Three-Dimensional Seismic Imaging and Reservoir Modeling of an Upper Paleozoic Reefal Buildup, Reinecke Field, West Texas, United States

Reinecke field is an upper Pennsylvanian to lowest Permian carbonate buildup in the southern part of the Horseshoe Atoll, west Texas, United States. The field and surrounding areas have been imaged with three 3-D seismic surveys and penetrated by many wells. Although Reinecke is commonly referred to as a reefal reservoir, deposition occurred in stratified sequences, 50100 ft (1530 m) thick, dominated by wackestones, packstones, and grainstones. Boundstones (mainly rich in phylloid algae) constitute only 16% of the buildup. Seismic reflectors within the buildup parallel sequence boundaries and are truncated at the margins of the buildup. Three-dimensional seismic surveys show that the top of the Reinecke buildup is highly irregular with more than 470 ft (143 m) of relief. Deep-marine shales overlie the reservoir and act as a seal for this stratigraphic trap. Reinecke's irregular, mounded morphology is the result of localized carbonate growth and erosional truncation. Much of the erosional truncation probably occurred in a deep-marine environment. Reinecke's south dome acts a single continuous reservoir dominated by limestone (70%) with 25% dolomite. Limestone porosity is generally 518% (average of 11.2%) and permeability is 11000 md (average of 166 md). Dolomite porosity is lower (average of 8.3%), but permeability is higher (average of 894 md). Discontinuous low-permeability layers parallel to stratification serve as low-permeability baffles; however, patchy replacive dolomites cut through stratification and act as high-permeability vertical conduits. Good reservoir continuity, low-permeability baffles, and artificially enhanced bottom-water drive helped to recover more than 50% of the original oil in place. Excellent vertical reservoir continuity has allowed implementation of a crestal CO2 flood at Reinecke field. CO2 is being injected into the top of the structure, displacing residual and bypassed mobile oil downward for recovery in lower parts of the reservoir.