Drillstring Design.docx
DrillstringDesignA. WeightofDrillpipeandBHAbasedonWOBBottomholeassembly(BHA)isthepartofthedrillstringwhichisjustabovethebitandbelowthedrillpipe.Itusuallyconsistsofdrillcollars,stabilizersandvariousothercomponentsincludingjar,heavyweightdrillpipe,etc.DrillbitandBHA(bottomholeassembly)datacontainedonthesewellareasfollows:Bit12l4nBit1214,Bit8l2ManufacturerRockBitHycalogManufacturerPDCHycalogManufacturerPDCHycalogSerialNumber1619-103324SerialNumber123121SerialNumber124031Nozzle3x16Nozzle5x18Nozzle5x16Length(ft)0,95Length1,02Length0,72BitSub(ft)3BitSub3BitSub3lx8DC(ft)30,441JTS8"DC30,441x612,'DC30,65121/4"STB(ft)5,78XO5,78XO1,645x8DC(ft)152,535JTS8"DC152,53812,'STB5,58x/o(ft)1,6XO1,6XO1,64lx5,'HWDP(ft)30,85lx5HWDP30,8511x61/2"DC337,55x/o(ft)1,63XO1,63lx5,'HWDP30,85614hJAR(ft)32,8461/4"JAR32,5XO1,63x/o(ft)1,6XO1,661/4"JAR32,515x5"HWDP(ft)462,0415x5nHWDP462,04XO1,615x5"HWDP462,04TotalBHA(ft)532,91TotalBHA(ft)722,99TotalBHA(ft)909,4WOB(lbftx1000)5sampai10WOB(lbftx1000)4sampai7WOB(lbftx1000)5sampai10Table9.1AndparametersofthedrillbitisusedforthedepthintervalofthewellcanbeseeninthetablebelowSectionBitDataNozzleDepthInterval(ft)WOB(klbs)1RR121/4”RockBitS/N1619-1033243x16572-12085-10RR121/4”PDCS/N1231215x181208-18744-72RR812''PDCS/N1240315x181874-36105-10Table9.2Thependulumprinciplewasoriginallyusedtodrillverticalwellswithslick(nonstabilised)BHAs.ThephysicalpropertiesofthevariousdownholecomponentsoftheBHAhaveasignificanteffectonhowthebitwilldrill.TheprincipleusestheweightoftheBHAhangingbelowthetangentpointtoproduce,viagravity,aforcethatpushesthebittothelowsideofthehole.TheeffectofthependulumvarieswiththelengthoftheBHAbelowthetangentpoint.Thefundamentalpendulumassemblyincreasestherestoringforcebyincreasingthependulumlengthwithastabiliserintheproperposition.Whenthedrillstringisloweredintotheborehole,thetotallengthofthedrillstringisundertensionduetoitsownweightwhichispartlycounterbalancedbythebuoyancy.Todrillawell,therockbeneaththebithastobedestroyed.Partofthisdestructionforceisobtainedbyacertainamountofweightonbit(WOB)whichforcesthebitagainsttherock.Thereforeduringdrilling,thelowerpartofthedrillstringissetundercompression,leavingtheupperpartofitstillundertension.Whendrillingverticalwells,standardpracticeistoavoidputtingordinarydrillpipeintocompression(recommendedbyLubinskiin1950).Thisisachievedbymakingsurethatthetbuoyedweighf,ofthedrillcollarsandHWDPexceedthemaximumWOB.Thebuoyedweightofthedrillcollarsistheamountofweightthatmustbesupportedbythederrickwhencollarsareruninthehole.Thisloadisalwayslessthanthein-airweightifmudisusedinthewell.Thehighertheweightonbit,themoretheassemblywillbend.Thiscanmovethetangentpointnearertothebitandhenceisdetrimentaltotheeffectivenessoftheassembly.Furthermore,thesideforceatthebit,producedbytheweightonbit,actsagainstthependulumforce.Weightonbitaslowaspossibleisdesirableforapendulumassembly.WOBdataareavailableforeachtypeofbitsfromthiswell,wecandeterminetheweightofBHAminimuminairusingtheformulabelow.Requiredair weight of BHA9.1MaximumWOBxsafetyfactorbuoyancyfactorxcoswherethesafety factor = 1 +percentagesafety margin1009.2andTheBF(buoyancyfactor),assumingthatthedrillstringisnotloweredempty(PSteel=655ppg),canbecomputedas:BF=(I-")9.3Psteel/Thenormaldrillstringdesignpracticeaimistoavoidabruptchangesincomponentcrosssectionalareas.Abruptchangescanleadtoconcentrationsinbendingstresseswhichinturncanleadtoatwistoff(Refertofigure9.1).TheratioI/Cbetweenthemomentofinertia(I)andradius(C)ofthepipeisdirectlyrelatedtotheresistancetobending.ThefollowingareusedtodeterminethesectionmodulusI/C:I=Momentofinertia9.4=x(OD4-1D4)C=-Radiusofthetube9.564_OD-2Atacrossoverfromonetubularsizetoanothersize,theratio(I/Clargepipe)(ICsmallpipe)shouldbelessthan5.5forsoftformationsandlessthan3.5forhardformations.d. _ I/C Drill Collars KatIO =.I/C Drill Pipes9.6Drillpipewillbesubjectedtoseriousdamageifrunincompression.Tomakesurethetension.Thisgivesasafetymarginandkeepsthebuoyancyneutralpointwithinthecollarswhenunforeseenforces(bounce,holefriction,deviation)movethebucklingpointupintotheweakerdrillpipesectionorthiswillputthechangeoverfromtensiontocompression,orneutralzone,downinthestiffdrillcollarstringwhereitisdesirableandcanbetolerated.AccordingtoLubinski,theneutralpointisdefinedaspointalongthedrillstringwhereitisdividedintotwoparts,anupperpart,beingsuspendedfromtheelevatorsandwhichisundertensionaswellasalowerpartthatgeneratestheappropriateWOBandisundercompression.Sincethecollarsareundercompression,theywilltendtobendundertheappliedload.Theamountofbendingwilldependonthematerialandthedimensionsofthecollar.Theshapeofthedrillcollarmayhaveacircularorsquarecrosssection.Astringofsquarecollarsprovidesgoodrigidityandwearresistance,butitisexpensive,hashighmaintenancecostsforcertainconditionsandmaybecomestuckinkey-seateddog-leg.Typically,standardandspiraldrillcollarswithexternalgroovescutintotheirprofilemaybeusedtoreducethecontactareabetweentheBHAandtheformation.Usingequation9.3andthedataofthemudusedinthesewellsareshowninTable9.3,theobtainedBF(buoyancyfactor)inTable9.8.Depth(ft)MudWeight(ppg)YieldPoint(lb100ft2)5728,7109538,810119091211989,21318709,21418779,2825699,31129839,41231599,41434579,414Table9.3FortheportionofpendulumBHAbelowthetangentpointorfirstdrillstringstabiliser,itisdesirabletorundrillcollarswiththelargestpossibleoutsidediameter.Butpotentialproblemsassociatedwithfishingthedrillcollarsmustbeconsideredinthedesignstage.Duetolackofdata,theselectionofdrillpipewithasizeof5"ODanddrillcollar8"ODbasedonthetablebelowfromENlwhichillustratesthepossibilityandacceptabilityfor121/4uholeofsoftformations.Holesize(in)Drillcollar/DrillpipeI/CI/CRatioRemarks12l4uDC912,'x3"83,81,5OKforsoftformationsDC81/4"x213/16"55,95,2HWDP5"x42.6lbft10,71,9DP5"x19.5lbft5,7-Table9.4Hereisthedimensionaldataandperformancepropertiesofnewdrillpipe5"ODfromAPIRP7GOD(in)Weight(1bft)ID(in)WallThickness(in)SectionAreaBodyofPipe(sq.in)GradeTorsionalYieldStrength(ft.lb)TensileYieldStrength*(Ib)CollapsePressure(PSi)BurstPressure(PSi)Approx.Wt.IncLTube&Joint(Ib)PlainEnd516,2514,874,4080,2964,3743E35.040328.0706.9407.770X-9544.390415.5608.1109.840G-10549.060459.3008.62010.880S-13563.080590.5309.83013.99019,517,934,2760,3625,2746E41.170395.60010.0009.960X-9552.140501.09012.03012.040G-10557.600553.83013.00013.300S-13574.100712.07015.67017.110Table9.5Thereforechosendrillpipesize5“x3”anddrillcolarsize8"x3”.ProvedbycalculatingtheratiooftheI/Catacrossoverfromonetubularsizetoanothersizebyusingequation9.6,itsvalueislessthan5.5.Drillcollar/Drillpipe(in)I/CI/CRatioRemarksDC8”X3”49,34,607476636BetweenDCandHWDPHWDP10,71,877192982BetweenHWDPandDPDP5"x4.276”5,7-Table9.6Thereisheavyweightdrillpipeonbottomholeassembly,thedimensionaldataandperformancepropertiesofHWDPfromthedrillingdatabookofBakerHugescompanycanbeseeninthetable9.7.Nomsize(in)TUBEWeightNom.TubeDim.UpsetSec.Perform.Prop.Approx.Wt.IncLTube&Joint(Ib)ID(in)WallThick,(