1 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben PETROLEUM ENGINEERING SUMMER COURSE2015 "#$%&'#() *+,-+##%-+, .#/-,+ "012 0 .%-''-+, *+,-+##%-+, 340"2*1 5 6&%)78&+ "%&9#%8#/ 37/-+, :#;+, .#9$< 2 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben 8ocks LarLh CrusL ls composed essenually of 3 Lypes of rock: 1.lgneous 2.MeLamorphlc 3.SedlmenLary (assoclaLed wlLh oll & gas) -SandsLone -Shale -CarbonaLes -uolomlLes 3 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. It is characterized by thin laminate breaking with an irregular curving fracture, often splintery and usually parallel to the often-indistinguishable bedding plane. This property is called fissility. Non-fissile rocks of similar composition but made of particles smaller than 1/16 mm are described as mudstones. Rocks with similar particle sizes but with less clay and therefore grittier are siltstones.eLroleum Mlgrauon Pydrocarbons have lower denslLy Lhan Lhe waLer lllng Lhe pores of Lhe sedlmenLary rock. 1hls causes Lhe hydrocarbons generaLed ln Lhe source rock Lo rlse upward. 1hls Lype of mlgrauon occurs ln porous, permeable rock formauons and Lhrough cracks and ssures (faulLs). Cnce Lhe ascendlng oll or naLural gas reaches a locauon where porous rock meeLs wlLh lmpermeable rock (usually some form of clay) and forms a 'Lrap', Lhe 'Lrapped' hydrocarbons are prevenLed from escaplng, and a deposlL ls formed. 4 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben eLroleum Mlgrauon Pydrocarbons have lower denslLy Lhan Lhe waLer lllng Lhe pores of Lhe sedlmenLary rock. 1hls causes Lhe hydrocarbons generaLed ln Lhe source rock Lo rlse upward. 1hls Lype of mlgrauon occurs ln porous, permeable rock formauons and Lhrough cracks and ssures (faulLs). Cnce Lhe ascendlng oll or naLural gas reaches a locauon where porous rock meeLs wlLh lmpermeable rock (usually some form of clay) and forms a 'Lrap', Lhe 'Lrapped' hydrocarbons are prevenLed from escaplng, and a deposlL ls formed. "&%&/-$= 7+> "#%)#7?-'-$= 3 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben MaLrlx uenslues (!m) of 1yplcal 8eservolr 8ocks Lithology Matrix Density(g/cm3) Sandstone2.65 Limestone2.71 Dolomite2.87 1hese values are lmporLanL for core and log analysls.CommlL Lhem Lo memory. unforLunaLely, few rocks conslsL of pure componenLs buL exlsL as a mlxLure of numerous mlnerals of varylng slzes and composluons.1herefore, one can rarely assume Lhe maLrlx denslLy and geL an accuraLe esumaLe of maLrlx volume. 8ock MaLrlx and ore Space @7$%-A non pore space: gralns of sandsLone, llmesLone, dolomlLe,and/or shale ore space: lled wlLh ulds: formauon waLer, oll, and/or gas 6 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben oroslLy:1he fracuon of a rock LhaL ls occupled by pores and lled wlLh uldPorosity =! = VporesVbulk= Vbulk !VgrainVbulk"bulk = "grain(1!!) + "fluid! "! = "grain ! "bulk"grain ! "fluidoroslLy uenluon -oroslLy ls a sLauc properLy - lL can be measured ln Lhe absence of ow -ueLermlnlng eecuve poroslLy requlres uld ow Lo deLermlne lf pores are lnLerconnecLed AbsoluLe and Lecuve oroslLy AbsoluLe and eecuve poroslLy are dlsungulshed by Lhelr access capablllues Lo reservolr ulds. ermeable spaces conLrlbuLes Lo eecuve poroslLy vold spaces conLrlbuLes Lo absoluLe poroslLy 6'(-> B&C -+ D7%?