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PS Processing and Joint Inversion in Junggar Basin, Northwest China

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PS Processing and Joint Inversion in Junggar Basin, Northwest Chinain,ps,PS,and,Joint,China,joint,Basin

    PS Processing and Joint Inversion in

    Junggar Basin, Northwest China

    20107月岩性油气藏

    LITH0L0GICRESERVOIRSCEG会议专刊

    ?

    地震处理?

    DelineatingOilinSandReservoirsbyHighReso

    andJointInversioninJunggarBasin,N

    lutionPPJ/PSProcessing

    orthwestChina

    XiaoguiMiao,WangPu,ShenLiang.,ZhangSihai.,DangYufang,LouBing

    (1.CGGVeritas;2.ResearchInstituteofExplorationandDevelopment,XinjiangOCompany,PetroChina)

    Abstract:DramaticlaterallithologicalvariationsinthefluvialsedimentsinChepaizi,JunggarBasinofNorthwest

    China.haveposedpotentialchallengesanddifficultiestodistinguishbetweentrueandfalse"brightspots"inoil-

    bearingsandreservoirs.Ahighresolutionmulti

    componentseismicsurveyandjointprestackPPandPSinversion

    conductedrecentlyinthearea,haveprovidedaneffectivetechniquetosolvetheproblemandsuccessfullydelineatethe

    characteristicsofthereservoir,duetotheadditionalbenefitsobtainedfromthedifferentreflectionresponsetolithology

    andfluidcontentofshearwaves,andtheircapabilityofresolvingthinlayers.Surfaceconsistentamplitudeand

    resolutionpreservingprocessinghasproducedhighqualityprestackPPandPSmigratedgathersandstacksfor

extractingseismicattributes.ApplicationofthejointprestackPPandPSinversionhasdemon

    stratedhigherfluidfactors

    andlowerV./Vratioatthelocationofoil

    bearingsandscomparedwiththedrysandsinthisarea.Fromthecorrelation

    betweentheinversionandtheexistingwelldata,itisconcludedthatapromisingexplorationte

    chnology,suchasthe

    highresolutionmulti

    componentAVO,canreducedrillingrisksandprovidemoreaccuratereservoircharacterizati

    on

    forseismicexploration.

    Keywords:highresolution;sandreservoir;PPSjointinversion;JunggarBasin 中图分类号:P631.4文献标识码:A

    Introduction

    TheChepaiziareaislocatedinZunggarbasin,North

    westChina.In2006,anexplorationwellChe89wasdrilled, whichturnedouttobehighlyproductive,producingfrom theShawanformationgroupofthePliocene.Consequent

    ly,morewellshavebeendriHed,butfiveoutofeightwells weredry,eventhoughthereflectioncharactersatthese wellslookedlikethesocalled"brightspots,''similarto Che89.Ithasbeenbelievedthattheextremelateral lithologicalvariationduetothefluvialsedimentslcadto thesediculties.Tounde~tandbetterthecharacteroftl1e reservoir,ahighresolution2D3Cseismiclinewasacqui. red.Itwentthroughthetwotestwells,Che89(goodpro

    ducer)andChe97(drywel1),usingDSU3digitalsensor units,basedonMEMsaccelerometertechnology.The surveywasacquiredwithasamplerateof1msandabin sizeof5mandanaveragefoldof50.Forbetterreservoir characterization,highresolutiondataprocessinganda

    jointprestackPPandPSinversionhavebeenperformed, theresultsofwhicharepresentedinthispaper. Theoryandmethod

    ConventionalAVOinversionwithasinglemodeP wavetriestoinvertthreeunknowns,Vp,Vanddensity fromtwoseismicattributesPwavegradientandinter-

    cepttime.Thiscausesuncertaintiesintheinversion.The iointPPandPSinversionhasstabilizedtheproblemby introducingPSgradients(Russelletal,2006).However, inpractice.thenoisejnbothPPandPSgradientsalso causessomedicuhiesintheinversion.Garottaeta1. (2002)proposedadualinversionscheme,whichusesthe verticalV./VratiofromPPandPStraveltimeregistration combinedwithPPandPSAVOattributesintheelastic inversion.ThemethodhasbeensuccessfullyusedinOBC datafromNorthSea.aswellasin1anddatafromDaqing areaofChina(Sheneta1.2008).Theinversioninvolves mainlytwosteps.thefirststepistoextractAV0attribute sections(Rppinterceptsection,Gppgradientsection), derivedfromthemigratedPwavegathers,andthePS