in)Center(in)Ends(in)TensileYield(Ib)Torsional(ft.lb)RangeIIRangeIIIlbftlbjt30ftlbftlbjt45ft31/221/160,719435/8345.40019.53526810-429/160,71941/241/8407.55028.74528870-41/223/40,875545/8548.07540.62542129040174553151/251/8691.18556.365501550482090Table9.7Usingequation9.1andequation9.3withasafetymarginof10%gainedweightdrillpipeandBHAareshowninthefollowingtableIntervalDepth(ft)MWrata-rata(ppg)BFMaxWOB(IbfxlOOO)RequiredairweightofBHA(Ib)LBHA(ft)LDP(ft)WDPinair(Ib)572-12088,980,8629007631012747,69993532,91675,0913164,2551208-18749,20,85954198578958,259325722,991151,0122444,6951874-36109,3285714290,8575790621012826,8057909,42700,652661,7Table9.8ThelengthofdrillpipeintheabovetableisobtainedusingthefollowingformulaLDP=DepthLBHA9.7WhiletheweightofdrillpipeobtainedusingtheformulabelowWdpinair=LdpxAPIapproximateweight9.8B. ChartofTensionandCompressionalongDrillstringThetensionloadisevaluatedusingthemaximumloadconcept.Thetensionloadcanbeevaluatedaftertheweights,grades,andsectionlengthshavebeenestablishedfromthecollapsedesigns.Buoyancyisincludedinthedesigntorepresentrealisticdrillingconditionsduetothemannerinwhichbiaxialstressesalterthecollapsepropertiesofthepipe.Thetensiondesignisestablishedbyconsiderationofthefollowing:1. TensileForces:Theseinclude: weightcarried shockloading bendingforces2. Designfactor3. SlipCrushingDesignThetensiondesignlineisestablishedasthemaximumloadresultingfromapplyingthreedifferentdesignconsiderations,includingoverpull,designfactors,andslipcrushing.Eachconsiderationisappliedseparatelytotheloadline.Thedesignlineisselectedastheworstcasefromthethreedesignloads.Aminimumoverpullfactorisappliedtothetensionload.ThedifferencebetweenthemaximumallowabletensionandthecalculatedloadrepresentstheMarginofOverPull(MOP).MOPistheminimumtensionforceaboveexpectedworkingloadtoaccountforanydragorstuckpipe.TheminimumrecommendedvalueofMOPis60.000Ibanditshallbecalculatedforthetopmostjointofeachsize,weight,gradeandclassificationofdrillpipe.TheanticipatedtotaldepthwithnextstringrunandexpectedmudweightshouldbeconsideredwhencalculatingtheMOP.Atypicalrangefortheoverpullvalueis50.000-100.000lb.WhendecidingonthemagnitudeoftheMOP,thefollowingshouldbeconsidered: Overalldrillingconditions Holedrag Likelihoodofgettingstuck(mayrequirehighervaluesofMOP)WhenthedepthisreachedwheretheMOPapproachestheminimumrecommendedvalue,strongerdrillpipeshallbeaddedtothestring.Arangeoftensiondesignfactorshasbeenfrequentlyusedfordrillpipedesign.Thisrangeistypicallyfrom1,1-1,5although1,1-1,3seemstobemostcommon.Adesignfactorof1,6shouldbeappliedtothetensionloadscalculatedaboveifshockloadingisnotaccountedfor.Theprimarypurposeofthedesignfactoristoensureanoverdesignofthepipetominimizethecatastrophicproblemofpipepartingnearthesurfacewhenthepipeisfullyloaded.Inaddition,itisselectedtoaccountforaccelerationloadingofthepipe,whichoccurswhentheslipsareset.Themaximumallowabletensionloadmustalsobedesignedtopreventslipcrushing.Inananalysisoftheslipcrushingproblem,ReinholdandSpini,andalsoVreeland,proposedanequationtocalculatetherelationbetweenthehoopstress(Sh)causedbytheactionoftheslipsandthetensilestressinpipe(ST)resultingfromtheloadofthepipehangingintheslips.Theequationsusedareasfollows:TS=TL僵)9.9WhereTs=TensionloadduetoslipcrushingTs=Staticloadtension(ShSt)ishoopstresstotensionstressratioasderivedfromtheequationbellow:()=(÷÷o2加。