An accurate estimation and optimization of bottom hole back pressure in managed pressure drilling

Transcription

1 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p Egieerig, Eviromet A accurate estimatio a optimizatio of bottom hole back pressure i maage pressure rillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS * Departmet of Petroleum Egieerig, Uiversity of Port Harcourt, Nigeria. (s): aloriji000@yahoo.com; marcus.sikak@yahoo.com; * Nsikak Maurice Marcus, phoe: , Receive: November 4, 06 / Accepte: Jue 6, 07 / Publishe: Jue 30, 07 Abstract Maage Pressure Drillig (MPD) utilizes a metho of applyig back pressure to compesate for wellbore pressure losses urig rillig. Usig a sigle rheological (Aular Frictioal Pressure Losses, AFPL) moel to estimate the backpressure i MPD operatios for all sectios of the well may ot yiel the best result. Each sectio of the hole was therefore treate iepeetly i this stuy as ata from a case stuy well were use. As the backpressure is a fuctio of hyrostatic pressure, pore pressure a AFPL, three AFPL moels (Bigham plastic, Power law a Herschel Bulkley moels) were utilize i estimatig the backpressure. The estimate backpressure values were compare to the actual fiel backpressure values i orer to obtai the optimum backpressure at the various well epths. The backpressure values estimate by utilizig the power law AFPL moel gave the best result for the /4" hole sectio (average error % of.855%) while the back pressures estimate by utilizig the Herschel Bulkley AFPL moel gave the best result for the 8 /" hole sectio (average error % of.3%). The stuy showe that for hole sectios of turbulet aular flow, the power law AFPL moel fits best for estimatig the require backpressure while for hole sectios of lamiar aular flow, the Herschel Bulkley AFPL moel fits best for estimatig the require backpressure. Keywors Maage Pressure Drillig; Back Pressure; Aular Frictioal Pressure losses; Bigham Plastic moel; Power Law moel; Herschel Bulkley moel; Hyrostatic 39

2 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig pressure; Pore Pressure Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS Itrouctio The worl's populatio cotiues to grow at a geometric rate, which meas there will be a proportioate icrease i ema of eergy. For this reaso, egieers a scietists are i costat search of ewer sources of eergy a ew ways to completely exploit existig eergy sources. Toay, there is a costat eclie i crue reserves hece the ee to explore more challegig a complex eviromets. Drillig i these challegig eviromets usig the covetioal rillig metho coul easily lea to rillig hazars such as: Kick; lost circulatio; borehole istability a stuck pipe which are the major cotributors to No- Prouctive Time (NPT) []. Discoveries have show that NPT accout for approximately 0% of total rig time a ca be much higher i ifficult a complex terrais. Rig rates are o the high, with some rigs goig for as high as $M per ay, showig the strog impact of NPT o rillig cost. As the challege of a arrow rillig wiow becomes icreasigly proouce, rillig with the covetioal metho will lea to the settig of may casig strigs at relatively shallower epth as a result of tryig to avoi the obvious rillig problems. This also leas to a reuce prouctivity a a higher well cost. MPD is ow see as a techology that may provie a oteworthy icrease i cost-effective rill-ability by reucig excessive rillig relate costs typically relate to covetioal offshore rillig, kowig that about 70% of curret crue oil offshore reserves caot be rille ecoomically usig the covetioal metho of rillig []. MPD is very effective i reucig NPT that are rillig relate a also eable the rillig of prospects that techically a ecoomically are ot feasible to rill usig the ormal covetioal rillig metho. Accorig to the Iteratioal Associatio of Drillig Cotractors (IADC), Maage Pressure Drillig is a aaptive rillig process that is use to precisely cotrol the aular pressure profile throughout the wellbore [3]. MPD is therefore a avace form of well cotrol where a close a pressurize mu system is applie to eable a more precise cotrol of wellbore pressure profiles tha just mu hyrostatic a the pump pressure ajustmets [3]. The primary objective of MPD is to get the pressure limits of the ow hole a proportioally maage the hyraulic aular pressure profile. MPD may iclue cotrol of backpressure, flui esity, flui rheology, aular flui level, circulatig frictio, a hole geometry or combiatios thereof. MPD has bee prove to eable rillig of what might 40

