Workshop Analyses.docx

Workshop Analyses.docx

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WorkshopAnalyses

OmniWorkshopSurveyAnalyses

AllanalysesusetheShot-ReceivertracepairsdescribedbyaScriptfromaSurveyoraStreamer.MostanalysesaresuitableforbothsurfaceseismicandVSP（VerticalSeismicProfile）surveys,unlessotherwisenoted.

AllanalysesexcepttheSyntheticAnalysisarecalculatedusingaBinGrid.OutputdataarecalculatedwithineachBinGridcell.

DepthAnalysis

CalculatesanddisplaysStackFold,i.e.thefoldbeforemigration.

ThisanalysisusestwoOmniVelocityfunctions,oneforPvelocityandoneforSvelocity.

Tracesarecalculatedbyray-tracingoveranumberofflatlayersbelowtheSurvey,definedbyatopelevationandanegativeelevationincrement.Tracesarethenbinnedbytheirreflectionpointlocation.Theresultisa3Dvolumeoftracedata,definedbyinlinebinnumber,cross-linebinnumber,andlayerelevation.

TheShotandReceiverelevationattributeisused,whichallowsformodellingVSP,reflectiontomography,orsurfaceseismicinthepresenceofsignificanttopography.

EitherPPorPSreflectionsmaybecalculated.Inthecaseofreflectiontomography,whereitispossibleforboththeShotandReceivertobebelowthereflectinghorizon,theuserisabletoselectonlyreflectionsfrom"upperreflectors","lowerreflectors",orboth.

ForPPreflections,ifboththeShotandReceiverareatthesameelevation,thereflectionpointwillbeatthehorizontalmidpointbetweentheShotandReceiver.However,iftheShotandReceiverareatdifferentelevations,thenthereflectionpointwillmoveclosertowhicheverthestationisclosertothereflectinglayer.

ForPSreflections,thenon-asymptoticreflectionpointiscalculated,takingintoaccounttherelativeelevationsoftheShot,Receiver,andreflector.

Aftercalculation,theusermayselectasubsetoftracesbasedon:

∙Theoffsetofeachtrace,whichisthehorizontaldistancebetweentheShotandtheReceiver.

∙Theazimuthofeachtrace,whichisthedirectionfromtheShottotheReceiver.

∙TheNMOstretchofeachtrace,whichisthepercentagebywhichthetraceisstretchedintimerelativetoazero-offsettrace.

IlluminationAnalysis

Calculatesanddisplaysfoldonacomplexsub-surfacereflectinghorizon.Thehorizonisasingle-valuedfunctionofEastingandNorthing.Thatis,itmayexhibitsignificanttopographybutmaynot"foldback'uponitself.

ThisanalysisuseseitheranOmniTargetModel,orOmni3DRayModelasinput,todescribethegeology.

Tracesarecalculatedbyusingoneof3ray-tracingoptions:

1.StackFold,asdescribedintheDepthAnalysis.However,inthiscasethetracedataiscalculatedonlyatthedepthsatwhichthereflectinghorizonintersectstheDepthAnalysisvolume.ThereflectinghorizonisdefinedbyanOmniTargetModel.

2.SimpleMigratedFoldonanOmniTargetModelhorizon.Withinthisoption,2ray-tracingmethodsarepossible:

▪Curvedray.InthiscaseboththeShotandReceiverareassumedtobeatzeroelevation,buttheraypathsarecurvedbasedonthevelocitymodelasdescribedintheOmniTargetModel.

▪StraightRay.InthiscasetheShotandReceiverelevationsattributesareused,buttheraypathsarestraight.I.e.thevelocitymodelintheOmniTargetModelisignoredandaconstantvelocityisassumed.ThismethodisnotsuitableforVSPsurveys.

3.ComplexMigratedFoldonanOmni3DRayModel.Thisisfull3Dcurvedraytracing.BothShotandReceiverelevationsareused,andraysarecurvedthroughthevelocitymodeldescribedwithintheOmni3DRayModel.ThereflectinghorizonischosenfromthehorizonsdefinedwithintheOmni3DRayModel.

Aftercalculation,theusermayselectasubsetoftracesbasedon:

∙Theoffsetofeachtrace,whichisthehorizontaldistancebetweentheShotandtheReceiver.

∙Theazimuthofeachtrace,whichisthedirectionfromtheShottotheReceiver.

∙TheNMOstretchofeachtrace,whichisthepercentagebywhichthetraceisstretchedintimerelativetoazero-offsettrace.

SyntheticAnalysis

Calculatesanddisplayssynthetictracesusingray-tracing.TheresultingdataarestoredinSEGYdiskfileformatandmaybeloadedintoexternalsoftwareforprocessing.

ThisanalysisuseseitheranOmniTargetModel,orOmni3DRayModelasinput,todescribethegeology.

Tracesarecalculatedusingoneof2ray-tracingoptions:

1.SimpleMigratedray-tracingonanOmniTargetModelhorizon.Onlyonehorizonmayberay-tracedusingthismethod.Withinthisoption,2ray-tracingmethodsarepossible:

▪Curvedray.InthiscaseboththeShotandReceiverareassumedtobeatzeroelevation,buttheraypathsarecurvedbasedonthevelocitymodelasdescribedintheOmniTargetModel.

▪StraightRay.InthiscasetheShotandReceiverelevationsattributesareused,buttheraypathsarestraight.I.e.thevelocitymodelintheOmniTargetModelisignoredandaconstantvelocityisassumed.ThismethodisnotsuitableforVSPsurveys.

