基于入射角的AVO近似彈性波阻抗方程及反演Introduction

Amplitude-versus-offset(AVO)analysisiswidelyusedintheseismicexplorationindustryasameanstoestimatethereservoirpropertiesofsubsurfaceformations.AVOanalysishasproventobeeffectiveindetectingandcharacterizinggasandoil-bearingreservoirsbasedonchangesintheamplitudeofthereflectedseismicsignalasitisaffectedbyvariationsinthesubsurfaceproperties.Inthispaper,wepresentaderivationoftheAVOapproximationelasticwaveimpedanceequationbasedontheincidentangle,followedbyadiscussiononhowtousethisequationforinversiontoestimatereservoirparameters.

Methodology

TheAVOapproximationelasticwaveimpedanceequationbasedontheincidentangle,alsoknownastheZoeppritzequations,arederivedbasedontheconservationofenergyandthecontinuityofstressanddisplacementattheinterfacebetweentwomedia.Theequationisgivenas:

\begin{equation}

\frac{\DeltaV_{p}}{V_{p}}=A+B\text{sin}^2(\theta_i)+C\text{sin}^2(\theta_i)\text{tan}^2(\theta_i)

\end{equation}

where$\DeltaV_{p}/V_{p}$istheseismicreflectioncoefficient,$\theta_i$istheincidentangle,andA,B,andCarecoefficientsthatdependontheelasticpropertiesofthetwomedia.

Inordertoestimatethereservoirparameters,theAVOequationisinvertedusingvariousmethods.Oneofthemostcommonmethodsistofittheinversionmodeltotheobservedseismicdatabyminimizingthedifferencebetweenthepredictedandobservedreflectioncoefficients.Thisistypicallydoneusingleast-squaresoptimizationtechniques.Alimitationofthismethodisthatitmayleadtonon-uniquesolutions,wheremultiplesetsofparameterscanprovideagoodfittotheseismicdata.

AnothermethodisBayesianinversion,whichaccountsfortheuncertaintyinthemeasureddataandprovidesaposteriordistributionofthereservoirparameters.Thismethodhasbeenincreasinglyusedinrecentyearsduetoitsabilitytoprovideprobabilisticestimatesofreservoirpropertiesandtoquantifytheuncertaintyassociatedwiththeestimates.

Results

TheAVOapproximationelasticwaveimpedanceequationbasedontheincidentangleprovidesapowerfultoolforestimatingthereservoirpropertiesofsubsurfaceformations.Theequationhasbeenusedsuccessfullyinavarietyofenvironments,includingsandstone,shale,andcarbonatereservoirs.InversionoftheAVOequationusingavarietyofmethodshasledtovaluableinsightsintothesubsurfaceproperties,suchasporosityandfluidcontent,andhashelpedtoguideexplorationandproductionactivities.

Conclusion

AVOanalysishasbecomeanintegralpartoftheseismicexplorationindustryduetoitsproveneffectivenessindetectingandcharacterizinghydrocarbonreservoirs.TheAVOapproximationelasticwaveimpedanceequationbasedontheincidentangleprovidesapowerfultoolforestimatingthereservoirpropertiesofsubsurfaceformations,andinversionofthisequationusingavarietyofmethodshasledtovaluableinsightsintothesubsurfaceproperties.Whilethetechniquespresentedinthispaperhavebeensuccessful,furtherresearchisneededtoimprovetheaccuracyandresolutionofinversionmethodsandtocontinuetoadvancethestate-of-the-artinthefieldofseismicexploration.Inadditiontothemethodsdiscussedabove,thereareanumberofothertechniquesusedinAVOanalysistoestimatereservoirproperties.OnecommonlyusedapproachistoanalyzetheAVOresponseintermsoftheinterceptandgradientofthereflectioncoefficient,whichcanprovideinformationonthefluidcontentandporosityofthereservoir.AnotherapproachinvolvesmodelingtheAVOresponseusingforwardmodelingtechniques,whichcanhelptoidentifythekeyparametersthatcontroltheAVOresponseandcanbeusedtoconstraintheinversion.