WhereSh=Hoopstress(psi)S=Tensilestress(psi)D=OuterDiameterofthepipe(in)K=Laterloadfactoronslips(y-r)htan(y+z)/y=Sliptaper(typically9o2745"or9,4625degrees)z=Arctan=Coefficientoffriction,typically0,06-0,14Ls=Lengthofslips,usually12-16inInasmuchastooljointlubricantsareusuallyappliedtothebackofrotaryslips,acoefficientoffrictionof0.08shouldbeusedformostcalculations.Tocreateagraphoftensionandcompressionalongthedrillstringrequiresthefollowingcalculation.1. Calculatethebuoyancyforce(BFl)actingonthebottomofthedrillcollarsusing:BFl=一(PXA)9.11P=0,052xDepth(ft)xMudWeight(PPg)X：(ODDCi)2一(IDDC>n)29.122. Calculatethebuoyancyforce(BF2)actingatthetopofthedrillcollars.BF2=(PxA)9.13Duetothewelldrillstringconsistsofdrillcollar,HWDP,anddrillpipethentheformulausedtocalculatePisasfollows.P=0,052XLDPXMWXt(ODdc)2-(ODdp)29.14+0,052x(Depth-Ldc)xMWxj(ODdc)2一(ODHWDP)?+0,052xLdpxMWx:(IDdp)2-(IDdc)23. Calculatethedrillcollarweight=x(0Din)2-(IDin)2)xlftx(489,5%)x击WDCinair(Ib)=WDCinair电XLDC9.164. CalculatetheshockloadShockload(Ib)=1500Xpipeweightperfoot9.17Note:1500wasusedtorepresentslowrunningspeeds.5. CalculatethetotaldynamicandstaticloadatsurfaceTotaldynamicload(Ib)=BFl+BF2+drillcollarweight+drillpipeweight+shockload9.18Staticloadwithoutshockload(Ib)=BFl+BF2÷drillcollarweight+drillpipeweight9.196. Staticloadattopofdrillcollars(Ib)=BFl+WDCinair9.207. Staticloadatbottomofdrillpipe(Ib)=BF2+Staticloadattopofdrillcollars9.218. Dynamicloadatbottomofdrillpipe(Ib)=Staticloadatbottomofdrillpipe÷shockload9.229. Calculatethedesignlineforthetensionloadbymultiplyingtheloadonthedrillpipeatsurfaceandatthetopofthecollarsbythe1,3designfactor(sinceshockloadshavebeenincluded).10. CalculatethedesignlinefortheMOPbyaddingthe50.000-100.000Iboverpullfactortothestatictensionloadvaluescalculatedearlier.11. Calculatethedesignlineforslipcrushingusingequation9.9andequation9.10withTL=staticloadatsurfacewithoutshockload.AssumesproductiontestzoneorDST(DrillStemTest)packerdepthwasjustabovetheBHA,thedesignfactorof1.3forthetension.Fortheintervaldepth572-1208ftMOP100.000Ibandfortheinterval1208-3610ftMOP60.000lb.Usingequationsabove,obtainedthefollowingStatic&dynamicloadsandcompletetensiondesigngraphalongthedrillstringforeachtypeofbitandBHAused.Theresultsofthecalculationscanbeseeninthetable9.9,9.10,and9.11BitDataTensionLoadLineDrillcollarweight(Ib)DrillpipeWeight(Ib)HWDPweight(Ib)Shockload(Ib)Bouyantforceactingonthetopofthecollars/BFl(Ib)Bouyantforceactingonthetopofthecollars/BF2(Ib)RR12l4uRockBitS/N1619-103324-24366,8385326490,2868928156,4662113164,25525390,0829250RR1214,PDCS/N123121-38726,9529945532,7516728156,4722439,4325450,5629250RR81/2”PDCS/N124031-75644,6569597670,9126255807,856291,4325373,7629250Table9.9BitDataTotaldynamicloadatsurface(Ib)Staticloadatsurfacewithoutshockload(Ib)StaticloadattopofdriHcolIars(Ib)StaticloadatbottomofDP+HWDP(Ib)DynamicloadatbottomofDP+HWDP(Ib)RR121/4”RockBitS/N1619-10332498084,2495668834,24963789,62767530279,9145659529,91456RR121/4”PDCS/N123121112102,254982852,25488-10570,4867934962,2648864212,26488RR812''PDCS/N124031188749,2503159499,2503-19836,8522777834,06035107084,0603Table9.10BitDataDesignlinetensionloadDesignlineforMOPDesignlineforslipcrushingTotalDynamicloadatsurface(Ib)DynamicloadatbottomofDP+HWDP(Ib)Staticloadatsurfacewithoutshockload(Ib)StaticloadatbottomofDP+HWDP(Ib)SH/STSlipcrushingloadatsurface(Ib)SlipcrushingloadatbottomofDP+HWDP(Ib)RR121/4"RockBitS/N1619-103324127509,52477388,8889168834,25130279,9151,29957257989455,1032539350,94667RR12l4nPDCS/N123121145732,931483475,94435142852,25594962,26491,29957258107672,5