3 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p otherwise be ecoomically u-rillable prospects a MPD is goo o its way to becomig the status quo techology over the ext ecae ue to the fact that it icreases recoverable assets [3]. The Costat Bottom Hole Pressure (CBHP) variatio of MPD is a techique associate with the cotrol of backpressure to attai the goal of a MPD operatio. The require back pressure term for MPD operatio is very importat to achieve a successful CBHP MPD operatio. Therefore, it is ecessary to have a very reliable tool for estimatig the require back pressure. Aother challege with the CBHP MPD operatio is that most of the methos use i the hyraulics calculatios i MPD operatios assume just oe rheological moel i all hole sectios, meawhile i reality, ifferet sectios of the hole may fit best to ifferet rheological moels. A simulate research was carrie out to etermie the best rheological moel i preictig pressure losses i rille wells [4]. The Bigham Plastic, Power law a Herschel Bulkley moels were all compare. The pressure losses gotte from these three moels were compare to the pressure losses gotte from fiel ata of wells rille with both water a oil base mu. It was fou that o oe moel was completely aequate, as rheological behaviour chage from oe hole sectio to aother. O the whole though, it was coclue that the Herschel Bulkley moel was best i preictig pressure losses i the pipe (96% accuracy) while the power law moel was best i preictig aular pressure losses (93%) [4]. Use of MPD techologies ca ifluece may wellbore pressure-relate rillig challeges, icluig lost circulatio, kicks, wellbore ballooig, tight pore pressure(pp)/fracture pressure (FP) margis, close tolerace casig programs, wellbore stability problems, shallow water/gas flows, slow ROP, etc [5]. These techologies may also eable future well programs that are curretly thought to be covetioally uesigable with sigle graiet mu systems [5]. Some experimetal aalysis were carrie out i [6] to ascertai the best flui rheology moel for HPHT coitio (40 to 800F a 500 to 000psi) usig u-weighte - paraffi base rillig flui (sythetic mu) i MPD operatios. A equatio to moel the effect of temperature a pressure o rillig flui esity was evelope. They compare the Bigham plastic, Power law a Yiel power law moels to their experimetal fiigs. The yiel power law gave the most accurate result whe compare to the experimetal result [6]. Hece the Yiel power law at the actual hole temperature a pressure was use as the yarstick to check for the accuracy i usig Bigham Plastic a Power law moels to estimate the pressure graiets with surface parameters usig ifferet flow rates. From the 4

4 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS stuy it was fou that the iscrepacies betwee pressure graiets gotte at actual well temperature a surface coitio icrease as the flow rate ecrease a it was coclue that the Bigham plastic moel with surface parameters woul estimate pressure graiets with the least error at low temperature coitios while the power law moel with high shear rate parameters woul estimate both pipe a auli pressure graiet with the highest accuracy [6]. I [7] it was state that rillig-grae barite limits rillig fluis esig for wells with critically arrow hyraulic operatig wiows. This limitatio ca be overcome by formulatig a Treate Microize Barite (TMB) istea of API barite, as TMB prouces a low rheology flui that may reuce the owhole frictioal pressure by 0.5ppg with miimal risk of barite sag or settlemet [7]. A ew approach to rillig flui esig that ucouple flui rheology from the risk of barite sag a settlemet was evelope. This was accomplishe by reucig the particle size of API barite from 97% less tha 75 micros to 97% less tha 5 micros, hece the rate of seimetatio i the rillig flui was sigificatly reuce [7]. A stuy to kow how pressure cotrol is affecte a sometimes limite by the actual available ata a its quality, equipmet, hyraulic moels, cotrol algorithm a ow hole coitio urig MPD operatios i ERD wells was carrie out i [8]. I plaig MPD i log wells, it is very vital to establish the limits o what ca be accurately a robustly achieve [8]. It was coclue that special care shoul be take whe applyig MPD i ERD wells because, ERD wells are more complex a challegig whe compare to shorter wells [8]. I [9] a careful stuy of the Herschel Buckley moel was carrie out a a ew moel was evelope by moifyig the Herschel Buckley moel. A explicit equatio betwee the wall shear stress a the volumetric flow rate for pipe a aular flow from Herschel Buckley flui moel was evelope [9]. A ew relatio for pipe a aular Reyols umber a frictioal pressure rop was establishe. The ew moel was valiate usig well ata from Sichua Basi a it was coclue that the ew moel preicte a calculate hyraulics more accurately tha the other traitioal moels previously use i MPD operatios [9]. Simulatio aalysis for kick etectio, cotrol a circulatio usig MPD were carrie out i [0]. The beefits of automate iflux etectio a cotrol usig MPD system compare to a covetioal well cotrol metho were highlighte. The simulatios successfully etecte a cotrolle a gas iflux i oil base mu while rillig i oshore wester Caaa. It was coclue that the curret MPD system has the potetial for rillig formatios with arrow pressure margis through their accuracy a precisio i 4

