阿美井控

阿美井控沙特技术培训系列(五)12SECTIONA基本压力概念UnderstandingPressures2UnderstandingPressures3HydrostaticPressureThemagnitudeofthehydrostaticpressureisdeterminedbytheheightofthecolumnoffluidandthedensityofthefluid.EquationHydrostaticPressure(HP)=MWx0.007xTVDwhere:HP=HydrostaticPressure(psi)MW=MudWeight(pcf)TVD=TrueVerticalDepth(ft)Remark:TVD&TDBothliquidsandgasescouldexerthydrostaticpressure.UnderstandingPressures4PressureGradientThepressuregradientassociatedwithagivenfluidissimplythehydrostaticpressureperverticalfootofthatfluid.EquationPressureGradient（PG）=MWx0.007where:PG=PressureGradient(psi/ft)MW=MudWeight(pcf)Remark:Pressuregradientcanbethoughtofasanalternatewayofdescribingafluid’sdensity.UnderstandingPressures5FormationPressureFormationpressureisthepressurecontainedinsidetherockporespaces.Iftheformationpressureisgreaterthanthehydrostaticpressureofthemudcolumn,fluids(gas,oilorsaltwater)canflowintothewellfrompermeableformations.SurfacePressureSurfacepressuremaybegeneratedfromavarietyofsourcesincludingdownholeformationpressures,surface-pumpingequipment,orsurfacechokes.Circulatinganopenwellwith1,000psipumppressurewillnotincreasethebottomholepressureby1,000psi.Theannularfrictionlossgeneratedwhilecirculatingwillincreasethebottomholepressurebutwillnotincreasetheannularsurfacepressure.Uderstaticconditions,anypressurewhichweobserveatsurfacewillalsobeconveyeddownhole.UnderstandingPressures6BottomholePressureBottomholepressureisequaltothesumofallpressuresactinginawell.EquationBHP=HP+SP+FPwhere:BHP=BottomholePressure(psi)HP=HydrostaticPressure(psi)SP=SurfacePressure(psi)FP=FrictionPressure(psi)Remark:Ifcirculatingthroughachokeorseparatoratthesurface,theannularsurfacepressureandfrictionpressure(backpressures)willbeconveyeddownholeandmustbeaddedtothemudhydrostaticpressuretoobtainthetotalbottomholepressure.Ifthewellisshutin,understaticconditions,thebottomholepressurewillbeequaltothesumofthehydrostaticpressureandanyobservedsurfacepressure.UnderstandingPressures7EquivalentCirculatingDensityTheannularfriction,orannularpressurelossasitissometimesreferredto,actsagainstthebottomofthewellbore,whichresultsinanincreaseinbottomholepressure.ThisisknownasEquivalentCirculatingDensity,orECD.EquationECD=TotalAnnularPressureLoss/(0.007xTVDhole)+PresentMudWeightRemark:Calculationwhendifferentmudweightexistinannular.Calculationwhenbackpressureexist.FracturePressureFracturepressureistheamountofboreholepressurethatittakestosplitorfailaformation.8SECTIONB溢流的原因CAUSESANDDETECTIONOFKICKS2CausesofKicks9DEFINITIONAkickisdefinedasanyundesirableflowofformationfluidsfromthereservoirtothewellbore,whichoccursasaresultofanegativepressuredifferentialacrosstheformationface.Wellskickbecausethereservoirpressureofanexposedpermeableformationishigherthanthewellborepressureatthatdepth.CAUSESofKICKS:LowDensityDrillingFluidAbnormalReservoirPressureSwabbingNotKeepingtheHoleFullonTripsLostCirculationCausesofKicks10LowDensityDrillingFluidA.Thedensityofthedrillingfluidisnormallymonitoredandadjustedtoprovidethehydrostaticpressurenecessarytobalanceorslightlyexceedtheformationpressure.B.Accidentaldilutionofthedrillingfluidwithmakeupwaterinthesurfacepitsortheadditionofdrilled-up,lowdensityformationfluidsintothemudcolumnarepossiblesourcesofadensityreduction.C.Mostwellsaredrilledwithsufficientoverbalancesothataslightreductioninthedensityofthemudreturnswillnotbesufficienttocauseakick.D.Densityreductionscausedbygascuttingandthosecausedbyoilorsaltwatercuttingmustbedistinct.CausesofKicks11GasCutting①Gasisverycompressibleandaverysmallvolumeofgashasaninsignificanteffectonmuddensitydownhole,.②Thehydrostaticpressureofthegasinacuttingisgreatlyreducedasitmovesuptheannulus,allowingthegastoexpandandenterthemudcolumn.Whilenearthesurface,smallvolumeofgaswouldhaveexpandedmanytimesresultinginapronouncedreductionofsurfacedensity③Inabalancedorslightlyoverbalancedcondition,gasoriginatingfromcuttingscouldreducethebottomholepressuresufficientlytoinitiateakick.Gradualincreasesinpitlevelwouldbeobservedatfirst,butastheinfluxofgascausedbytheunderbalancedconditionarrivesatthesurface,rapidexpansionandpitlevelincreasewilloccur.④Whengascutmudcausesahydrostaticpressurereductionlargeenoughtoinitiateakick,thedensityofthemudbeingpumpeddownholewillusuallynothavetobeincreasedtokillthewellCausesofKicks12AbnormalReservoirPressureFormationpressureisduetotheactionofgravityontheliquidsandsolidscontainedintheearth'scrust.Ifthepressureisduetoafullcolumnofsaltwaterwithaveragesalinityforthearea,thepressureisdefinedasnormal.Ifthepressureispartlyduetotheweightoftheoverburdenorfaultingandisthereforegreater,thepressureisknownasabnormal.Pressuresbelownormalduetodepletedzonesorlessthanafullfluidcolumntothesurfacearecalledsubnormallypressured.CausesofKicks13SwabbingA.Swabbingisacondition,whichariseswhenpipeispulledfromthewellandproducesatemporarybottomholepressurereduction.B.Themostreliablemethodofdetectionisproperholefilling.Ifalengthofdrillpipecomposedoffivebarrelsofmetalvolumeispulledfromthewellandtheholefill-u