    Abouttheautho:XiaoguiMiao,CGGVeritas.Email:zhengpeng.kang@pdgm.COB 岩性油气藏2010

    gradientsectionfromthemigratedPS-wavegathers.Assu. minga1Delasticisotropicearthmodel,asimulated annealingtechniqueisusedduringtheinversiontofinda globalminimainthiscomplexoptimizationandthento computetheelasticparametersforthetargetareainthe secondstep.

    Datapreprocessing

    Thethreecomponentdataareofgoodquality.Even

    thoughthereisstrongcoherentnoise,andsomerandom noise,thespectralanalysisofvalidsignalsfortheoriginal shotsdemonstratedbroadfrequencybandwidthsforboth P-waves(upto200Hz)andPS-waves(upto100nz). Thedominantfrequenciesarearound70——90HzfortheP

    wavesand3540Hzf0rPSwaves.Itprovidesagoodbasis forustoperformhighresolutionPPandPSinversion.The keystepsinvolvedinpre-processingincludegoodnoise attenuationforbroadbanddata,shearwavestatics,surface consistentamplitudecorrection,surfaceconsistentdecon

    volutionandstatics,andprestacktimemigration. Figure1showsacomparisonoftheP——waveseismic

    databeforeandafterdec0nv0luti0n.Itisobviousthat deconvoluti0nhasenhancedseismicresolution.morethin layerscanberesolvedandthecontinuityeventshasbeen improved.ToenhancetheseismicresolutionforPPand Beforedeconvolution

    Afterdeconvolution

    Fig.1Pwavesectionsbefore(upper)andafter(1ower) surfaceconsistentdeconvOIu6on.Resolutionhasbeen enhancedbydeconvolution

    PSdata,higherordermoveoutcorrectionswerealsoper- formedduringthePPandPSprestacktimemigrations,so thatthesmearingcausedbyanflattenedlongoffsetdata

    couldbereduced.Figure2showsthefinalPPandPS prestacktimemigratedsectionsandtheircorresponding spectra.ThePSsectionhasbeensqueezedtoPPtimeby usingthevertiealV/VratioobtainedfromthePPandPS registration.

    Fig.2PPandPSwaveprestacktimemigrationsections

    andspectra:upper:PPsection;lower:PSsection PSdatamatchingandeventregistration

    ThemostimportantstepisregistrationofPwavereflec- tioneventswit}Itheirequivalentreflectionsonthecon

    vertedwavedata.Sincethetwodatahavedifferentfre. quencybands,wehavedesignedamatchingfilterwhich matchestheamplitudespectraofthePwavestotheamp

    litudespectraofthePSwaves,withoutchangingtheirphase spectrapriortothecorrelationoftheevents.Thesynthe

    ticseismictracesarecreatedbasedonP-wavesoniclog informationusingwaveletsderivedfromthePSTMsec. tionsforbothPandPSwaves.Itisnoticedthatwhen calibratingsurfacethePSwaveseismicsectionwithwell logs,an180.phaserotationisneeded.Forbothwells,it isobviousthatthesyntheticseismogramscorrelatewell CEG会议专刊

    XiaoguiMia0,eta1:Delineating0ilinSandReservoirsbyHighResolutionPP,PSProcessing

    andJoint1

    InversioninJunggarBasin,NorthwestChina一旦

    withtheprestacktimemigratedsectionsforbothPand PSwavesasseeninFigure3and4.

    Fig.3Thewelllogcurves,computedPPimpedancesand syntheticseismograms(bluetraces)comparedwithPwave

    surfaceseismic(redandblacktraces)forthemeUs Che89(1eft)andChe97(right)

    Fig.4ThecomputedPSimpedancesfromlogcurvesand syntheticseismograms(bluetraces)comparedwithsurface PSseismicsectionatwelllocations(blacktraces).The surfacePSwavesectionhasan180.phaserotationand isplottedinred

    ThenthePPandPSeventregistrationiscarriedout withthematchedP..waveandPS-wavesectionsforthe

    targetzone,whichisatadepthof9002000mandlsin

    PPtime.ThreehorizonswerepickedforbothPandPS waves.TheinitialGamma(V./Vratio)obtainedfromev- entsregistrationisusedtosqueezePSsectiontoPPtime. Afterseveraliterationstoadjustthehorizons,thePPand PSsectionsmatchverywell(SeeFigure5),andtheupda- tedGammawillbeusedasareferencemodelinthejoint inversion.