5 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p pressure cotrol a early kick etectio [0]. I [] a simple hyraulics moel calle the "fit-for purpose" hyraulics moel was evelope a it was use for computig the owhole pressures a to provie a choke pressure set poit for automate MPD systems. I [] a successful applicatio of MPD i a eep exploratio well offshore Egypt was escribe. It was coclue that utilizig the CBHP techique of MPD coul miimize the problems i the wells. The use of MPD is becomig more popular especially i offshore applicatio to mitigate rillig hazars a ehace prouctio rates which i tur maximizes profit. The mai aim of this stuy is to apply the cocepts of Costat Bottom Hole Pressure (CBHP) techique of MPD to evelop a computer moel (usig visual basic ot et) that ca estimate a optimize the backpressure require to mitigate rillig hazars urig MPD operatios. This stuy also aims to propose the best rheological (AFPL) moel that will give a perfect fit for the rillig hyraulics calculatio for CBHP MPD operatios for the various hole sectios of well. Material a Metho The importace of mitigatig rillig hazars caot be overemphasize. The problems of lost circulatio, borehole istability, kick a stuck pipe remais the major cause of NPT a shoul be properly maage a cotrolle. The ability to precisely cotrol the pressures i the wellbore will go a log way i helpig to miimize these problems. Data Collectio from the fiel The ata use for this stuy were obtaie from a fiel i West Africa a it iclue the pore pressure, fracture graiet, rheological properties of the flui use, hole size a epth, rill strig compoets, sizes a legths. The well comprise of three hole sectios. The 7 /" hole, /4" hole a the 8 /" hole sectios. The 7 /" hole sectio was rille usig the covetioal rillig techique. But the /4" a 8 /" hole sectios were rille usig Maage Pressure Drillig (MPD) techiques as show i tables 3 a 4 of the appeix. Aalysis Metho A software moel (Marc.soft) was evelope usig visual basic.net programmig 43

6 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS laguage, to estimate the backpressure from the pore pressure, hyrostatic pressure a maipulatio of the AFPL moels. The MarcSoft computer software is user friely a easy to maipulate. Data ca either be type irectly ito software or uploae from a excel file ito the software. The software also evaluate the percetage errors from usig each of the three state AFPL moels (Bigham plastic, power law a herschel bulkley) respectively for backpressure estimatio. This approach mae it easy to select the most accurate AFPL moel for MPD operatios i the various well sectios/epths as the estimate back pressure values were compare to the actual backpressure values from the fiel ata. For MPD operatios, the Bottom Hole Pressure (BHP) must be maitaie i betwee the Pore Pressure (PP) a Fracture Pressure (FP) for effective cotrol. I the CBHP metho of MPD, the BHP is a fuctio of the mu hyrostatic pressure (HP), the aular frictio pressure losses (AFPL) a the Back pressure (BP), Eq. (). BHP = HP + AFPL + BP () But, Eq. (): PP BHP FP () Combiig equatios a, Eq. (3): BP PP - (AFPL + HP) (3) Where: MW - mu weight, ppg; TVD - true vertical epth, ft. HP = 0.05 x MW x TVD; (4) Three AFPL moels (Bigham plastic, power law a Herschel bulkley) were utilize for this stuy so as obtai the best moel for optimal backpressure estimatio. Bigham Plastic moel The costitutive Bigham Plastic flui equatio is give as Eq. (5-7): (5) y p Where: τ - shear stress; τy - yiel poit (lb/00ft ); µp - plastic viscosity (cp); γ - shear rate (sec - ). μp = ϴ600 - ϴ300 (6) τy = ϴ300 - µp (7) Where: ϴ600 - ial reaig at 600 viscometer RPM, ϴ300 - ial reaig at 300 viscometer RPM 44

