Reservoir Management Practices

Summary This paper describes the reservoir management practices used at fieldsdeveloped and operated by Esso Production Malaysia Inc. (EPMI). The goal of EPMI's reservoir management activities is to maximize profitability andeconomical recovery of oil. Excellence in reservoir management is achieved withclearly defined and endorsed plans for management of each reservoir and acoordinated process to collect, analyze, validate, and integrate reservoirdescription and performance data into optimal development and depletion plans. Use of a multidisciplinary team to identify problems and to implement timely, innovative solutions is a key problems and to implement timely, innovativesolutions is a key ingredient. Through regular reports to management andfrequent discussions among functional groups, reservoir management objectivesand stewardship performance are communicated. Introduction Reservoir management is a significant component of EPMI's developmentplanning and production operations. Reservoir management planning, which beginsduring predevelopment phases, is emphasized throughout the productive lives ofthe reservoir and field to maximize profitability and economical oil recovery. As contractor to Petroleum Nasional Bhd. (PETRONAS), the Malaysian national oilcompany, EPMI currently operates 12 oil fields with 66 active reservoirs in the South China Sea. The fields are located within the 1976 production sharingcontract (PSC) areas (Fig. 1) about 130 to 260 km [80 to 160 miles] offshore Peninsular Malaysia. Production was initiated in 1978. By the end Peninsular Malaysia. Production was initiated in 1978. By the end of 1991, 28 platformshad been installed and developed with 755 completions. Five additionalplatforms are planned to complete development of the Seligi, Guntong, Tabu, and Dulang fields. The reservoirs in all fields except Seligi, Guntong, Tabu, and Dulang are mature, having produced more than 50% of their expected ultimaterecovery. Reservoir Types and Drive Mechanisms The major reservoirs operated by EPMI can be grouped into six types (see Fig. 2). Most major reservoirs have large associated gas caps where producedgas is reinjected for gas-cap expansion to displace oil downdip to productionwells, thereby avoiding oil losses to the gas cap. The major Groups E, J, and Ksandstones of the Bekok, Pulai, Tiong, Kepong, Semangkok, and Seligi fieldshave rim or pancake-type oil columns with large overlying gas caps and moderateto strong aquifer support. The Palas Group I sandstone is similar except thatthe aquifer support is weak because of poor rock quality and continuity in thesurrounding aquifer areas. At Irong Barat, gravity drainage with gas injectionfor pressure maintenance is the predominant drive mechanism because of the highdip angle, low solution GOR, and high permeability. Full voidage replacement bycrestal gas injection is required to avoid gas-cap shrinkage. The lower Group Jsandstone at Tinggi has strong aquifer support and no gas cap, so injection isnot required. The upper Group J sandstone, however, which is in communicationwith the lower group J sandstone, has a gas ca but weak aquifer support. Consequently, gas is reinjected. At the Tapis, Guntong, and Tabu fields, the Group I and J sandstones have weak aquifer support and long oil columns, soboth water and gas are injected to maximize recovery. Reservoir Management Goal and Key Objectives The company's reservoir management program is an ongoing, dynamic process ofcollecting, analyzing, validating, and integrating process of collecting, analyzing, validating, and integrating reservoir description data andperformance data into an optimal reservoir development and depletion plan. Thegoal of reservoir management is to maximize profitability and economicalrecovery of hydrocarbons. To achieve that goal, the following three keyobjectives were established.Mitigation of production decline in existingfields. With the mature fields exhibiting a decline in productive capacity ofmore than 15%/yr, capacity enhancement is a key requirement. Several programsimplemented to mitigate decline are discussed later.Aggressive pursuit ofnew field development. The recent work completed to confirm and implementdevelopment plans for the North Seligi resource potential illustrates theapproach used.Effective exploration and exploitation of new acreage. Withthe current exploration activities in the PM-5 and PM-8 PSC areas, new acreageis being exploited effectively, but these activities are not discussed in thispaper. Reservoir Management Process Reservoir management practices are initiated before development work beginsand continue throughout the life of the reservoir through the process shownschematically in Fig. 3. JPT P. 1296