2.Complexray-tracingonanOmni3DRayModel.Thisisfull3DcurvedraytracingofallhorizonsdescribedwithintheOmni3DRayModel.BothShotandReceiverelevationsareused,andraysarecurvedthroughthevelocitymodeldescribedwithintheOmni3DRayModel.

Optionally,asubsetoftracesmaybeselectedatcalculationtime,byspecifyingarangeofacceptabletraceoffsetsand/orazimuths.

StackAnalysis

Calculatesanddisplaysastackvolumeoftracedata.InputtracesarestackedusinginformationfromtheSurveyScriptorStreamergeometry.

TheinputtracestobestackedaresuppliedfromaSEGYFiledefinedbyoneof4methods:

1.AsyntheticshotgathercreatedfromanOmnivelocityfunction.Thevelocityfunctionisaseriesof（velocity,time,Q）triples.Areflectioneventiscalculatedateachinflectionpoint.Arangeoftraceoffsetsarecalculatedandlinearnoisemaybeaddedtotheshotgather.NMOisthenappliedtothetracestopreparethemforstacking.

2.Afull3DsyntheticsurveygeneratedfromanOmniTargetModel.SeetheSyntheticAnalysisfordetailsofhowtheinputiscalculated.NMOisthenappliedtotheresulting3DSynthetic,whichisthenstackedtoproducea3Dstackvolume.

3.Auser-suppliedSEGYshotorCDPgatherrepresentativeoflocaldata,forexamplefromaprevious2Dseismicline.ThegathershouldalreadyhaveNMOappliedandbereadyforstacking.Inthiscase,thesinglegatherisusedasinputstackingtracesforalloutputbins.

4.Auser-supplied2DlineofSEGYshotorCDPgathersrepresentativeoflocaldata.ThedatashouldalreadyhaveNMOappliedandbereadyforstacking.Inthiscase,foreachoutputbintheclosestinputgatherisusedforstacking.

InputtracesfromtheSEGYFilearethenstackedateachbin-gridcellusingthefollowingalgorithm:

∙Allofthetracepairs（fromtheSurveyScriptorStreamer）arebinnedattheShot-Receivermidpoint.

∙Then,withineachbin:

oAllofthetraceoffsets（Shot-Receiverdistances）aresaved.

oForeachoffset,atraceisselectedfromtheSEGYFilethathasanoffsetclosesttothecalculatedoffset,andisthenstackedinthebincell.

TheresultingoutputisaSEGYstackvolumeoftracedata.

Optionally,asubsetoftracesmaybeselectedatcalculationtime,byspecifyingarangeofacceptabletraceoffsetsand/orazimuths.

PSTMImpulseAnalysis

CalculatesanddisplaystheeffectofapplyingPre-StackTimeMigration,foradatasetacquiredusingaspecificgeometry.

Thereare2calculationmethodsavailable:

1.Thismethodsimulatesasyntheticdatasetacquiredoveraplanardippingreflector,andthenappliesPSTM,usingthefollowingalgorithm:

oForeachinputShot-Receivertracepair,areflectiontimefromthedippingreflectoriscalculated.

oAsynthetictraceiscreatedbycreatingaRickerwaveletatthereflectiontime.

oThen,foreachoutputBinGridcellanoutputtraceisconstructed.

oForeachtimesampleontheoutputtrace"t-output",foreachnearbyinputtrace:

▪Locatethesamplevalueontheinputtracewhichisthesametime-distancefromtheinputShotandReceiver,ast-output.

▪Addtheinputsamplevaluetotheoutputsample.Optionally,thesamplevaluesmaybescaledand/ornormalized.

oTheresultingoutputtraceisthentimeshiftedbythereflectortimetoremovethetimeeffectofthedippingreflector.ThisallowsforeasiercomparisonoftheeffectofPSTMontheimpulsewavelet.

2.Thismethodsimulatesasyntheticdatasetacquiredfromaseriesofoneormoresubsurfacediffractingpoints,andthenappliesPSTM,usingthefollowingalgorithm:

oForeachinputShot-Receivertracepair,atimefromeachdiffractionpointiscalculated.

oAsynthetictraceiscreatedbyaddingaspikeateachdiffractiontime.

oThen,foreachoutputBinGridcellanoutputtraceisconstructed.

oForeachtimesampleontheoutputtrace"t-output",foreachnearbyinputtrace:

▪Locatethesamplevalueontheinputtracewhichisthesametime-distancefromtheinputShotandReceiver,ast-output.

▪Addtheinputsamplevaluetotheoutputsample.Optionally,thesamplevaluesmaybescaledand/ornormalized.

oTheresultingoutputtraceisthentimeshiftedbythereflectortimetoremovethetimeeffectofthedippingreflector.ThisallowsforeasiercomparisonoftheeffectofPSTMontheinputdiffractions.

Optionally,asubsetoftracesmaybeselectedatcalculationtime,byspecifyingarangeofacceptabletraceoffsetsand/orazimuths.

PSTMVolumeAnalysis

ThisanalysiscalculatesanddisplaystheresultofapplyingPre-Stack-Time-Migration.InputtracesaremigratedusinginformationfromtheSurveyScriptorStreamergeometry.

TheinputtracestobemigratedaresuppliedfromaSEGYFiledefinedbyoneof2methods:

1.As