7 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p If flow is lamiar (eq. 8), pv y AFPL Where: µp - plastic viscosity (cp); v = average velocity (ft/sec); - hole or casig iameter (iches); - rill strig iameter (iches); τy - yiel poit (lb/00ft ); AFPL - aular frictioal pressure losses (psi). If flow is turbulet (Eq. 9): v a AFPL L Turbulet criteria, Eq. (0 a ): 5 y a p (0) v 757 N Re () a For Bigham plastic flui, flow is turbulet if NRe > 00 (Bourgoye et al 99) Where: NRe - Reyols umber; µa - apparet viscosity (cp); µp - plastic viscosity (cp); ρ - flui esity (ppg); L - legth/epth (ft); AFPL - aular frictioal pressure losses (psi); v - average velocity (ft/sec); - hole or casig iameter (iches); - rill strig iameter (iches); τy - yiel poit (lb/00ft ). (8) (9) Power law moel Power law moel is represete by Eq. (-7): τ = Kγ () Where: K = Cosistecy Iex, = flow behavior iex, γ = shear rate (sec - ), 00 a log (3) 3 K a 5. 3 a (4) 5. Where: ϴ00 - ial reaig at 00 viscometer RPM; ϴ3 - ial reaig at 3 viscometer RPM; Ka - cosistecy iex (i aulus); a = flow behavior iex (i aulus). AFPL fv. L (5) 45

8 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS N Re a 757v (6) Where: f - frictio factor; AFPL - aular frictioal pressure losses (psi); ρ - flui esity (ppg), L - legth/epth (ft); v - average velocity (ft/sec); - hole or casig iameter (iches); - rill strig iameter (iches); µa - apparet viscosity (cp). a a K a a a (7) a 44v If flow is lamiar, Eq. (8): 6 f N Re (8) If flow is turbulet, Eq. (9-): a f N b Re (9) Where: f - frictio factor; Ka - cosistecy iex (i aulus); a - flow behavior iex (i aulus), all other reoccurrig parameters remai the same. log 3.93 a a 50 (0).75 log a b 7 () Turbulece criteria: - If NRe is less tha , the flow is lamiar; - If NRe is greater tha , flow is turbulet; - But if NRe is betwee ( ) a ( ) flow is trasitioal a we have Eq. (): N Re a 4 N f Re b () Where: NRe,, a a f are the same as i preceig equatios. Herschel Bulkley moel The Herschel Bulkley moel is give by the equatios 3-8: y K (3) Where: K = cosistecy iex; - flow behavior iex; γ - shear rate (sec - ); τy - yiel poit 46

9 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p (lb/00ft ); τ = shear stress (psi). y y log 3 (4) y K (5) y Ca K v v N 4 Re (6) Where: ϴ600 - ial reaig at 600 viscometer RPM, ϴ300 - ial reaig at 300 viscometer RPM; NRe - Reyols umber; v - average velocity (ft/sec); ρ - flui esity (ppg); - hole or casig iameter (iches); - rill strig iameter (iches); τy - yiel poit (lb/00ft ); L - legth/epth (ft). y y a Q K C 4 (7) Where: K - cosistecy Iex, - flow behavior iex, - hole or casig iameter, (iches), - rill strig iameter (iches), τy - yiel poit (lb/00ft ), Q - pump rate (GPM). 3 l Q f AFPL (8) Where: f - frictio factor; AFPL - aular frictioal pressure losses (psi); ρ - flui esity (ppg); - hole or casig iameter (iches); - rill strig iameter (iches); L - legth/epth (ft); Q - pump rate (GPM). Turbulece criteria, Eq. 3-33: z y N cr Re 8 (9)

