Improved Reservoir CharacterizationA Key to Future Reservoir Management for the West Seminole San Andres Unit

Abstract

A comprehensive reservoir study using a black-oil simulation model showedthat control of vertical movement of oil into the gas cap under waterfloodoperations was the key to maximizing oil recovery from this west TexasSan Andres reservoir. Recovery of an additional 4 MMSTB of oil isexpected as a result of a reservoir management plan which includes a46-well infill drilling program. Introduction Improved reservoir description is becomingrecognized as an essential requirement for effectivereservoir management. This is particularly important for the extremely heterogeneous, geologicallycomplex San Andres carbonate reservoirs of westTexas. The West Seminole field in west centralGaines County, TX, (Fig. 1) produces from the SanAndres formation at an average depth ofapproximately 5,100 ft. Fig. 2a shows the generalstructural configuration of the reservoir; it consistsof a large main dome with a smaller dome structureto the east. A large primary gas cap, shownschematically in Fig. 2b, covers most of the fieldarea. A summary of basic reservoir and fluid data ispresented in Table 1. Throughout the field's producing life, there hasbeen a question about the extent of verticalcommunication within the reservoir, particularly betweenthe oil zone and the overlying gas cap. This questionbecame a critical operating consideration when apattern waterflood was proposed in the early 1970's.An extensive reservoir study was undertaken topredict the future production performance of thefield under waterflood operations. The overall objective of this study was to developthe most profitable and effective reservoir managementprogram for the West Seminole San Andres Unit. Thefollowing specific objectives and procedures weredeveloped for the work.Use all available geologic and engineering datato develop a detailed and accurate reservoirdescription for this field.Incorporate the reservoir descriptioninformation into a black-oil computer simulationmodel. Use the simulator to verify and further refine the reservoir description by history matching thepressure and production data.Use the history-matched simulation model toproject future reservoir performance under currentwaterflood operations.Evaluate various alternative operating plans andrecommend the most effective reservoir managementprogram for the unit. JPT P. 2009＾