OIL PRODUCTION ENHANCEMENT USING BOTTOM-HOLE WATER SINK: A GUIDELINE FOR OPTIMUM DESIGN APPLICATION

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1 IATMI 2006-TS-27 PROSIDING, Simosium Nasional & Kongres IX Ikatan Ali Teknik Perminyakan Indonesia (IATMI) 2006 Hotel Te Ritz Carlton Jakarta, Noember 2006 OIL PRODUCTION ENHANCEMENT USING BOTTOM-HOLE WATER SINK: A GUIDELINE FOR OPTIMUM DESIGN APPLICATION Taufan Maraendrajana; Institut Teknologi Bandung, and Iso Alliya; Institut Teknologi Bandung ABSTRACT Bottom ole water sink as been reorted to be a successful tool to increase oil roduction by minimizing water coning roblem. Te idea of tis metod is to create a ressure-sink in te water-zone to roide a counter force balance oosing te one caused by roduction troug te well erforation in te oil zone. Tis is done by same well roducing te water zone simultaneously wit te oil zone. Ten, wit aroriate design, it is exected te oil-water contact stay stable and te water coning is reented. Altoug some alications ae been successful, oters reorted failures wen imlementing tis metod. Te oosing results may be exlained by our conclusion of literature study tat tere is a missing link between te concet and te alication in te field. Tis work fills te missing link by deeloing a general guideline for otimum design of bottom-ole water sink. Te guideline considers interal erforation and reseroir anisotroy. Te imortant results are (i) otimum oil-water zone roduction ratio, (ii) generalized inflow erformance window (IPW) tat roide enelo for water coning, reerse coning and segregated flow, and (iii) critical rate for water coning. INTRODUCTION Water coning is a major factor tat reduces oil roductiity and oil recoery. Some researces conducted study on te critical rates 1-5 and water breaktroug time 6-7 as arameter considerations to control water coning. In some cases, roducing oil well below te critical rate is not considered economical. Downole (or bottom-ole) water sink (DWS) was introduced to control water coning witout limiting te oil roduction rate below its critical rate (Fig. 1). Te first attemt to use DWS concet is suggested by Driscoll 9 wit erforating te water zone to control water coning in addition to te erforation interals in te oil zone. Tis is a modification of te earlier atented metod by Widmyer 10 wo roosed a well comletion rincile wit searated roduction of oil and water by erforating bot te to and bottom comletion in te oil zone. Teoretical work on DWS was conducted by Wojtanowics et al Tese works studied te mecanism and erformance of DWS. Figure. 1. Scematic of downole water sink. 8 To differentiate from te ast researces, tis aer is intended to roide a unified graical aroac. It can be used by ractical engineers as a simle guideline for DWS design. Tis metod incororates arameters affecting water coning suc as ermeability anisotroy, and erforation interal. MODEL DESCRIPTION Results are generated using numerical reseroir simulator. As tis is a single well roblem, radial coordinate is best to reresent flow direction from reseroir into te well. Smaller grid block size is used near te well since fluid elocity increases near te well. Vertically, te model is diided into small tickness of layer to aroriately cature te water coning.