10 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS log 3.93 y (30) log z (3) 7 If NRe is less tha Nrecr, the flow is lamiar, If NRe is greater tha Nrecr, the flow is turbulet. If flow is lamiar, Eq. (3): f 8 N Re If flow is turbulet, Eq. (33): Z (3) f y C a NRe (33) Figure is a flow chat that was evelope to epict the moe of operatio of the Marc.Soft software applicatio for estimatio a optimizatio of backpressure for MPD operatios. The first thig to o after eterig the Marc.Soft eviromet is to iput ata. The ata ca be maually etere ito the software by selectig the 'sample ata' optio otherwise select the 'import ata' optio to irectly uploa the ata from a existig MS Excel file. The ext step is to select the Aular Frictioal Pressure Loss (AFPL) moels oe after the other util all three AFPL moels programme (Bigham plastic, Power law a Herschel Bulkley AFPL moels) have all bee selecte. The ext step is to select the evaluate back pressure optio to effect the estimatio of back pressure usig all three AFPL moels at oce. Next step is to valiate the back-pressure estimates from all three moels by cofirmig the percetage error estimates gotte from usig each of the three AFPL moels as compare to the actual fiel back pressure. Select the AFPL moel with the least error a the e. 48

11 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p Figure. Flow Chart for Back Pressure Estimatio from Marc.Soft (06) The followig assumptios were mae urig evelopig this optimizatio moel:. The rill strig is cocetrically place i the ope hole.. The ope hole sectios are circular i shape with kow iameters. 3. The rillig flui is icompressible. 49

12 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS 4 Temperature a pressure have opposig effects o the flui rheology, hece their overall effect o the rillig flui is eutral. Results a iscussio The summary of the results gotte from utilizig the three rheological moels are presete here. The focus was to get the AFPL moel that gave the best estimate of the back pressure to eable proper esig a a real-time aalysis for a MPD system. The well ata as show i tables 3 a 4 i the appeix were for the two ifferet hole sectios (.5" a 8.5''). MPD was use i this well because of the arrow rillig wiow betwee the pore pressure a the fracture graiet. The results were presete accorig to iiviual hole sectios. The well ata i the Appeix (table 3) were obtaie from a fiel i West Africa. Results for the /4" hole sectio The estimate Back pressure values from the ifferet AFPL moels for this hole sectio are show below i table (table is a extract from the evelope software). Table - The estimate back pressures from usig each of the three AFPL moels a their respective error % estimate (3930 to 8300 ft) Depth Fiel Back Bigham Power Herschel Error % Error % Error % from Pressure, Plastic, law BP* Bulkley from from power Herschel Psi BP* (psi) (psi) BP* (psi) Bigham Plastic BP* law BP* Bulkley BP*

13 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p BP*: Back Pressure Results for the 8 /" hole sectio The estimate Back pressure values from the ifferet AFPL moels for this hole sectio are show below i table (table is a extract from the evelope software). Table - The estimate back pressures from usig each of the three AFPL moels a their respective error % estimate (8300 to 3500 ft) Depth Fiel back pressure (psi) Bigham plastic, BP* (psi) Power law BP* (psi) Herschel Bulkley BP* (psi) Error % from Bigham Plastic BP* Error % from power law BP* Error % from Herschel Bulkley BP*