AVOanalysishasalsobeencoupledwithothergeophysicaltechniques,suchasseismicamplitudeinversionandelasticinversion,toimprovetheaccuracyandresolutionofreservoirparameterestimation.Thesetechniquesuseadditionalinformationfromtheseismicdata,suchasamplitudevariationwithfrequencyortimedelays,tofurtherconstraintheinversionandimprovethediscriminationbetweendifferentreservoirproperties.

DespitethesuccessofAVOanalysis,therearestillsignificantchallengesassociatedwithaccuratelyestimatingreservoirpropertiesfromseismicdata.Theeffectsoflateralvariationsinlithologyandfluidcontent,aswellasthepresenceofanisotropyinthesubsurface,cancomplicatetheAVOresponseandleadtouncertaintiesintheinversionresults.Additionally,thelimitationsinseismicdataacquisitionandprocessingcanlimittheresolutionandaccuracyoftheinversion.

Inconclusion,AVOanalysisisapowerfultoolforestimatingreservoirpropertiesfromseismicdata,butitrequirescarefulinterpretationandmodelingtoaccuratelyestimatethesubsurfaceproperties.OngoingresearchanddevelopmentisneededtoimprovetheaccuracyandresolutionofAVOtechniquesinordertosupportincreasedexplorationandproductionefforts.OneareaofongoingresearchinAVOanalysisisthedevelopmentofadvancedmodelingtechniquesthatcanaccountforthecomplexsubsurfacegeologyandimprovetheaccuracyoftheinversion.Thisincludestheuseoffullwaveforminversion(FWI),whichusesamoredetailedrepresentationoftheseismicwavefieldandcanprovideamoreaccurateestimateofthesubsurfaceproperties.FWIcanalsoaccountfortheeffectsofanisotropy,whichcanplayasignificantroleintheAVOresponse.

AnotherareaofresearchistheintegrationofAVOanalysiswithothergeophysicalandgeologicaldata,suchaswelllogs,rockphysicsmodels,andreservoirsimulations.Bycombiningthesedifferentsourcesofinformation,itispossibletobuildmoreaccuratemodelsofthesubsurfaceandachieveamorerobustestimateofreservoirproperties.

Inaddition,machinelearningandartificialintelligencetechniquesarebeingappliedtoAVOanalysistoimprovetheinterpretationandspeeduptheinversionprocess.Thesemethodsusealgorithmstoidentifypatternsintheseismicdataandpredictthesubsurfaceproperties,whichcanhelptoovercomesomeofthelimitationsoftraditionalAVOanalysisandimprovetheefficiencyoftheinterpretationprocess.

Ultimately,thesuccessofAVOanalysisinestimatingreservoirpropertiesdependsonthequalityoftheseismicdata,theaccuracyofthemodeling,andthedepthofunderstandingofthegeologyandfluiddynamicsofthesubsurface.Asthesetechnologiesandtechniquescontinuetoevolve,AVOanalysiswillcontinuetobeacriticaltoolforreservoircharacterizationandoptimizationintheoilandgasindustry.AnotherareaofongoingresearchinAVOanalysisisthedevelopmentofmethodstoaccountforthepresenceofgasinthesubsurface.GasreservoirscanhaveasignificantimpactontheAVOresponse,leadingtosignificantvariationsintheseismicamplitudewithoffsetandangle.Thiscancomplicatetheinversionprocessandmakeitdifficulttoaccuratelyestimatereservoirproperties.ResearchersaredevelopingmethodstoaccountforgaseffectsinAVOanalysis,usingtechniquessuchasAVOmodelingwithagasindicator,jointinversionofseismicandwelldata,androckphysicsmodelsthatincorporatetheeffectsofgassaturationandpressure.

AnotherareaofinterestistheapplicationofAVOanalysisinunconventionalreservoirs,suchasshalegasandoilformations.Inthesereservoirs,theAVOresponsecanbecomplexandhighlyvariable,makingitchallengingtoaccuratelyestimatereservoirproperties.ResearchersaredevelopingnewmethodstoanalyzetheAVOresponseinunconventionalreservoirs,suchaspre-stackinversionandelasticseismicinversion,whichcanprovideamoredetailedunderstandingofthereservoirproperties.

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