WellControl-Lesson1FormationPressureDec.20041H.KhedersolhPressureConceptsThetwopressuresofprimaryconcernare:Formationpressure&Hydrostaticpressure.Formationpressure:istheforceexertedbyfluidsintheformation.-

Alsocalledreservoirpressure,&/or-Shut-inbottomholepressure.Dec.20042H.KhedersolhFormationPressure

TheoriginofF.P.:Itrelatestohowsedimentarybasinsareformed.Aslayeruponlayerofsedimentsaredeposited,overburdenpressureonthelayersincreases,&compactionoccurs.Soanyfluidsintheformationaresqueezedintopermeablelayers,suchassandstone.Ifthepermeablelayeriscontinuoustothesurface(outcropsonthesurface)pressurehigherthannormalcannotform.Butifthefluidistrappedbecauseofsomeanomaly,pressurehigherthannormalcanform.

Dec.20043H.KhedersolhFormationPressureNormalpressureSubnormalpressure-AbnormalpressureDec.20044H.KhedersolhHydrostaticPressure

Thetermisderivedfrom“hydro”,meaningwaterorliquid,&“static”,meaningatrest.Hydrostaticpressurereferstothepressureofdrillingfluidinthewellbore.Dec.20045H.KhedersolhHydrostaticPressure

Inthewellbore,H.P.istheresultofthefluiddensity&trueverticaldepthofthefluidcolumn.Dec.20046H.KhedersolhHydrostaticPressureWhere:C=0.052,ifmuddensityisexpressedintermsofppg,&C=0.00695,ifmuddensityisexpressedintermsofpcf.Dec.20047H.KhedersolhMudgradient

Pressure&mud

gradientistheamountpressurechangeswithdepth.Itisobtainedbymultiplyingthemudweightbytheconstant.MG=MW×C0.0520.00695Dec.20048H.KhedersolhMudgradientPressureormudgradientisobtainedbymultiplyingmudweightbytheconstantC.So,thegradientfora12ppgmudis:MG=12×0.052=0.624psi/ftDec.20049H.KhedersolhMudgradientEX.Thehydrostaticpressureofamudwith0.624psi/ftgradientina11,325ftwellwouldbe,HP=0.624×11,325HP=7067psiDec.200410H.KhedersolhMudgradientNormalpressuregradientscorrespondtothehydrostaticgradientofafreshwaterwithadensityof8.33ppg(0.433psi/ft)to9.0ppgsalinewater(0.465psi/ft)column.Dec.200411H.KhedersolhMudgradientDec.200412H.KhedersolhTYPICALGRADIENTFORS.IRANGRADIENTPSI/FTFormationPorePres.MudPres.Frac.P.Aghajari0.4330.4500.68Mishan0.4650.4790.70Gs.(7)0.4650.500.78Gs.(6-1)0.8-1.00.85-1.101.1Asmari0.24-0.490.433-0.560.74Pabdeh0.5-0.540.52-0.560.81Gurpi0.5-0.540.52-0.560.83Ilam0.540.560.74Sarvak0.540.560.74Fahliyan0.540.560.79Dec.200413H.KhedersolhPressureGradientEx.Drawthelinesofpressuregradients(pore,mud&fracture)forAj.toAs.formationsbasedontableofdatainpreviousslide.Correlateitwithlithology&stratigraphiccolumn.

Dec.200414H.KhedersolhPressure

GradientFracturepressureAreaofLostCirculation0.5ppgSafetymarginPorepressureKickareaBHPlessthanformationpressurecausesthewelltoKick,&greaterthanfracturepressurecauseslostreturn.

Dec.200415H.KhedersolhMudgradientNormalpressuregradient:about0.433-0.465psi/ft.Thegradientslessthan0.433psi/ft&greaterthan0.465psi/ftareknownassubnormal&abnormal,respectively.

Dec.200416H.KhedersolhMudgradientPressure,psiDepth,ftSurfacePressuregradient=0.433psi/ftPressuregradient=0.465psi/ftSubnormalAbnormalDec.200417H.KhedersolhAnnularPressureLossAnnularpressure,thepumppressurerequiredtomovemuduptheannulus,mustbeconsideredinwellcontroloperations.Thispressureislessthan200psiatthereducedpumpspeedsusedinkillingawell.Dec.200418H.KhedersolhAnnularPressureLoss

Whenmudisbeingcirculated,bottomholepressureequalshydrostaticpressureplusthepressurerequiredtomovemuduptheannulus.Annularpressurelossexistsonlywhenmudisbeingcirculated&itceaseswhenthepumpisstopped.Dec.200419H.KhedersolhFlowPathH.Khedersolh20Dec.200420H.KhedersolhAnnularPressureLoss

TheamountofAPLdependsonwhetherthemudflowintheannulusislaminarorturbulent.Dec.200421H.KhedersolhAnnularPressureLossAPLishigherwhenthemudisinlaminarflow.Flowintheannulusisusuallylaminar,becausethemudvelocityintheannulusduringwellcontroloperationsisdecreasedbyloweringthepumpspeedbelowthespeedusedfornormaldrillingoperations.

Dec.200422H.KhedersolhAnnularPressureLoss

APLinlaminarflow:Dec.200423H.KhedersolhAnnularPressureLossEx.CalculateAPLaccordingtodata’savailableL=16,000ft(TVD),YP=8lb/100ft2,PV=24cpV=1.2ft/sec,Dh=8.5in.,Dp=4.5in.APL=(16,000×8)/225(8.5-4.5)+(16,000×

24×

1.2)/1,500(8.5-4.5)2=(128,000/900)+(460,800/24,000)=142.2+19.2=161.4psiDec.200424H.KhedersolhEquivalentCirculatingDensity

AnotherwaytolookattheBHPincreaseduetofrictionlossesintheannulusisintermsofECD.ECDisacombinationoftheoriginalmudweightplustheequivalentmudweighti