&+7$# E7%/$ %#/#%F&-%/ 7 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben 1ypes of oroslLy 8ock medla havlng boLh fracLure and lnLer-granular pores are calleddouble-porous or fracLure-porous medla. G+$#%H,%7+('7% 6%7D$(%#> I(,('7%G+$%7H,%7+('7% 8ulk uenslLy Change Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 1he change ln bulk denslLy wlLh burlal depLh ls relaLed prlmarlly Lo Lhe change ln sedlmenL poroslLy wlLh compacuon. ln many areas an exponenual relauonshlp relaung change ln average sedlmenL poroslLy Lo depLh ls used: 8 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben oroslLy uecllne ConsLanL Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 ermeablllLy 1he permeablllLy of a rock ls a measure of how easlly a ulds may ow Lhrough Lhe pore channels ln a rock. lL depends on Lhe slze, shape, LorLuoslLy and number of Lhe pore channels ln Lhe porous medlum. AbsoluLe permeablllLy ls Lhe permeablllLy of Lhe porous medlum lf a slngle uld ls owlng.Lecuve permeablllLy ls Lhe permeablllLy of a uld lf anoLher uld ls presenL.8elauve permeablllLy ls Lhe eecuve permeablllLy dlvlded by Lhe absoluLe permeablllLy. 9 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben ermeablllLy - uarcys Law u Darcy velocity, cm/s q fluid flow rate, cm3/s A cross-sectional area, cm2 k permeability, D ! -viscosity, cp dp pressure differential, atm dx length of core, cm !"#$%&' = =dxdpkAqux[ ]223secsecmPa mm Pamp AL qk =!!"#$$%&'=lf horlzonLal llnear ow of an lncompresslble uld ls esLabllshed Lhrogh a rock sample of porouse maLerlal of lengLh - and a cross secuonal area !, Lhe Lhe permeablllLy of Lhe maLerlal ls dened: 1 uarcy = 10-12 m2 1 cp = 10-3 a.s J6&%)78&+K "%#//(%# 10 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben PydrosLauc ressure lormulas phyd = ! g h a =kg/m3 * m/sec2 * m = kg / (m sec2) = n/m2 MeLrlc unlLs: Cll lleld unlLs: phyd (psl) = 0,032 ! (lb/gal) h () 1 kg/m3 = 0,008 lb/gal 1 a = 1,4304L-4 psl, 1 bar = 1L3 a = 14,304 psl 1 m = 3,281 Pow Lo Lxpress lormauon ressures? AbsoluLe values: e.g. lormauon pressure of 320 bars ln 2300 meLers depLh ressure CradlenL (bar/m) for above example: LqulvalenL uenslLy (kg/m3) for above example: 320/2300 = 0,128 bar/m 320*1e3/9,81/2300 = 1304,8 kg/m3 11 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben lmporLanL ressures ln urllllng lormauon pore pressure: ressure of Lhe ulds ln Lhe pores of Lhe rock lracLure pressure: ressure needed Lo fracLure Lhe rock (Pydro)sLauc pressure of Lhe drllllng uld: ressure of Lhe drllllng uld under sLauc condluons aL any depLh lrlcuon pressure losses: ressure dlerence needed Lo clrculaLe Lhe drllllng uld Lhrough any Lwo polnLs ln Lhe clrculauon sysLem ump pressure: Sum of all frlcuon pressure lossesSLandplpe pressure: Sum of all frlcuon pressure losses excepL Lhe surface llnes uynamlc pressure: PydrosLauc pressure plus frlcuon pressure aL any polnL ln Lhe clrculaung sysLem LqulvalenL clrculauon denslLy: uynamlc pressure expressed ln denslLy-unlLs for pracucal reasons aL any polnL ln Lhe clrculaung sysLem Cverbalanced pressure: osluve value for dynamlc (or sLauc) pressure mlnus formauon pressure aL any polnL ln Lhe open hole underbalanced pressure: osluve value for formauon pressure mlnus dynamlc (or sLauc) pressure aL any polnL ln Lhe open hole lormauon ore ressure and lracLure 8eslsLance lormauon pore pressure and fracLure pressure - Lhe knowledge of how Lhese Lwo parameLers vary wlLh depLh ls exLremely lmporLanL ln plannlng and drllllng a well. Cnly under normal pressure condluons Lhe formauon pressure ls equal Lo Lhe hydrosLauc pressure of Lhe ulds occupylng Lhe pores (e.g.formauon waLer) or Lhe producL !.g.h. 1he fracLure pressure or formauon breakdown pressure ls Lhe