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ID:32505905
大小:272.50 KB
页数:11页
时间:2019-02-09
《【7A文】钻井工程英文课件1.12 Wellbore Stability.ppt》由会员上传分享,免费在线阅读,更多相关内容在工程资料-天天文库。
1、1WellboreStability1.12-11.12-2FailureModesTensileFailureShearFailureMatrix/PoreCollapse1.12-3SymptomsThewellboremaysloughbecauseInitiationand/orextensionofhydraulicfracturesLocalmobilizationofpre-existingfaults.Suddenspallingmayoccurduringswabbingortripping.Dragforcesmaycauserapidsandproduc
2、tion.Ductileformationssuchassalt,otherevaporitesandsoftshalescansqueezeandrestrictthehole.Certainshalescanswell.1.12-4ShaleStabilityCanbeeffectedby:ExposuretimeFiltratechemistryIonictransportDehydration(duringUBD)1.12-5ShaleStabilityThetwomostrelevantmechanismsare:thehydraulicpressurediffer
3、encebetweenthewellborepressureandtheshaleporefluidpressureChemicalpotentialdifferencesbetweenthedrillingandshaleporefluids.1.12-6SmectiticShalesDuctileandcreepReducedwellborepressureacceleratescreepChemicallysensitivetomudfiltrate’sionicstrengthImbibitioncanoccurwithsubsequentswelling,andsh
4、oughing1.12-7SmectiticShalesSalt,gilsoniteorpolymerscanbeaddedtothemudtostabilizethesetypesofshales.1.12-8IlliticShalesHigherquartzcontentandusuallymorestablethatSmectiticshalesFrequentlymorebrittleandinert.However,massivefailurecanoccurduringhighpressuredrawdownduetothebrittlenessandstored
5、energywithintheporefluids.1.12-9FailureCriteriaVonMisesTrescaMohr-CoulombDruker-PragerHoekandBrown1.12-10Mohr-Coulombt=co+sn¢tanft.........shearstress(one-halfofthedifferencebetweenthemaximum,andminimumprincipalstresses)sn¢......effectivenormalstress(averageofthemaximumandminimumeffectivepr
6、incipalstresses)co........cohesion(interceptonat-sn¢plot),and,f.........angleofinternalfriction(angleofMohr-Coulomblocusfromthesn¢axisonat-sn¢plot).1.12-11MinimumTolerablePressures
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