RESERVOIR PROPERTIES OF THE LOWER SAN ANDRES FORMATION ON THE NORTHWEST SHELF OF THE PERMIAN BASIN

The early Permian San Andres Formation is one of the most productive oil and gas reservoirs in the Permian Basin. Throughout much of the basin the Lower San Andres reservoirs have been swept by natural waters leading to intense dolomitization, karst overprinting, and the formation of large residual oil zones (ROZs) beneath pay zones. These ROZs have been the target of enhanced oil recovery (EOR) utilizing CO₂, which can ultimately sequester up to 80% of the CO₂ utilized in the project. The incidental CO₂ storage capacity of the San Andres Formation provides a large opportunity for reducing CO₂ emissions within the oil and gas industry. Broadening our understanding of reservoir properties (thickness, porosity, permeability, etc.) is essential for developing or converting projects in the San Andres Formation utilizing CO₂. To further constrain the residual oil zone of the Northwest Shelf in Cochran and Yoakum Counties, Texas approximately 300 ft (90 m) of lower San Andres core recovered from the Mammoth Exploration Hudson 601H well in the Blowing Sand Field. The cored interval is from −5362 to −5060 ft (−1542 to −1634 m) below surface indicating sufficient depth to maintain supercritical CO₂ in the reservoir. Eight distinct carbonate facies from outer shelf mudstones to supratidal evaporites have been identified through the study of the core and petrographic thin sections. Outer- and mid-shelf packstones, shallow subtidal wackestone, and ooid shoals are identified as reservoir facies, whereas outer shelf laminated mudstone, intertidal wackestone, and evaporites provide baffles to flow and seal the reservoir. Thin section porosity and log-based porosity indicates 4 porosity zones present in the cored interval. Air permeability values range from 0.002 to 40.873 mD. Together the petrologic, petrographic, petrophysical, and core analyses from the Hudson 601H provide key inputs for development of a reservoir geo-model for the Lower San Andres Formation when combined with log data from surrounding wells. This work also allows for calculation of potential recoverable oil from the porosity zones in the ROZ as well as estimates of potential CO₂ storage in the Lower San Andres Formation on the Northwest Shelf.