2 Te indicator used to ealuate te erformance of DWS is oil recoery factor at ten years of well life. Altoug one may ae different argument on te time san selection, it is more reasonable tan using ultimate recoery factor. Te reliminary analysis indicates tat te maximum oil recoery using DWS is acieed if erforated zone water is closed to te water-oil contact and te oil zone is erforated at te to. Tis is clearly exlained as follows; (i) erforating oil zone at te to will delay coning breaktroug, (ii) draining water closer to WOC requires less drawdown to balance water coning induced by te oil zone roduction. In te ealuation of DWS erformance, we use base case data resented by Inikori (2002) 13 as in Tables 1 and 2. Some well/reseroir and DWS design arameters are aried and te otimum condition is determined for eery set of arameter combination. Data range of te arameters mentioned aboe is listed in Table 3. of tis study, we are currently inestigating te effect of water-oil mobility). RESULTS AND DISCUSSION Te erformance of DWS comared to conentional well is deicted by Fig. 2. Addition DWS (if designed aroriately) in water zone increases oil recoery u to about 50% (equialent to incremental recoery of 43%). For tis case, te oil zone roduction is 100 stb/d and te water zone roduction is stb/d. Producing liquid of stb/d may be imossible from a single well. If we use ractical range, te reasonable alue is u to 5000 stb/d roduction from water zone. Tis constraint still gies us oil recoery factor of 30% (incremental recoery of 23%). Table 1. Rock Proerties Rock Caracteristics Oil Zone Water Zone Porosity, % Vertical ermeability, md Horizontal ermeability, md Comressibility, si-1 4x10-6 4x10-6 Table 2. Fluid Proerties Oil Bubble oint ressure, sia 1000 Comressibility, si-1 1.5x10-5 Density, lbm/cuft 53.9 FVF, rb/stb 1.26 Viscosity, c 1.25 Formation Water Comressibility, si-1 3x10-5 Density, lbm/cuft FVF, rb/stb 1.02 Viscosity, c 0.46 Table 3. Data Range Used in Simulation Model Variables Minimum Maximum Vertical anisotroy (k /k ), md Liquid roduction in te oil zone, stb/d Liquid roduction in te water zone, stb/d Standoff (from to) Perforation interal ( / o ) Tis aer does not ary water-oil mobility ratio, altoug tis ariable affect water coning. It is our first attemt to find weter te graical aroac is ossible for DWS design (oweer, as continuation Figure. 2. Performance of DWS. It is noted from Fig. 2 tat for a articular oil zone roduction rate, tere is an otimum liquid roduction from water zone for a DWS comletion. Oil recoery factor generally increases as te water zone roduction increases. Tis is because DWS reent water coning, and at some oint oil coning occurs in te water zone erforation. Te recoery factor sown in Fig. 2 is total oil recoery from bot to (oil zone) and bottom (water zone) comletions. Te total recoery decreases as te water zone roduction increases, after it as reaced a maximum recoery. During tis region, te oil coning extremely dominates as te reersal of water coning. For a gien reseroir and fluid caracteristics, te otimum DWS condition is determined from simulation. In case of enetration ratio (interal erforation) of 0.2, it is lotted in Fig. 3 for arious ertical anisotroy k /k. Linear relationsi between ratio of oil-water zone roduction and oil zone roduction is obsered for k /k from 0.1 to 1.

3 Inikori et al. 13,14 uses Inflow Performance Window (IPW) lot to identify flow regime during DWS oeration (Fig. 5). IPW correlate water zone roduction (q bottom ) and oil zone roduction (q to ) in term of Water Breaktroug Line (WBL) and Oil Breaktroug Line (OBL). Region below WBL indicates water coning and aboe OBL indicates reerse coning. Between te two lines, lower ortion is a region were segregated flow reails; te uer ortion is unstable contact water coning and reerse coning may occur alternately. Figure. 3. Otimum DWS for / o = 0.2. Fig. 3 sows different linear relationsi for different alue of k /k. Different / o also gies oter linear trends. It can be generalized using correlation in Eq. 1 to 3. Tis correlation is alidated by te simulation outut, and it is reasonably accurate (Fig. 4). R Were = Aq B (1) ot to k A (2) = k k.0048 B = (3) k o o Figure. 5. Examle of Inflow Performance Window. Because different combination of rock/fluid caracteristics and well enetration/standoff roduces different set of IPW, it is elful for ractical engineers to ae a single IPW lot wic unifies all different sets of IPW. Tis is roided tis study as exibited in Fig. 6. Figure. 4. Validation of Eq. 1. Otimum condition suc as resented by Eq. 1 to 3 does not differentiate between stable (segregated) or reerse coning flow. In some cases, te roduction from bottom comletion is re-injected into te reseroir. For tis scenario, one reents roducing oil from bottom comletion. In oter words, segregated flow sould reail and reerse coning flow is aoided. Figure. 6. Unified Inflow Performance Window. Te IPW sow in Fig. 6 is obtained from arious alues of ertical ermeability anisotroy, enetration ration, erforation standoff, and liquid rate of to and bottom comletions. Wit tis figure one can easily uses tose data information to get desired DWS roduction mode (i.e., reerse coning

