弹性波阻抗理论和实现方法

弹性阻抗理论,利用Hampson-Russell软件实现弹性波阻抗反演,2020/5/13,.,介绍,先回顾弹性阻抗反演的原理,然后利用Hampson-Russell一组软件分析弹性阻抗反演一个实际例子.弹性阻抗ElasticImpedance(EI)是由BP公司PatrickConnolly提出.实现弹性阻抗反演可用AVO和STRATA软件自然组合来完成.在谈论弹性阻抗反演之前,简单回顾反演方法在地震勘探运用的历史.,2020/5/13,.,CDP/CRP道集,迭加,反演,估算Z=VP,地震岩性估算,传统的地震岩性估算是在地震数据叠加偏移后数据(叠后数据)道进行反演.这只能估算声阻抗,不足于推测流体成分.,2020/5/13,.,道集,叠加,反演,AVO分析,属性1,属性2,估算VP,VS,和,估算Z=VP,AVO方法同时使用多属性估算VP,VS,和,可估算推测流体和岩性.,2020/5/13,.,AVO分析可能用的属性,但是哪两种(或更多属性)可用来最好地预测流体和岩性这些参数?目前AVO可提取和使用的一系列不同属性:偏移距或角度段限(范围限制)叠加弹性阻抗反演截距和梯度提取的纵横波反射系数RP,RS由RP和RS反演到纵横波阻抗ZP,ZS纵横波阻抗ZP,ZS转换Lambda-Mu-Rho分析本讨论先使用前面两个属性的方法.后面再讨论其它的属性方法.,2020/5/13,.,范围限制叠加,道集,AVO分析,近叠加,远叠加,以上是范围限制叠加的简单流程.利用常偏移距或常角度的范围叠加已经非常成熟.问题是如何解释其结果?,2020/5/13,.,(a),(b),近角度(0o-15o)叠加远角度(15o-30o)叠加数据来自加拿大Colony区块.在630MS有一个“亮点”震幅在远角度叠加上比近角度叠加要强的多.从井资料分析这是气砂岩导致“亮点”.,气砂岩范围限制叠加,2020/5/13,.,这是近远偏移距(角度)的交绘图,高震幅区块用不同颜色突出显示.,角度叠加进行交绘图,2020/5/13,.,这是交绘图中的突出区块对应在剖面上的位置.可看出气砂岩已被很好地描绘.,2020/5/13,.,(a)近角度叠加(0-15o)时间切片,(b)远角度叠加(15-30o)时间切片(三维河道砂).对时间切片震幅包络求得是10MS窗口内的平均值并运用了Z-SCORE转换.异常河道砂得以清楚显示.,角度范围叠加,(a),(b),2020/5/13,.,从范围限制叠加到弹性阻抗,范围限制叠加使用的是常偏移距或常相位道集,方法很成熟并可避免同相轴未拉平问题.但它究竟有何含义?PatrickConnolly(BP),提出新颖的方法来解释范围叠加的含义,称之为弹性阻抗.弹性阻抗是基于Aki-Richards等式,下几张图片解释弹性阻抗的概念和由来.,2020/5/13,.,弹性阻抗理论,Aki-Richards等式可写为(三项式):,Connolly(1999)提出,类似于声阻抗,我们定义弹性阻抗(EI)为:,2020/5/13,.,假设,注意到,我们可以把Aki-Richards等式重写为:,假设K为常数,可以将上式写为:,2020/5/13,.,然后进行积分和取幂,可得到以下弹性阻抗EI等式:,如果=0o,EI弹性阻抗就还原为声阻抗(AI),等式为:,2020/5/13,.,以上等式使用的是Aki-Richards所有三项等式.对于入射角大于300,该等式将不是线性的拟合.对于大角度(大偏移距),如果只用等式的前两项,等式可写为:,当=0o,得到:,2020/5/13,.,将声阻抗(AI)转换入射角为30的弹性阻抗通常曲线类似但阻抗绝对值变低.角度增加其视声波阻抗降低.油砂岩比页岩视声波阻抗降低幅度更大.如下图,Connolly1999,弹性阻抗油饱和度的影响,2020/5/13,.,弹性阻抗实例,下图显示声阻抗和弹性阻抗(30度角)的曲线比较:,2020/5/13,.,重叠显示更好地区分弹性阻抗和声阻抗在含油砂岩处的差别:,2020/5/13,.,EI反演步骤,道集,AVO分析,近角度叠加q1,远角度叠加q2,反演弹性阻抗EI(q1),反演弹性阻抗EI(q2),2020/5/13,.,CaseStudyfromtheColonySandPlayinAlberta,Canada,2020/5/13,.,ApplyingElasticImpedancetotheColonyData,Inthisexercise,wewillstartwiththe2DColonydatasetwhichweanalyzedearlierandapplytheElasticImpedanceanalysistoit.,Firstre-opentheavo_classdatabaseinGEOVIEW.OntheGEOVIEWwindow,clickonDatabase/Open.Selectavo_class.wdbfromthepullDownlist,asshown,andclickonOK:,2020/5/13,.,OntheGEOVIEWmainwindow,clickontheAVO/AVObuttontorestarttheAVOprogram:,SelecttheoptiontoOpenPreviousProjectandchoosethecolony.prjproject:,2020/5/13,.,Beforeanalyzingthedata,wewillcreatetheelasticimpedancelogsinthemodelingwindow.Ifitisnotvisible,clickontheModeling/SingleWellbuttononaseismicwindowandselectAVO_WELLontheOpenWellmenutogetthefollowingwindow:,2020/5/13,.,Next,clickontheLogs/Transformsbuttonasshownontheleft,andselecttheElasticImpedanceoptionfromtheTransformsmenushownbelow:,2020/5/13,.,ClickNextontheTransformsmenuandselectthecorrectwell(AVO_WELL)fortheP-andS-wavelogsandforstoringtheElasticImpedancelog,asshownbelow.,2020/5/13,.,Onthenextmenu,makesuretheFRMeditedlogsareusedforthecalculationoftheelasticimpedanceandcalltheresultEI_Nearasshown.,2020/5/13,.,ClickonNextandfillinthenextmenuasshown,choosingConstantAngleandfillinginanangleof7.5degrees.,2020/5/13,.,WhentheEI_Nearloghasbeencreated,selecttheLogs/Transformsoptionagain,andfillinthemenusasshownpreviouslyexceptforthelasttwomenusshownhere.Onthesemenus,createanewlogcalledEI_Far(makingsurethattheFRMeditedlogsareusedinthecalculation)ataconstantangleof22.5degrees.,2020/5/13,.,Todisplaythetwoelasticimpedancetracestogether,clickonthe“eyeball”icontobringuptheParametermenu.UndertheLayouttab,turnofftheDisplayOnlyActiveLogsbuttontoseeallofthelogs,andputtheEI_NearandtheEI_Farlogsonthesametrack,asshown.,2020/5/13,.,ClickonOkandyouwillseethedisplaybelow.NoticethattheEI_Farlogplotstotheleftinthegaszoneandtotherightintherestofthelog.Now,letscrossplotthesetwologs.,2020/5/13,.,ClickonCrossplotandfilloutthemenuasshownbelow,selectingtheElasticImpedancelogtypeaswellasand.,Then,clickonNext.,Onthismenu,selectthewell,andclickonNext.,2020/5/13,.,Onthismenu,selectElasticImpedanceforboththeXandYaxes,andchangethePlotTitleasshownbelow.(Notethatwewillselectadifferentelasticimpedancelogforeachaxisonthenextmenu).ClickonNext.,2020/5/13,.,Onthismenu,selectEI_NearfortheXaxisandEI_FarfortheYaxis,asshown.ClickonNext.,Onthismenu,selectTimeasthedomain,withstartandendvaluesof600and675.ClickonOktogetthecrossplot.,2020/5/13,.,Noticethattheaxesoftheplotarebothlabeledthesame.Tochangetheannotation,clickonEdit/Annotationsandchangethemenuasshownontheright:,ClickonOkandtheplotwillappearasshownontheleft.Noticetheclearseparationofthepointsonthelowerleftoftheplot.,2020/5/13,.,Letusnowperformzoneanalysistoseeiftheanomalyseenonthecrossplotreallyisthegassand.Todothis,firstdisplaythewelllogcurvesbyclickingontheCross-Sectionbutton.AfterusingtheZoomoption,youshouldseeaplotsimilartothis:,2020/5/13,.,Now,clickontheZones/Addoptionandcreatetheellipticalgreybackgroundtrendasshownontheright.,2020/5/13,.,Nowdefinetheellipticalyellowgastrendasshown.,2020/5/13,.,Notethattheplotofthewelllogshasbeenupdatedwiththecolors,andtheanomalouspointsdoindeedcorrespondtothegassandzone.,2020/5/13,.,NowgotothewindowcontainingtheoriginalCDPgathers.ClickonProcess/Stack/RangeLimitedStack:,2020/5/13,.,Usethedefaultsonthefirstmenuasshownontheright,andclickonNext.,Then,fillinthesecondmenuasshownontheleft.Noticethatwearecreating2anglestacksfrom0to30degrees.,2020/5/13,.,Thetwoanglestacksarecreatedasshownhere,whererange_limit_stackisthenearanglestack,andrange_limit_stack2isthefaranglestack.,2020/5/13,.,Selectthefilecalledrange_limit_stack.volfromthemenuandclickonOpen.,Next,clickontheSTRATAbuttonontheGEOVIEWmainwindow.Wewillcontinueusingthecolonyproject,asindicatedinthemenuontheright.,ClickonOktobringuptheSTRATAmainwindow,andthenclickonDataManager/ImportData/OpenSeismic/OpenFromProject.,2020/5/13,.,FillouttheWelltoSeismicMapmenuasshownandclickOk.,TheSTRATAwindownowlookslikethis:,2020/5/13,.,ClickonHorizon/PickHorizonsandpickasecondevent,asshown.Horizon1isthetroughatthetopofthegassand.,2020/5/13,.,Finally,pickathirdevent,asshownhere.ThenclickOktofinishthepicking.,2020/5/13,.,Next,clickonModel/Build/RebuildaModel.Fillinthefirstpageasshownontheright,changingtheoptionto:TypicalsetupofElasticImpedanceforfar-offsetstackinversion.ClickonNext.,Onthethirdpage,selectthewellAVO_WELLandclickNext.,2020/5/13,.,Onthenextpage,wemustselecttheElasticImpedancelogwhichcorrespondstotheNearAnglestack.Sincethisstackcoversananglerangeof0to15degrees,chooseEI_Near,calculatedfortheangleof7.5degrees.,NowclickonNexttwiceandOKtobuildthemodel.,Then,clickonInvert/ModelBasedasshown:,Onthefirstpage,changetheoutputfilenametonear_inversion.ClickonNexttwice.,Onthethirdpage,changetheAverageBlockSizeto4.ClickOKtoruntheinversion.,2020/5/13,.,Theinversionresultwilllooklikethis:,2020/5/13,.,Next,clickonWindow/NewWindowtocreateanemptySTRATAwindow.Inthisnewwindow,clickonDataManager/ImportData/OpenSeismic/OpenFromProjectandselectrange_limit_stack2.vol,asshownontheright.ClickonOpentogettheresultshownbelow.Noticethattheexistingpicksareannotated.,2020/5/13,.,Next,clickonModel/Build/RebuildaModelandselecttheoptionTypicalsetupofElasticImpedanceforfar-offsetstackinversiononthefirstpage,asdonepreviously.SelectAVO_WELLonthethirdpageandchoosetheEI_Farlog(22.5degrees)onthefourth,asshown.Thenewmodelwilllooklikethis(youmayneedtoupdatethecolorkey):,2020/5/13,.,Next,clickonInvert/ModelBasedandchangethenameoftheoutputvolumeontheinversionmenuasshownbelow.,Onthethirdpage,changetheAverageBlockSizeto4andclickonOKtostarttheinversionprocess:,2020/5/13,.,Wenowhavetwoinversionresults.Notethatwehavehadtousetwodifferentcolorscales,sincetheimpedancevaluesarescaleddifferently.,Near_inversion,Far_inversion,2020/5/13,.,Nowletuscomparethenear-angleinversionwiththefar-angleinversionbycross-plottingthetwovolumes.,Oneitherofthetwoinversionresults,clickonProcess/CrossPlot:,Onthefirstmenupage,selecttheCDPrangefrom300to360andthetwovolumesasshown:,ClickNextuntilyoureachthefourthpage.SpecifyaConstantTimeof630msasshown:,2020/5/13,.,IftherewerenoAVOeffects,wewouldexpectthefarandnearimpedancestoberelatedbyastraightline.Inotherwords,therewouldbeasinglecluster.Letsaddsomezonestothecrossplotandviewthecross-sectiontoseewherethesezoneslie.ClickonZones/Add:,2020/5/13,.,Makethefirstzoneusinganellipseandplaceitalongthemainaxis,asshown.PresstheApplybuttontosaveth