pressure requlred Lo overcome Lhe wellbore sLresses ln order Lo fracLure Lhe formauon ln Lhe lmmedlaLe vlclnlLy of Lhe wellbore. normally, Lhe fracLure pressure wlll be hlgher Lhan Lhe formauon pressure. ln overbalanced drllllng pracuces Lhe hydrosLauc pressure of Lhe drllllng uld as well as Lhe clrculauon pressure should be ln beLween Lhese Lwo. Cnly lf Lhls requlremenLs are fullled, Lhe well can be drllled safely wlLhouL lnow from formauon ulds (e.g. gas klcks) and wlLhouL loss of clrculauon uld. 12 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben normal ressured Zones SlmplesL Model: Shallow sedlmenLs LhaL are lald down slowly.SedlmenLs are lnlually unconsolldaLed and un-compacLed. 1hey have hlgh permeablllLy and poroslLy. 1he seawaLer mlxed wlLh Lhese sedlmenLs remaln ln Lhe pores as welghL of Lhe overburden supporLs Lhe compacuon of Lhe solld gralns. 1he hydrosLauc pressure remalns Lhe orlglnal value, lf permeablllLy ow paLh exlsL from Lhe formauon Lo Lhe surface. llulds ln Lhe pores ln Lhls case do noL lnuence Lhe compacuon process and Lhe nal formauon of pore volume due Lo Lhe overburden pressure. llulds wlll be squeezed ouL from Lhe pores and follow Lhe way of lowesLreslsLance. normal pressure gradlenLs: WesL 1exas: 0.433 psl/ (1.0 SC), Culf of Mexlco: 0.463 psl/ (1.074 SC), norLh Sea: 0.432 psl/ (1.044 SC), WesL Afrlca: 0.442 psl/ (1.021 SC) Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 Abnormal ressured Zones 1erm abnormal formauon pressure relaLes Lo pressures greaLer Lhan Lhe hydrosLauc pressure. 1erm subnormal formauon pressure relaLes Lo pressures smaller Lhan Lhe hydrosLauc pressure. 8easons for abnormal formauon pressure: Compacuon eecL ulageneuc eecL ulerenual denslLy eecL lluld mlgrauon eecL Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 13 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Abnormal lormauon ressure Caused by Compacuon LecL lf no sumclenL permeablllLy communlcauons Lo Lhe surface exlsL. 1he pore waLer expand wlLh lncreaslng LemperaLure whlle pore space ls reduce by welghL of lncreaslng geosLauc load (overburden). ln general, pore volume wlll remaln greaLer Lhan ln Lhe case of communlcauon. Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 Compacuon LecL ore waLer expands wlLh lncreaslng burlal depLh and lncreased LemperaLure. ore space ls reduced by lncreaslng geosLauc load.normal formauon pressure can be malnLalned only lf a paLh of sumclenL permeablllLy exlsLs Lo allow formauon waLer Lo escape.Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 14 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Abnormal lormauon ressure Caused by ulageneuc LecL ulagenesls ls Lhe chemlcal alLerauon of rock mlnerals by geologlcal processes. Shales and carbonaLes undergo changes ln crysLalllne sLrucLure. Lxample: converslon of monLmorlllonlLe clays Lo llllLes, chlorlLes, and caollnlLe clays ln Lhe presence of poLasslum lons. Water is present in clays as free water and water of hydration (interlayer water). Pore water is lost during compaction, interlayer water still remains in the clay. After reaching temperatures of 200 -300F, dehydration of the monmorillonite releases the last interlayer water and illite is formed. Interlayer water becomes free water.The water of hydration in the last inter-layers has considerably higher density than the free water, and, thus, undergoes a volume increase as it becomes free water. If no permeability communication exists, release of last water inter-layer will result in pressure increase. Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+,lS8n 1-33363-001-4 Abnormal lormauon ressureCaused by ulerenual uenslLy LecL When Lhe pore uld presenL ln any non-horlzonLal sLrucLure has a denslLy slgnlcanL less Lhan Lhe normal pore pressure uld denslLy for Lhe area, abnormal pressure can be encounLered ln Lhe up-dlp poruon of Lhe sLrucLure. Cauuon ln slLuauons when a gas reservolr wlLh a slgnlcanL dlp ls drllled.Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 pWCC = !w g P pgas,Lop = !w g P - - !g g h WGCGasWaterNormal formationPressure up to hereP h As Lhe denslLy of gas ls slgnlcanL less Lhan Lhe pore waLer denslLy, Lhe pressure aL Lhe Lop of Lhe gas reservolr would only be sllghLly less Lhan aL WuC 13 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben ulerenual uenslLy LecL Lxample: Conslder Lhe gas sand shown ln llgure below, whlch was encounLered ln Lhe Culf CoasL area. lf Lhe waLer lled poruon of Lhe sand ls pressured normally and Lhe CWC ls aL a depLh of 3.000 , whaL mud welghL would be requlred Lo drlll Lhrough Lhe Lop of Lhe sand safely aL a depLh of 4.000 ? Assume Lhe average gas denslLy Lo be 0.8 lbm/gal. Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 Solution: 1.Pore pressure at gas/water contact is: 0.465 x 5000 = 2325 psi 2.The pressure in the gas zone at 4000 ft is: 2325 - 0.052 x0.8 x (5000 - 4000) = 2283 psi 3.This corresponds to a pressure gradient of2283 / 4000 = 0.571 psi/ft 4.The mud density to balance this pressure is 0.571 / 0.052 = 11 lbm/gal llulds Mlgrauon LecL 1he ow of ulds from a hlgh pressure Lo a low pressure zone ls called ulds mlgrauon. lL can lead Lo an unexpecLed abnormal hlgh pressure ln shallower formauons. Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 16 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben lormauon ressure redlcuon lormauon pressure predlcuon ls of mosL lmporLance for safeLy buL dlmculL Lo handle. ressure daLa musL be avallable as early as posslble. MeLhods are based on Lhe facL LhaL abnormal formauon pressure zones are less compacLed and have hlgher poroslLy (ulds ln Lhe pores are capLured and prevenLmore compacuon by Lhe overburden). A poroslLy dependenL parameLer ls measured and ploued as a funcuon of depLh. 1echnlques applled: redlcuve meLhods (correlauon of avallable daLa, selsmlc meLhods) MeLhods applled durlng drllllng verlcauon meLhods Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 lormauon ressure redlcuon Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 17 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Ceophyslcal (Selsmlc) redlcuon Average acousuc veloclLy as a funcuon of depLh ls deLermlned (lnLerval LranslL ume (sec/)). 1he observed LranslL ume ls a poroslLy dependenL parameLer LhaL varles wlLh poroslLy accordlng Lhe relauonshlp: t = tmatrix1 ! " ( ) + tfluidRef: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 Lsumauon of lormauon ressure Whlle urllllng 8lL peneLrauon raLe usually changes slgnlcanLly wlLh formauon Lype. eneLrauon raLe logs can be used Lo ald ln a llLhology correlauon. eneLrauon raLe ln a glven Lype of formauon Lends Lo decrease wlLh depLh. When a Lransluon zone Lo a abnormal pressure zone ls encounLered, very oen a lower Lhan normal peneLrauon raLe ls observed. 1hls ls because Lransluon zones are frequenLly exLremely low permeable, hard, oen llmey formauon whlch acL llke a seal for Lhe hlgh pressure zone below. !usL above Lhe hlgh pressure zone buL sull wlLhln Lhe Lransluon zone, a reverse and lncrease ln peneLrauon raLe ls observed. 