岩石物理模拟软到硬结晶岩沉.docx
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岩石物理模拟软到硬结晶岩沉.docx
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岩石物理模拟软到硬结晶岩沉
Rockphysicsmodelingofsoftsedimentarytohardcrystallinerocksfor
rockengineeringapplications
ToruTakahashi
FukadaGeologicalInstitute,2-13-12Honkomagome,Bunkyo,Tokyo113-0021,Japan
SoichiTanaka
FukadaGeologicalInstitute,2-13-12Honkomagome,Bunkyo,Tokyo113-0021,Japan
Copyright2008,ARMA,AmericanRockMechanicsAssociation
ThispaperwaspreparedforpresentationatSanFrancisco2008,the42nd
USRockMechanicsSymposiumand2nd
U.S.-CanadaRockMechanicsSymposium,heldinSanFrancisco,June29-
July2,2008.
ThispaperwasselectedforpresentationbyanARMATechnicalProgramCommitteefollowingreviewofinformationcontainedinanabstractsubmittedearlierbytheauthor(s).Contentsofthe
paper,aspresented,havenotbeenreviewedbyARMAandaresubjecttocorrectionbytheauthor(s).Thematerial,aspresented,doesnotnecessarilyreflectanypositionofARMA,itsofficers,
ormembers.Electronicreproduction,distribution,orstorageofanypartofthispaperforcommercialpurposeswithoutthewrittenconsentofARMAisprohibited.Permissiontoreproduceinprint
isrestrictedtoanabstractofnotmorethan300words;illustrationsmaynotbecopied.Theabstractmustcontainconspicuousacknowledgementofwhereandbywhomthepaperwaspresented.
ABSTRACT:
Inrecentyears,rockphysicalinterpretationofseismicdatahasbeenaggressivelyusedinoilandgasindustryfor
characterizingandmonitoringoilandgasreservoirs.Inthisfield,onlysedimentaryrockssuchassandstonehavebeenmodeled
usingmainlyP-waveseismicdata.Inrockengineeringapplications,rockphysicalinterpretationofgeophysicaldatahasalso
becomemoreimportanttoobtainmechanicalandhydrogeologicalsubsurfacemodels.Inthoseapplications,notonlysedimentary
rocksbutalsovolcanicandcrystallinerocksmustbecharacterizedandmodeledforfurtheranalysis.Moregeophysicaldataother
thanP-waveseismicdataarepotentiallyavailableforrockphysicsmodelinginthisfield.Howevertherearenotsomanyrock
physicsmodelsforthosetypesofrockswithmanygeophysicaldata.Wehave,therefore,collectedgeophysicalpropertiesofthose
typesofrocksobtainedinlaboratorytestsandwellloggings.Thenwehavetriedtoapplytheexistingrockphysicsmodelstosoft
sedimentaryandcrystallinerockswhichareverycommonlycharacterizedinrockengineeringapplicationsinJapan.The
weatheredrockswerealsostudiedinmodeling.Thesetrialapplicationshaveclarifiedtheapplicabilityoftheexistingrockphysics
modelsandtheproblemstobeaddressedinthefuturestudyonrockphysicsmodelingofvarioustypesofrockstobecharacterized
inrockengineeringapplications.
1.INTRODUCTION
Inrecentyears,rockphysicalinterpretationofseismicdatahasbeenaggressivelyusedinoilandgasindustryforcharacterizingandmonitoringoilandgasreservoirsmainlyforsedimentaryrockssuchassandstonebecausemanyreservoirsarecomposedofsandstoneorshaly
sandstone.Inaddition,onlyseismicdatahavebeenusedtostudyrockphysicsmodelsbecausetheirresolution,qualityandreliabilityaresuperiortoothergeophysicaldataindeepoilandgasexploration.Inapplicationstorockengineering,rockphysicalinterpretationofgeophysicaldatahasbecomemoreimportanttoobtainquantitativemechanicaland
hydrogeologicalsubsurfacemodels.Inrockengineeringapplications,notonlysedimentaryrocks,butalsocrystallinerockssuchasgranitemustbecharacterizedandmodeledforfurtheranalysis.MoregeophysicaldataotherthanP-waveseismicdataarealsopotentiallyavailableforrockphysicsmodelinginthisfield.Howevertherearenotsomanyrockphysicsmodelsfor
thosetypesofrockswithmanygeophysicaldata.Wehavethereforestartedstudyingrockphysics
modelingofavarietyofrocksusingmanygeophysicaldataforrockengineeringapplications.WehavefirstcollectedgeophysicalandrockengineeringpropertiesofvarioustypesofrocksobtainedinlaboratorytestsandwellloggingsinJapan.ThenwehavetriedtoapplyexistingrockphysicsmodelstosoftsedimentaryandcrystallinerockswhichareverycommonlyencounteredinrockengineeringapplicationsinJapan,inordertoevaluatetheirapplicability.Inthispaperwedescribe
thesetrialapplicationsandtheirevaluationstoclarifytheproblemstobeaddressedinthefuturestudy.