4 or segregated flow). Te definition of Q to and Q bottom used in tis lot is as follows. α1 ( 10 ) k k α 2 α 3 Q to = Qto + (4) o β 2 β 3 β1 k Q = + ( 10 ) bottom Qbottom (5) k o Were: α1= , α2= , α3= ; and β1= , β2= , β3= ). Furter, combination of otimum DWS condition (Eq. 1) and IPW lot yields a DWS Guideline Plot (DGP) wic is sown in Fig. 7. Tis lot uses semilog axes. Te otimum line is generated for k/k = 0.5 and /o = 0.2. Maximum recoery for DWS is acieed generally in reerse coning mode. Tis cart can be interreted as aboe otimum line DWS is oer-designed and below water-breaktroug line DWS is under-designed. Te wite-color region is te eneloe for desired DWS condition (DWS Eneloe). CONCLUSIONS From tis study we obsere tat: 1. Te maximum total oil recoery for DWS well is generally obtained under reerse coning mode. 2. Correlation relating te reseroir/well roerties wit otimum DWS design is roosed. Te otimum condition is based on total oil recoery (to and bottom comletions). 3. DWS Guideline Plot (DGP) is roosed as a tool to ealuate and design DWS comletion. 4. For generalizing te alicability of DGP, inclusion of water-oil mobility ration sould be studied furter. Figure. 7. DWS Guideline Plot. Figure 8 sows alication of DWS Guideline Plot. Six field case istories are reiewed using tis lot. Te field data are taken from literatures. 11,15 Excet field A, te design for all fields are in te DWS Eneloe. For field A, te simulation sowed tat te original DWS design roduced water cone eigt aboe water table. Tis is consistent wit DGP lot as te DWS erformance for tis field lies in te water-coning mode or under-design (symbol labeled A). We found tat DWS erformance can be imroed if we increase water roduction from te bottom comletion (symbol labeled A ). ACKNOWLEDGEMENT Tis work is artially from Master Tesis of Iso Alliya at Institut Teknologi Bandung (ITB). We also tank to CMG (Comuter Modeling Grou) tat roides ITB wit educational license of reseroir simulator used in tis study. REFERENCES 1. Muskat, M. and Wyckoff, R.D.: An Aroximate Teory of Water Coning in Oil Production, Transactions AIME, 114, (1935), Meyer, H.I. and Gardner, A.O.: Mecanics of Two Immiscible Fluids in Porous Media, Journal Alied Pysics, 25, No. 11, (No., 1954), Weatly, M.J.: An Aroximate Teory of Oil/Water Coning, SPE 14210, Proceeding of Te SPE Annual Tecnical Conference and Exibition, Las Vegas, NV, Se , Caeron, I.: Teoretical Study of Coning Toward Horizontal and Vertical Wells in Anisotroic Formations: Subcritical and Critical Rates, SPE 15377, Proceeding of Te SPE

5 Annual Conference and Exibition, New Orleans, Oct. 5-8, Hoyland, L.A., Paatzacos, P. and Skjaeeland, S.M.: Critical Rate for Water Coning: Correlation and Analytical Solution, SPE Reseroir Engineering, (No., 1989), Sobocinski, D.P. and Cornelius A.J.: A Correlation for Predicting Water Coning Time, JPT, (May, 1965), Bournazel, C. and Jeanson, B.: Fast Water- Coning Ealuation Metod, SPE 3628, Proceeding of Te SPE Annual Conference and Exibition, New Orleans, LA, Oct. 3-6, Bowlin, K.R., Cea, K.R., Weeler, S.S. and Waldo, L.A.: Field Alication of In-Situ Graity Segregation to Remediate Prior Water Coning, SPE 38296, Proceeding of Te SPE Western Regional Meeting, Long Beac, CA, June 26-27, Driscoll, V.J.: Multile Producing Interals to Suress Coning, US Patent No. 3,637,731, Feb.1, Widmyer, R.H.: Producing Petroleum from Underground Formations, US Patent No. 2,855,047, Oct.3, Wojtanowicz, A.K., Xu, H. and Bassiouni, Z.: Oilwell Coning Control Using Dual Comletion Wit Tailie Water Sink, SPE 21654, Proceeding of Te SPE Production Symosium, Oklaoma City, Oklaoma, Aril 7-9, Sirman, E.I. and Wojtanowicz, A.K.: Water Cone Histerisis and Reersal for Well Comletions Using te Moing Serical Sink Metod, SPE 37467, Proceeding of Te SPE Production Symosium, Oklaoma City, Oklaoma, Marc 9-11, Inikori, S.O.: Numerical Study of Water Coning Control wit Downole Water Sink (DWS) in Vertical and Horizontal Wells, PD Dissertation, Louisiana State Uniersity and A&M College, Baton Rouge, LA, Inikori, S.O., Wojtanowics, A.K. and Siddiqi, S.S.: Water Control in Oil Wells Wit Downole Oil-Free Water Drainage and Disosal, SPE 77559, Proceeding of te SPE Annual Tecnical Conference and Exibition, San Antonio, TX, 29 Setember-2 October Sirman, E.I. and Wojtanowics, A.K.: More Oil wit Less Water Using Downole Water Sink Tecnology: A Feasibility Study, SPE 49052, Proceeding of te SPE Annual Tecnical Conference and Exibition, New Orleans, LA, October 1998.