1hls ls because of a decrease of overbalanced pressure and a decrease of rock sLrengLh caused by under-compacuon. A loss of overbalanced decreases Lhe chlp hold down eecL". roblem: Many oLher varlables aecL peneLrauon raLe llke 8lL Lype, blL dlameLer, blL nozzle slze (consLanL) 8lL wear, blL balllng (vary) WC8, 8M, pump pressure, pump raLe (consLanL) Mud Lype (consLanL) Lecuve mud vlscoslLy, mud denslLy, sollds conLenL, slze dlsLrlbuuon ln mud (vary) Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 18 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Chlp Pold uown LecL 1he chlp hold down eecL Lends Lo keep Lhe cumngs on bouom of Lhe wellbore. Hydrostatic pressure of drilling fluid is higher than the formation pressure: the generated cuttings are cleaned from bottom by the impact force of the nozzles.As the formation pressure increases, cleaning is supported and the chip hold down effect decreases. Becausecuttings are more easy to be removed from bottom, the rate of penetration increases. Mud pressure Formation pressure Cuttings Cuttings d-LxponenL and Modled d-LxponenLln 1966 Lhe d-exponenL (ln d-unlLs) was lnLroduced (!orden and Shlrley, !1, nov. 66). lL normallse Lhe peneLrauon raLe 8C as a funcuon of WC8, 8M, and blL dlameLer. dexp=logROP ft / hr[ ]60 ! RPM min"1[ ]# $ % & ' ( log12 ! WOBlbf !1000[ ]1000 ! dbitin[ ]# $ % & ' ( -ln 1971(8ehm and McCledon, SL 3601) modled Lhe d-exponenL Lo accounL for Lhe amounL of overbalance: dmod = dexp!n!eWith !n is the equivalent mud density of the normal pore pressure, !e is the equivalent circulation density at the bit. Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 19 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben d-LxponenL and Modled d-LxponenLRef: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 ressure Calculauon uslng LheModled d-LxponenL-8ehm and McClendon gp = 7.65 ! log dmod( )n " dmod( )[ ]+ 16.5-Lmplrlcal relauon aer Zamora (CC!, uec 82) gp = gndmod( )ndmod( )Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 20 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben d-LxponenL and Modled d-LxponenL*A7)9'#L 1he modled d-exponenL daLa, shown ln Lhe 1able were compuLed from peneLrauon raLe daLa obLalned ln a shale formauon ln Lhe gulf coasL area. LsumaLe Lhe formauon pressure aL 13.000 uslng Lhe emplrlcal correlauon of 8ehm and McClendon. Solution: 1.Draw the plot 2.Calculate the slop of the normal pressure line (0.000038) 3.At a depth of 13.000 ft the values for dmod and (dmod)n can be read (1,64 and 1,17) 4.Calculate: gp = 7, 65 log (1, 64 !1,17) +16, 5 = 14 lb / galp = 0, 052 " 14 "13.000 = 9.464 psiRef: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 CLher MeLhods Lo 8ecognlze Abnormal lormauon ressureCumngs analysls: rock fragmenLs are analyzed and compared wlLh wells drllled ln Lhe same area. 1hls meLhod allows qulckly Lo ldenufy formauon LhaL are [usL above a hlgh pressure zone. MolsLure conLenL analysls of shale: shale cumngs are lnvesugaLed on Lhelr waLer conLenL. uurlng drylng Lhe sample, Lhe loss of pore waLer ls recorded. 1he shale poroslLy ls equal Lo Lhe volume of molsLure waLer dlvlded by Lhe bulk volume. Plgher Lhan normal poroslLy lndlcaLe abnormal pressure. Mud gas analysls wlLh real-ume esumauon of gas composluon clrculaLed ouL by drllllng mud. Ref: !""#$%& ()$##$*+ ,*+$*%%)$*+, lS8n 1-33363-001-4 21 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben 6%7D$(%# "%#//(%# 37/-+, :#;+, .