Reservoir Characterization of an Isolated Carbonate Buildup, Reinecke Field, West Texas

Arthur H. Saller¹, J. A. D. (Tony) Dickson², and Steve Robertson³, 
¹ Unocal Corporation, Sugar Land, Texas
² Cambridge University, Cambridge, England
³ Pure Resources, Midland, Texas

Reinecke Field in Borden County, Texas was characterized in preparation for a crestal CO₂ flood. Major parts of the project included (1) deepening and coring of many wells that initially only penetrated the uppermost part of the reservoir, (2) acquisition and interpretation of multiple 3D seismic surveys, (3) acquisition and interpretation of multiple VSP and cross well tomographic surveys, (4) construction of a geocellular reservoir model, (5) fluid flow simulation and history match of the reservoir from time of discovery (1950) to the present, and (6) use that model to predict CO₂ flood response and optimization of the CO₂ flood operation at Reinecke Field. A full field model which included all of the wells in the CO₂ flooded area and incorporated as much detail as possible of the reservoir and fluid properties was needed. 

Reinecke field is a carbonate buildup in the southern part of the Horseshoe Atoll. Since discovery in 1950, it has produced over 82 million barrels of oil. Four depositional sequences (60-80 ft thick) and nine depositional facies were identified in the Upper Pennsylvanian reservoir interval. The reservoir is ~70% limestone and 30% dolomite. Porosity is widespread in both lithologies. Most depositional facies have average porosities of 9-13% where still limestone. Important pore types in limestones include intercrystalline microporosity, molds, intergranular pores, fractures, and vugs. Limestones dominated by microporosity have low permeability, commonly 1-30 mD. Limestones with fractures and vuggy pores commonly have permeability greater than 100 mD. Lime mudstones are rare, but have distinctly lower porosity (average of 1.4%) and permeability (average of < 1 mD). Average limestone porosity is 11.2%, and average limestone permeability is 165 mD. In contrast, dolomite has generally lower porosity (average of 8.3%), but much higher permeability (average horizontal of 894 mD). Discontinuous shales comprise less than 1% of the gross reservoir. Discontinuous lime mudstones and shales in the lower part of sequences form low permeability baffles. Therefore, the south dome of Reinecke is characterized by relatively continuous vertical and horizontal porosity and permeability with high permeability streaks and discontinuous low permeability baffles. Excellent reservoir continuity and water injection into the underlying aquifer have allowed a good bottom water-drive and excellent primary and secondary recovery (55% of the original oil in place). Pore systems that are well connected throughout the reservoir have allowed a crestal CO₂ flood to be designed for Reinecke field. CO₂ is being injected into the top of the structure to mobilize residual oil and push an oil bank down through the reservoir to recover residual and bypassed mobile oil.