialofaddressingvariousrelevantseismologicaltopics.

CasestudiesfrompassiveseismicmonitoringwerediscussedstressingthatBasicandAppliedSeismologyaregenerallystronglyinterconnectedaddressingsimilartopics.

Futurechallengesinpassiveseismicmonitoringareintensifyingthe(permanent)deploymentofdownholeseismicinstrumentation

ensuringlongtermoperationatimprovednoiseconditions,recordingalsothehigherfrequenciesoftheseismicwavefield.

Borehole Seismology


Thank you for your attention!

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