#9$< Caslng Semng uepLh The knowledge of fracture resistance of rock during drilling is essentially to plan casing setting depth and to drill safe to final depth. The graph on the left shows an ideal form of casing setting depth determination. The equivalent pore pressure and the equivalent formation fracture pressure (but not the equivalent borehole collapse pressure) are plotted against TVD. Note that the arrows AB and CD represent the ideal mud weight to drill one section of the well without fracturing the formations and without gaining formation fluid influx. The consequence of this requirement is the definition of the casing points, or casing setting depths. 22 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben llndlng Lhe LlmlLs forlormauon 8reakdown Aer semng a caslng Lhe formauon below Lhe caslng shoe has Lo be LesLed for lLs breakdown properues (procedure see nexL sllde). As a resulL, Lhe fracLure pressure (bar) ls found.1hls fracLure pressure can be formulaLed as fracLure gradlenL (bar/m) or can be relaLed Lo a maxlmummud hydrosLauc welghL (equlvalenL frac mud welghL, equlvalenL frac denslLy). ln reallLy, Lhe equlvalenL clrculauon denslLy (LCu) should noL exceed Lhe equlvalenL frac mud welghL. Leak-C 1esL (LC1) 1.Drill out the casing shoe and sufficient new formation.2.Circulate the mud to ensure a consistent mud weight.3.Stop the rig pumps and shut the well in.4.Pump mud into the shut-in well at a very low rate. A typical pump rate of 0.25 to 0.5 barrels per minute (bpm) is used. A cementing unit is used so an accurate reading of volume and pressure can be obtained.5.Record the pressure and volume pumped. A graphical presentation should be made of these data to determine the point at which the fluid is being pumped into the formation (leak-off). A normal leak-off test will show the pressure increasing in a straight line with the volume of mud pumped. Once the fracture pressure is reached, the pressure will stop increasing with volume pumped as the fracture is being propagated. The pressure may actually decrease as fluid is pumped into the formation. Fig. 9 is an illustration of a graph obtained from a leak-off test.6.Once leak-off has been observed, stop pumping and observe the well. The pressure should remain relatively the same or decrease slightly once pumping has stopped. 7.Record the pressure where the fluid started leaking off into the formation. Convert this pressure to a mud weight equivalent by using the equation on the right:8.The fracture mud weight is calculated by adding the equivalent mud weight to the test mud weight.23 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben LC1 vs. ll1 A leak o LesL (LC1) ls usually referred Lo as a LesL where Lhe pressure ls ralsed unul a pressure leak. ln Lhls slLuauon Lhe formauon or shoe ls fracLured and pressure ls losL. roblem: Cnce Lhe formauon ls fracLured lL generally Lakes less pressure Lo open Lhe fracLures back up agaln.An exLended leak o LesL ls someume performed where Lhe fracLure closure pressure ls LesLed. 1he well ls pump up a second ume Lo see whaL Lhe new leak o pressure would be aer Lhe rsL LesL. A formauon lnLegrlLy LesL (ll1) ls a LesL where Lhe formauon ls pressured up Lo a predeLermlned polnL and Lhen bled down - wlLhouL Laklng Lhe formauon Lo fallure.Cenerally a ll1 ls performed raLher Lhan a LC1 so as Lo avold damage Lo shoe/formauon. LC1's are usually reserved for when lL ls absoluLely requlred Lo know how far one could go ln a cerLaln formauon wlLh Lhe undersLandlng LhaL Lhe slLuauon ls someumes worse aer Lhe LesL Lhan before.Mud WelghL Wlndow A hole secuon can conLaln shale/mudsLones LhaL may collapse lf lnsumclenL supporL by mud welghL ls provlded. 