Innovative Reservoir Management - Key to Highly Successful Jay/LEC Waterflood

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Summary: A comprehensive surveillance program and detailed reservoir description data were combined to provide innovative reservoir management for the Jay/Little Escambia Creek (LEC) waterflood. As a result of effective management, this waterflood has proved highly successful. Benefits of surveillance and data gathering have outweighed costs greatly. Introduction: Following discovery of the Jay/LEC field Smackover reservoir in June 1970, an early decision was made by field operators to obtain extensive reservoir description data during field development. Consequently, 102 development wells were cored conventionally from 1970 to 1974. This resulted in the procurement of a wealth of reservoir rock data available for use in describing the reservoir to provide a basis for unitization and to plan and justify a waterflood project.1 During 1973, as planning for waterflood operations progressed, it became apparent that comprehensive surveillance was needed to complement the reservoir description data fully and, thereby, optimize recovery through effective reservoir management. A surveillance program was developed to monitor and control waterflood conformance in the thick-layered reservoir. Cased-hole logging tools along with pressure buildup and production tests are used extensively, in conjunction with permeability data from core analyses, to provide vertical conformance data. Areal conformance surveillance techniques employ radioactive tracers, reservoir pressure data, and interference tests. Use of surveillance information together with the reservoir description data yielded many new insights into water movement and zone depletion. Fluid movement analysis technique were developed, and several methods to improve recovery were defined. These include drilling, workovers, facility modifications, and injection balancing. These efforts have been responsible for maintaining field producing capability and delaying production decline until late 1979 and 75% of the estimated ultimate recoverable reserve had been produced. Field History: The discovery well for the field, St. Regis No. 1, was completed in the Smackover formation in June 1970. A total of 102 wells was drilled on 160-acre (65-ha) well spacing during the development period from 1970 to 1974. Eighty-nine wells were producers, and 13 were dry holes. The Jay/LEC field was unitized on March 1, 1974, to implement a waterflood, and a 3:1 staggered line drive pattern was selected.2 Ultimate recovery expected is 346 million STB (55×106 stock-tank m3) or 47.5% of the 728 million STB (116×106 stock-tank m3) of original oil in place. This represents 222 million STB (35×106 stock-tank m3) more recovery than from primary operations. Water injection began on March 5, 1974. The basic operating plan was to open the entire productive section in both injection and production wellbores and, thereby, waterflood all Smackover zones simultaneously. Injection wells were acid fractured using large staged treatments to create connecting vertical fracture systems between spaced sets of perforations. In production wells, the entire productive section was opened without acid fracturing to maintain the flexibility to control future water production. The 3:1 line drive pattern has operated very successfully. The rapid reservoir pressure decline experienced during primary operations was arrested quickly, and maximum oil allowable rates were sustained.3

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