可控震源記錄中的脈沖噪聲分析

可控震源記錄中的脈沖噪聲分析Abstract

Pulsenoiseisamajorsourceofinterferenceforcontrolled-sourceseismicrecords.Inthispaper,weanalyzethepulsenoisepresentinasetofcontrolled-sourcerecordsacquiredintheGulfofMexico.Weuseawavelettransformbasedapproachtoidentifyandquantifythepulsenoiseintherecords.Wealsoinvestigatetheeffectsofpulsenoiseonthequalityoftherecordsanddiscussthestrategiesthatcanbeemployedtomitigateitseffects.

Introduction

Controlled-sourceseismicsurveysareusedforavarietyofapplicationsintheoilandgasindustry,includingexploration,reservoircharacterization,andproductionmonitoring.Thesesurveysinvolvegeneratingacousticsignalsusingcontrolledsourcesandrecordingthereflectedwavesusingreceiversdeployedonthesurfaceorontheseabed.Oneofthemajorchallengesincontrolled-sourceseismicsurveysisthepresenceofvarioustypesofnoisethatcaninterferewiththerecordedsignals.

Pulsenoiseisacommonformofnoisethatispresentincontrolled-sourcerecords.Thisnoiseischaracterizedbyshort-duration,high-amplitudespikesthatcanbeseeninthetimedomain.Pulsenoiseisoftenattributedtoelectromagneticinterference(EMI)causedbytheoperationofnearbyequipment,suchaswinches,engines,orpowersupplies.

Inthispaper,weanalyzethepulsenoisepresentinasetofcontrolled-sourcerecordsacquiredintheGulfofMexico.Weuseawavelettransformbasedapproachtoidentifyandquantifythepulsenoiseintherecords.Wealsoinvestigatetheeffectsofpulsenoiseonthequalityoftherecordsanddiscussthestrategiesthatcanbeemployedtomitigateitseffects.

Methodology

Weusedasetofcontrolled-sourcerecordsacquiredintheGulfofMexicotostudytheeffectsofpulsenoiseonthequalityoftherecords.Therecordswereacquiredusingamarineseismicacquisitionsystemthatconsistedofasourcevesselandanarrayofreceiversdeployedontheseabed.Thesourcevesselgeneratedacousticsignalsusingairgunsandthereceiversrecordedthereflectedwavesusinghydrophones.

Toanalyzethepulsenoiseintherecords,weusedawavelettransformbasedapproach.Thewavelettransformisamathematicaltoolthatdecomposesasignalintoseveralfrequencycomponents.Itcanbeusedtoanalyzesignalswithnon-stationarycharacteristics,suchastheseismicrecordsacquiredinthisstudy.

Weappliedthewavelettransformtotherecordsandidentifiedthefrequencycomponentsthatcorrespondedtothepulsenoise.Wethenquantifiedtheamplitudeanddurationofthepulsesusingathreshold-basedapproach.Wedefinedathresholdbasedonthenoiselevelintherecordsandclassifiedanypulsethatexceededthisthresholdasapulsenoise.

Results

Theanalysisofthepulsenoiseinthecontrolled-sourcerecordsrevealedthatthenoisewaspresentinalloftherecords.Theamplitudeanddurationofthepulsesvariedbetweentherecords,withsomerecordsexhibitingmoreseverepulsenoisethanothers.

Thepulsenoisehadasignificanteffectonthequalityoftherecords,especiallyatlowfrequencies.Thenoisereducedthesignal-to-noiseratio(SNR)andmadeitdifficulttointerprettheseismicimages.Thenoisealsointroduceddistortionsinthewaveforms,whichmadeitdifficulttoidentifyandlocatesubsurfacestructures.

Discussion

Thepresenceofpulsenoiseincontrolled-sourcerecordsisacommonproblemthatcanhaveasignificantimpactonthequalityoftherecords.ThenoiseisoftenattributedtoEMIcausedbytheoperationofnearbyequipmentorthepresenceofothersourcesofelectricalnoise.

Tomitigatetheeffectsofpulsenoise,itisimportanttouseappropriatefilteringtechniquesthatcanremovethenoisewithoutdistortingthesignals.Oneapproachthathasbeenusedsuccessfullyistheuseofwaveletdenoisingtechniquesthatexploitthefrequency-timelocalizationpropertiesofthewavelettransform.Thisapproachcaneffectivelyremovethepulsenoisewhilepreservingtheimportantfeaturesofthesignals.