1o drlll Lhe secuon wlLh less or no lnsLablllLy problems Lhe max. mud welghL LoleraLed by sand/carbonaLes and Lhe mln. mud welghL Lo supporL Lhe mudsLone are requlred. 1hese bounds Lo Lhe mud welghL dene Lhe ,mud welghL wlndow. ln hlgh LecLonlcally sLressed reglons Lhe collapse gradlenL ln Lhe shale can exceed Lhe fracLure gradlenL ln Lhe sands, even for verucal wells. lncreased well lncllnauon reduces Lhe wldLh of Lhe mud welghL wlndow. 24 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Caslng Semng uepLh Theselectionofthenumberofcasingstringsandtheirsetting depthsgenerallyisbasedonaconsiderationoftheporepressure gradients and fracture gradients of the formations to be penetrated.Theporepressureandfracturepressureareexpressedasan equivalent density and are plotted vs. depth. A line representing the planned-mud-density program also is plotted. The mud densities are chosentoprovideanacceptabletripmarginabovetheanticipated formationporepressuretoallowforreductionsinmudweight causedbyupwardpipemovementduringtrippingoperation.A commonly used trip margin range is 0.2 - 0.5 ppg. 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 8,09,010,011,012,0 TVD (ft) EMW (ppg) SLep 1: lomng Lhe Mud WelghL Wlndow 23 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 8,09,010,011,012,0 TVD (ft) EMW (ppg) SLep 2: llndlng Lhe Secuons urllllng mud welghLs Caslng semng depLhs number of secuons Ref: .%/)0#%12 3%## 40*5/)1670*, lS8n 0-471-96938-9 SLep 3: Pole and Caslng ulameLer (1/2) 5 inch Production in a 6 ! inch hole 8 5/8 inch Intermediate 2 in a 10 5/8 inch hole in a 16 inch hole 11 3/4 inch Intermediate 2 18 5/8 inch Surface in a 24 inch hole 30 inch Conductor Standard Solution 26 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Ref: .%/)0#%12 3%## 40*5/)1670*, lS8n 0-471-96938-9 SLep 3: Pole and Caslng ulameLer (2/2) 5 inch Production in a 6 1/8 inch hole 7 inch Intermediate 2 in a 8 ! inch hole in a 10 5/8 inch hole 9 5/8 inch Intermediate 2 11 3/4 inch Surface in a 14 ! inch hole 16 inch Conductor Low Clearance Solution 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 8,09,010,011,012,0 TVD (ft) EMW (ppg) SLep 4: llnal 8esulLs Production Casing: 5 in. @ 10,000ft Intermediate 2: 8 5/8 in. @ 7,900ft Intermediate 1: 11 3/4 in. @ 4,500ft Surface Casing: 18 5/8 in. @ 1,000ft Standard Solution 27 PE DESIGN, PART A - DRILLING ENGINEERING:Formation Properties, Casing Setting Depth Chair of Drilling Engineering - University Leoben Caslng ueslgn- Caslng Semng uepLh and number of SLrlngs -8eslde Lhe conslderauon of formauon pore pressure and fracLure gradlenL, oLher facLors lnuence caslng semng depLh: -klck Scenarlos can be lncluded ln semng depLh esumauon.-8egulaLory requlremenLs may dlcLaLe Lhe proLecuon of underground sources of drlnk waLer or oLher zones Lo a speclc depLh. -Pole problems llke wellbore sLablllLy or dlerenual sucklng oen wlll need a cased borehole Lo conunue drllllng safely. -Zones may be lsolaLed when conLamlnauons or cross-ow ls noL deslred. -ln dlrecuonal drllllng lL ls of large lmporLance Lo avold key seaLs ln Lhe curved secuon of Lhe wellbore. A caslng provldes mechanlcal lnLegrlLy of Lhls poruon. -Lxplorauon wells oen need addluonal caslng sLrlngs Lo compensaLe Lhe uncerLalnLy ln pore pressure and fracLure gradlenL predlcuon. Ref: .%/)0#%12 3%## 40*5/)1670*, lS8n 0-471-96938-9