2.ROCKPHYSICS
Rockphysicsisthesciencethataddressestherelationshipbetweenphysicalpropertiesofrocksandgeophysicaldata[2].Intherockphysics,arockis
modeledwithmicroscopicfeaturessuchasasandparticleanditsmacroscopicfeaturessuchaselasticandhydraulicpropertiesaredescribedbythepropertiesandinteractionofthosemicroscopicfeatures.Figure1showsthemicrographsoftherealrocksamplesandtheirrockmodelsrepresentedwithsand(largeopencircle)andclay(smallsolidcircle)particles[3].Calculatingmechanicalinteractionoftheseparticles,thetheoretical
relationshipbetweenelasticproperty,thecompressionalmodulusinthiscase,andporosityisderivedandcomparedtotherealdataobtainedfromwelllogsasshowninthisfigure.
RockphysicsmodelsproposedsofararesummarizedinFigure2.Inthisfigure,fivemodelsaredescribedbasedontherelationshipbetweenP-wavevelocityandporosity,whichisthemostimportantrelationforrockphysicsmodeling.Thesemodelsareproposedmainlyforgranularrockssuchassandstoneswithdifferentconsolidationsandclaycontents.Figure3showsan
exampleofapplicationofarockphysicsmodeltothemudstoneorshaleinthethreedifferentsites[3].Inthisexample,thefriablesandmodelorweaklycementedmodel(amodelforModelIIIintheFigure2)[1]isapplied.Compressionalandshearmoduli(dots)obtainedfromacousticanddensitylogsareplottedagainstporositycalculatedfromdensitylogs.Threetheoreticalcurves(solidlines)arecalculatedusingthemodelswiththreedifferentclaycontents,0,0.5and1.0.Itcanbeseenthatinspiteoftherocksatdifferentsitesanddepths,thesethreedatasetsaremodeledwellwithasinglerockphysicsmodel.
3.ROCKPHYSICSMODELINGEXAMPLES
Rockphysicshasnotbeensooftenappliedtotheinterpretationofshallowgeophysicaldatainrockengineering.Fortheapplicationsinthisfield,manytypesofrocksincludingvolcanicandcrystallinerocksaswellassedimentaryrocksmustbecharacterizedandmodeled.Howeverrockphysicsmodelsfortherocksbesidessandstoneswhicharethemajoroilandgas
reservoirrockshavenotbeenstudiedsomuch.Wehavethereforestartedcollectingthedataofgeophysicalandengineeringpropertiesofvarioustypesofrocksandstudyingtheirrockphysicsmodels.Thefollowingsaretwoexamplesofpreliminaryapplicationsofrockphysicsmodelstosoftmudstone/siltstoneandhardgranitewithcracks.Althoughtheseareonlytwotrialapplicationsatthismoment,theyclarifytheproblemstobeattackedinfuturestudyofrockphysics
modelingofthesetypesofrocks.3.1Applicationtosoftmudstone/siltstoneInthisapplicationP-andS-wavevelocitylogdataatfourdifferentsitesanddepthsareused.ThesevelocitylogswereacquiredinPliocene-Pleistocenemudstone/siltstoneforsitecharacterizationincivil
engineeringprojectsinJapan.Figure4showstheP-and
S-wavevelocityversusporositycross-plots.Itshouldbenotedthattheserockshaveveryhighporosityof50-60%.ReferringtotheexistingmodelsshowninFigure2,thefriablesandmodelortheweaklycementedmodelisalsoappliedtothesedata.TheoreticalP-wavevelocity-
porositycurves(solidlines)calculatedusingthismodelareshowninFigure5.Keyparametersusedinthis
calculationarepresentedinthefigure.Threecurvescorrespondtothosewiththreedifferentclaycontents,0,0.5and1.0.Thesecurvesfittherealdataverywell,clearlyshowingthattheexistingfriablesandmodelcanbeapplicabletosoftsedimentaryrockswithveryhigh
porosity,whichareoftenencounteredinrockengineeringapplicationsinJapan.
Figure6showstherigidity(S-wavemodulus)toporosityrelationforthesamerocksastheP-wavecase.Theoreticalcurves(solidlines)calculatedusingthefriablesandmodelwiththesameparametersasthoseforP-wavecaseareoverlaidontherealdata(dots).Itcan
threetypesofrocksexceptforsandstone,whichhaslowerporosityof30-40%thanthose(50-60%)forothers.Togetbetteragreement,thecoordinationnumber,oneof
keyparametersinagranularmodel,ischangedfrom5to9,becausethisnumberisstronglyrelatedtoporosity.Updatedtheoreticalcurveswithhighercoordination
numbershowninFigure7indicatebetteragreementtoallfourdatasets.
ThisapplicationrevelsthatS-wavepropertiesaremoresensitivetothemodelparametersthanP-waveones,meaningthatS-wavepropertytogetherwithP-waveone
shouldbeusedtomakeamoreaccuraterockphysicsmodel.
3.2ApplicationtograniteInthisapplicationP-wave(sonic)logdataacquiredincrackedgraniteareusedfortestingapplicabilityoftheexistingrockphysicsmodel.TheP-wavevelocity–porositycross-plotisshowninFigure8,wheretheporosityiscalculatedfromthedensitylogacquiredatthesametime.ThisgraniteismodeledbytheKuster-Toksozmodel,
oneoftheeffectivemediummodels[2,4],whichhasbeenwidelyusedtomodelacrackedrock.Figure9showsthetheoreticalcurvescalculatedbythismodelinthecross-plotoftheP-wavevelocityandporosity.Fourcurvesoverlaidontherealdataaretheoreticalonesforfourdifferentaspectratios,0.02,0.05,0.1and0.5ofthecracksin
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