    Beforethejointinversion,acomparisonanalysiswas conducted.Table1isthecomparisonofthePwave,the matchedPwaveandtheold3DP-wavesectionsatthe targetformationforbothwells.Atthelocationofwell Fig.5TheeffectofPP/PSeventregistrationatCDP180~. TheP-wavesectionisplottedontheleft;thePSsection isplottedontheright.Aftereventregistration,horizons canbetracedcontinuouslyonbothsections

    Che97,similarbrightspotsbetweenthematchedP-wave andtheold3DPwavesections,whichhavealowerfre

    quencybandwidth,areobserved.ButintheoriginalP

    wavesectionwithoutmatching,thebrightspotdoesnot exist.Itisreplacedbymultipleformationsinthehigh resolutionprocessingresult(seerable1P-wavesection atChe97).Table2isacomparisonoftheP-wave,the matchedPwaveandthePSwavesectionsatthetarget

    zoneforbothwebs.AtwellChe89thesamebrightspotis showninbothoriginalandmatchedP-wavesections,but itdisappearsinthePSwavesection,whichimlpliesthat thebrightspotintheP-wavesectionisduetoahydro-

carbonexistence.

    Table1AcomparisonofthePP,matchedPPtothePS spectraandtheold3DPwavesectionsinthetarget formationforbothwells

    Table2AcomparisonofthePP,thematchedPPtothe PSspectrasectionsandthePSsectionsinthetarget formationforbothwells

    62岩性油气藏2010

    ButatwellChe97.thematchedP-wavesectionlooks almostthesameasthePSwavesection,whichmeans

    thatthereflectioncharacterisrelatedtolithologyand,not thefluidcontent.Thismaybeanindicatoroftheexistence ofhydrocarbonsincePSwavesarenotsensitivetofluid contents.

    PPandPSiointinversion

    TheinputstothePP/PSiointinversionareAVO

    attributes:theP-wavegradient,Rpp,andintercepttime, GppandthePSwavegradient,Gps.ThereferenceVp/V

    ratiomodelfromtheeventregistrationisalsousedasthe initialmodelfortheiointinversion.Thesimulatedannea- lingschemewasstartedatatemperatureof900,andthe errortolerancewassetto0.0001forprogramtermination. Aftertheiointinversion,wegotaninvertedVp/Vratio, whichisshowedinFigure6,thefluidfactors(seeFigure WeUCrl97

    7)andPoissonratios.Correlationwiththelogcurves andtheinversionresults.distributionofthearysandswith .

    /Vratiovaluesaround2.1aredisplayedasyellowto redcolors;theshalelayerswithVp/Vratiovaluesaround

    2.6aredisplayedasbluetopurplecolors(seeFigure6). Atwel1Che89ofthetargetformation,theVD/Vratio valuesdemonstrateastronganomalywithvaluesaround 1.7.whicharedisplayedbygreencolorinFigure6.At weUChe97.noanyanomalyinthetargetformationis 0bserred.Therefore,accordingtotheinversionresult, hydrocarbons,drysandsandshalescanbediscriminated clearlybyV./Vratiovalues.ThefluidfactorsandPois

    son'sratiowerecalculatedfromtheinvertedVp/Vratio. Bothofthemalsoindicateananomalyinthesaturated san&toneatwellChe89location.Figure7showsthe nuidfactorsforthetargetzone,whichalsoillustratesa highervalueoffluidcontentatwellChe89,butlackof WeUC89

    Fig.6TheinvertedVplV~ratio,gamma,atwellsChe89(right)andwellChe97(1eft)