14 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS BP*: Back Pressure 5

15 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p Results for the /4" hole sectio The /4" well sectio was from 3930 ft to 8300 ft. The rill strig use for this sectio comprise of rill pipes from 3930 ft to 700 ft with a outer iameter of 6.65" a iteral iameter of 5.98", Heavy Weight Drill Pipes (HWDP) from 700 ft to 7700 ft with a outer iameter of 6.65" a iteral iameter of 4.5", Drill Collars (DC) from 7700 ft to about 8000 ft with a outer iameter of 9.5" a iteral iameter of 3.00", Jars from 8000 ft to 8060 ft with a outer iameter of 7" a iteral iameter of.75", MWD tool from 8060 ft to 840 ft with a outer iameter of 6.750" a iteral iameter of 3.00", a fially the Mu-Motor with outer iameter of 8.5" a iteral iameter of.00" combie with some other BHA ra from 840 ft to the e of the hole sectio. MPD was use i this hole sectio. There was a of trasitio from lamiar to turbulet flow regime ue to a tight ope hole - rill strig aulus accompaie by a high pump rate. From table it was observe that the back pressures estimate whe usig the Bigham plastic moel AFPL gave a egative average error percet (-3.59%) whe compare to the actual back pressures. The back pressures estimate whe usig the power law moel AFPL, gave a average error percet of.855% i compariso to the actual back pressure. This shows goo accuracy a therefore coul be successfully use to moel the require backpressure for ay hole sectio havig a similar cofiguratio a pump rates for the CBHP techique of MPD operatio. The back pressures estimate by utilizig the Herschel Buckley moel AFPL, gave a average error percet of -5.4% i compariso to the actual back pressure. The back pressures estimate whe usig the power law moel AFPL gave the best estimatio of backpressure for this hole sectio. Results for the 8 /" hole sectio The 8 /" sectio ra from 8300 ft to 3500 ft. The rill strig use for this sectio comprises of rill pipes from 8300 ft to 300 ft with a outer iameter of 5" a iteral iameter of 4.76", Heavy Weight Drill Pipes (HWDP) from 300 ft to 800 ft with a outer iameter of 5" a iteral iameter of 3", Drill Collars (DC) from 800 ft to about 300 ft with a outer iameter of 6.5" a iteral iameter of.8", Jars from 300 ft to 380 ft with a outer iameter of 6.5" a iteral iameter of.75", MWD tool from 380 ft to 3400 ft with a outer iameter of 6.750" a iteral iameter of 3.00", a fially the Mu-Motor with a outer iameter of 6.5" a iteral iameter of.00" combie with some other BHA ra from 3400 ft to the e of the hole sectio. The flow regime was fully 53

16 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS turbulet from epth 8300 ft to 800 ft. From epth 900 ft to 3500 ft, the flow regime switche agai to lamiar largely ue to the rop i pump rates. From table the backpressures estimate by usig the Bigham plastic moel AFPL gave a average error percet of -8.88% for the whole 8 /" sectio. From 8300ft to 800ft, the backpressures estimate by usig the power law moel AFPL gave a average error percet of.77% i compariso to the actual back pressure. From 900 ft to 3500 ft, the back pressures estimate by usig the power law moel AFPL gave a average error percet of 35.9%. It ca be clearly see that from 8300 ft to 800 ft where the pump rate was high a the flow turbulet, the back pressures estimate by usig the power law moel AFPL showe goo accuracy, but from 900 ft to 3500 ft where the pump rate roppe heavily a flow switche to lamiar, the back pressures estimate by usig the power law moel AFPL performe poorly. This wie variatio may be ue to the fact that the power law moel fails to accout for ay form of yiel stress. From 8300ft to 800ft, the back pressures estimate by usig the Herschel Buckley moel AFPL gave a average error percet of -4.08% i compariso to the actual back pressure. From 900 ft to 3500 ft, the back pressures estimate by usig the Herschel Bulkley moel AFPL gave a average error percet of.3%. It ca be clearly see that from 8300 ft to 800 ft where the pump rate was high a the flow turbulet, the back pressures estimate by usig the Herschel Bulkley moel AFPL were a bit uerestimate. But from 900 ft to 3500 ft where the pump rate roppe heavily a flow switche to lamiar, the back pressures estimate whe usig the Herschel Bulkley moel AFPL performe best. O the average for this whole sectio, the Herschel Bulkley moel AFPL gave the best estimatio of the back pressure. Coclusios Base o the results from the stuy it was coclue that, whe moelig a well (rillig hyraulics moelig) for MPD operatios i hole sectios where turbulet aular flow is preomiatly expecte, the power law AFPL moel fits best for estimatig the require backpressure while for hole sectios where lamiar aular flow is preomiatly expecte, the Herschel Bulkley AFPL moel fits best for estimatig the require backpressure. 54

