RESERVOIR PRESSURE, WATER CHEMISTRY, AND INJECTIVITY OF PROSPECTIVE CO2 SINKS IN OKLAHOMA

Oklahoma contains several large sedimentary basins, including the Anadarko, Arkoma, and Ardmore basins, with considerable potential for geologic storage of CO₂. Prospective reservoirs are stacked in strata ranging in age from Cambrian through Permian and include a spectrum of carbonate and siliciclastic rock types, and in many areas, more than 20 stratigraphic intervals are prospective. Opportunities for storage include saline formations, mature oil and gas reservoirs, and unconventional reservoirs, including coal and shale. Reservoirs are typically severely underpressured to normally pressured, and experience from water injection for brine disposal and waterflooding indicates that many reservoirs accept fluids by simple gravity feed. Surface injection pressure throughout the state is typically <2,000 psi, and calculated bottom-hole pressures are generally between 1,500 and 6,000 psi. Underground sources of drinking water are typically shallower than 500 ft, although deep sources occur locally along major structures. Injectivity ranges widely among reservoirs, and surface injectivity is locally as high as 1,000,000 bbl/d/psi. Values on the order of 100-100,000 bbl/d/psi are typical of most stratigraphic intervals. Accordingly, the subsurface of Oklahoma is well suited for commercial storage of CO₂ in the subsurface. The principal geologic risk to storage is faulting, and seismic prospecting is an important tool for identifying the best sites for storage. Because penecontemporaneous faults predominate, risk is greatest in the Cambrian-Ordovician section and is substantially lower in Pennsylvanian-Permian strata.