    Fig.7Theinvertednuidfact0rsatthetargetzone.WellChe97isontheleftandwellChe89isonri

    ght

    anomalyatwellChe97

    Discussion

    Asmentionedearlier,withhighresolutionprocessing intheP-wavesectionexactlybelowthe"false"brightspot atwellChe97,tworeflectionsayeobserved(seeFigure3, indicatedbyaredarrowontheright)insteadofonlyone strongreflectionintheconventionalprocessedsection andthematchedPwavesection.Isitrealgeologically? T0conrn1this,wehavecheckedthewelllogcurvesfor wellChe97andfoundoutthatathinsandlayerexists exactlybelowthe"false"brightspot(seeFigure3,indica? tedbyaredarrowontheleft).Inaddition,byregistration 0fthesyntheticseismogramwiththepetrophysicaldata,

CEG会议专刊

    XiaoguiMiao,etal:DelineatingOilinSandReservoirsbyHighResolutionPP,PSProcessing

    andJoint

    InversioninJunggarBasin,NoahwestChina63

    thethinsandlayerexactlybelowthe"false"brightspotcall beclearlyidentifiedinthesyntheticseismograms,which isalsoconsistentwiththesurfaceseismic.Therefore,itis safetosaythattheP-wavesectionwithhighresolution acquisitionandprocessingdelineatesthedetailedgeolo

    gicalinformationandthefalsebrightspotisrelatedtoa tuningeffectonthepreviouslowresolutionseismicdata. Accordingtothepetroph)rsicalanalysis,theVp/V. ratioofthesaturatedsandstonesnormallychangesfrom 1.6to2.0(displayedingreeninFigure6).Withoutthe dipolesoniclogdataavailableinthesurvey,webuiltan Avefluidreplacementmodel(threephaseswith90~,4oil, 5%gasplus5%water)tosimulatet}leVvariationcaused byexistenceoftheoilandgaswithinthetargetzone.Itis noticedthattheV./Vratiodramaticallydecreasestoless than2.0(1.62.0)withintheoilsandreservoirwhichis quiteconsistentththeassumption.Theoretically,Vwill generallyincreasebutVpwillnotchangetoomuchwithin thesaturatedsandstonesduetodifferentsensitivitiestn porefluidsofthePandshearwaves.Consequently,theVp/ Vratiowilldramaticallydecreaseandresultinamuch lowervaluethanthatisseeninthedrysandformations. Conclusions

    Multi-componenthighresolutionamplitudepreserving processingonChepaizi3Cdatahasresolvedafalsebright spotintotwothinlayersatwellChe97.ThePSsection

alsoshowsdifferentamplitudecharactersfromthePwave

    sectionandlackofafluidfactoranomalyatwellChe89.

    butsimilaramplitudecharactersatwel1Che97.Basedon

    theseinputs,theiointPPPSinversionhassuccessfully

    invefledhighresolutionVp/V.ratios,fluidfactors,and Poissonratios.ThelowVrl/ratiovaluesandlowPoisson's ratioclearlycharacterizedthereservoiratwellChe89, whereasatthelocationofthefalsebrightspotatwell

    Che97,thesecharacteristicswereabsent.

    Acknowledgments

    TheauthorsgreatlyappreciateMr.HuantongLu,

    ZhigangChenandYongLuoofPetroChinaXinjiang,for

    theirvaluableadviceforthiswork.Wealsogreatlyapp-

    reciateMr.DenisMougenotofSercelforhisvaluable

    suggestionsinthesurveydesignandduringtheinver-

    sion,andPierreYveGrangerofCGGVeritasforhishelp

    duringtheinversion.

    References:

    RussellB,HampsonD,HirscheKeta1.2005,Jointsimultaneousinversion 0fPPandPSanglegathers,CREWESresearchreport,vo1.17. GarottaR,P.Y.Granger,H.Dariu.2002,Combinedinterpretation0fPPand PSdataprovidesdirectaccesstoelasticrockproperties:TheLeading Edge,21,532535.

    DariuH,R.Garotta,P.Y.Granger.2003,SimultaneousinversionofPPand PSwaveAVO/AVAdatausingsimulatedarmeahng:73thAnnualIntema- tionalMeeting,SEG'ExpandedAbstracts,120-123.

    HangShen,JunJieLiu,DDenisMougenote,eta1.2008,SEGannualconven- t_ion,PPPSdualinversionappliedto2D-3Cseismicdata:Xushengas field(Daqing,China).

    GarottR,GrangerPY,DariuH.2002,CombinedinterpretationofPPandPS

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