17 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p The tool/software evelope i this stuy usig visual basic.et programmig laguage for estimatig the require backpressure is very reliable a efficiet for moelig CBHP MPD operatio for wells arou West Africa. Depth, ft Desity, ppg Appeix Table 3 - Drillig ata from a Well X i West Africa V, ft/s hole size, ich O.D, iches PV, Cp YP, lb/00ft Q, gpm HP, Psi PP, Psi Back Pressure, psi

18 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS Table 4 - Aitioal flui ata Powel law Powel law Herschel Buckley Herschel Buckley (a) (Ka) (a) (Ka)

19 Leoaro Electroic Joural of Practices a Techologies ISSN Issue 30, Jauary-Jue 07 p Refereces. Haega D., Drill thru the limits-cocept a eablig tools, presete at the SPE/IADC Maage Pressure Drillig a Uerbalace operatios coferece a exhibitio, Kuala Lumpur, Malaysia, 4 to 5 February 00.. Aeru S.A., Aewale D., Chimaroke A., Ekeie E., a Oagme B., Optimizig the Drillig HPHT/Deep offshore wells usig maage pressure rillig techiques, presete at the SPE Nigeria Aual Iteratioal Coferece a Exhibitio hel i Lagos, Nigeria, 5-7 August Haega D., Case stuies Offshore maage pressure rillig, presete at the SPE Aual Techical Coferece a Exhibitio hel i Sa Atoio, Texas, U.S.A., SPE 0855, 4 7 September Ayei K., Osisaya S.O., Evaluatio of commoly use flui rheological moels usig evelope rillig hyraulic simulator, presete at the Petroleum Society's 5th Caaia Iteratioal Petroleum Coferece, Calgary, Alberta, Caaa, Jue 8-0, Braiar R.R., A process use i evaluatio of maage pressure rillig caiates a probabilistic cost-beefit aalysis, presete at the Offshore Techology Coferece hel i Housto, Texas, U.S.A., 8375, - 4 May Demiral B., Cuha J.C., New improvemets o maage pressure rillig, presete at the Petroleum Society's 8th Caaia Iteratioal Petroleum Coferece, Calgary, Alberta, Caaa, Jue -4, Doug O., Lee C., Drillig flui esig elarges the hyraulic operatig wiows of maage pressure rillig operatios, presete at the SPE/IADC Drillig Coferece a Exhibitio hel i Amsteram, the Netherlas, -3 March 0. SPE/IADC Ja E., a Hary S., Back pressure MPD i extee reach wells-limitig factors for the ability to achieve accurate pressure cotrol, presete at the SPE Berge oe ay Semiar Hel i Grieghalle, Berge, Norway, April 04. SPE 69 MS. 9. Fa H., Wag G., Peg Q., Wag Y., Utility hyraulic calculatio moel of Herschel Bulkey rheology moel for MPD hyraulics, presete at the SPE Asia Pacific Oil & 57

20 A Accurate Estimatio a Optimizatio of Bottom Hole Back Pressure i Maage Pressure Drillig Boiface Aleruchi ORIJI, Nsikak Maurice MARCUS Gas Coferece a Exhibitio hel i Aelaie, Australia, 4-6 October 04. SPE 7443 MS 0. Kiik K., Gumus F. a Osayae N., Automate yamic well cotrol with maagepressure rillig: A case stuy a simulatio aalysis, presete at the SPE/IADC Maage Pressure Drillig & Uerbalace Operatios Coferece & Exhibitio, Mari, Spai, 05.. Gle-Ole K., Oyvi, N.S., Lars I., a Ole M.A., Simplifie hyraulics moel use for a maage pressure rillig cotrol system, presete at the SPE/IADC Maage Pressure Drillig a Uerbalace operatios coferece a exhibitio, Dever, Colorao, U.S.A., 0, SPE Kerche F., Haega C., Pea a Armoe M., Maage pressure rillig eables rillig beyo the covetioal limit o a HPHT eep water well i the Meiterraea Sea, presete at the IADC/SPE Maage Pressure Drillig a Uerbalace operatios coferece a exhibitio hel i Dever, Colorao, U.S.A., 5-6 April 0. IADC/SPE