Conclusion

Inthispaper,weanalyzedthepulsenoisepresentinasetofcontrolled-sourcerecordsacquiredintheGulfofMexico.Weusedawavelettransformbasedapproachtoidentifyandquantifythepulsenoiseintherecords,andinvestigateditseffectsonthequalityoftherecords.Wealsodiscussedthestrategiesthatcanbeusedtomitigatetheeffectsofpulsenoise.Ourresultsshowedthatpulsenoisecanhaveasignificantimpactonthequalityofcontrolled-sourcerecordsandthatappropriatefilteringtechniquescanbeusedtomitigateitseffects.Inadditiontowaveletdenoisingtechniques,thereareotherstrategiesthatcanbeemployedtomitigatetheeffectsofpulsenoise.OneapproachistouseshieldingtoreducetheEMIcausedbynearbyequipment.Thiscanbeachievedbyenclosingtheequipmentinametalshieldorbyplacingtheequipmentfartherawayfromtheseismicreceivers.

Anotherapproachistousetime-domainfilteringtechniques,suchasnotchfiltersormedianfilters.Thesetechniquescanremovethepulsenoisebysuppressingthehigh-amplitudespikeswhilepreservingtheunderlyingsignals.However,thesefiltersmayalsoaffecttheshapeandamplitudeofthesignals,andtherefore,shouldbeappliedwithcaution.

Itisalsoimportanttoensurethattherecordingequipmentisproperlygroundedandthatelectricalinterferenceisminimized.Propergroundingisessentialtoreducetheimpactofgroundloopsandtoensurethattherecordedsignalsarenotsubjecttoelectricalnoise.

Inconclusion,pulsenoiseisacommonproblemincontrolled-sourceseismicsurveysthatcanhaveasignificantimpactonthequalityoftherecordeddata.Itisimportanttouseappropriatefilteringtechniques,suchaswaveletdenoisingortime-domainfiltering,tomitigatetheeffectsofpulsenoisewhilepreservingtheimportantfeaturesofthesignals.PropergroundingandshieldingcanalsohelpreducetheimpactofpulsenoiseandothertypesofEMI.Anotherstrategyformitigatingtheeffectsofpulsenoiseistouseavariable-lengthwindowingapproach.Thismethodinvolvesdividingtheseismicsignalintooverlappingwindows,wherethewindowlengthvariesaccordingtothesignal'slocalnoiselevel.Inareaswithhighnoiselevels,shorterwindowscanbeusedtomitigatetheeffectsofpulsenoise,whilelongerwindowscanbeusedinareaswithlownoiselevelstopreservesignaldetail.

Machinelearningapproaches,suchasdeeplearningandartificialneuralnetworks,canalsobeutilizedtosuppresspulsenoiseinseismicdata.Thesetechniquescanlearntoidentifyandremovepulsenoisebytrainingonlargedatasetsofseismicdatawithknownnoiselevels.

Itisimportanttonotethatwhilethesetechniquescanbehighlyeffectiveinsuppressingpulsenoise,theymayalsointroduceotherartifactsordistortionsintothedata.Therefore,carefultestingandvalidationofanynoisesuppressionmethodsarenecessarytoensurethattheydonotadverselyaffecttheaccuracyorprecisionofseismicdata.

Insummary,severalstrategiescanbeemployedtomitigatetheeffectsofpulsenoiseincontrolled-sourceseismicsurveys,includingwaveletdenoising,time-domainfiltering,variable-lengthwindowing,machinelearning,andpropergroundingandshielding.Theselectionofthemostappropriatetechniquewilldependonfactorssuchasthenoiselevel,signalcharacteristics,anddesiredsignal-to-noiseratio.Byusingthesetechniqueseffectively,researcherscanobtainhigher-qualityseismicdata,improvingtheaccuracyandreliabilityofinterpretationsandpredictionsbasedonthatdata.Anothereffectiveapproachformitigatingtheeffectsofpulsenoiseinseismicdataisfrequency-domainfiltering.Thistechniqueinvolvestransformingtheseismicsignalfromthetimedomaintothefrequencydomain,wherenoisecanbeidentifiedandremovedviafiltering.

Acommonfrequency-domainfilterforsuppressingpulsenoiseisthef-xdeconvolutionfilter.Thisfilterattemptstoremovethenoisebydividingthesignalspectrumbyanestimateofthenoisespectrum,derivedfromanon-noise-contaminatedreferencetraceorfromthesignalitself.Thefiltercoefficientsarecomputedinthefrequencydomainandappliedtoindividualtracespectra.Thistechniquecanbehighlyeffectiveinattenuatingpulsenoise,butitcanalsoremovesomeofthesignalenergyinareaswherethesignalandnoiseoverlapspectrally.

Otherfrequency-domainfilters,suchastheWienerfilterandthespectralwhiteningfilter,canalsobeusedtosuppresspulsenoiseinseismicdata.Thesefiltersestimatethesignalandnoisespectraandapplyaweightingfunctiontothesignalinordertosuppressthenoise.Theefficacyofeachfilterwilldependonthecharacteristicsofthenoiseandsignal,aswellasthefilterparametersandthesignal-to-noiseratio.

Finally,itisw