THE SMACKOVER FORMATION CARBON DIOXIDE STORAGE ASSESSMENT UNITS IN THE U.S. GULF COAST BASIN

As part of the U.S. Geological Survey National Assessment of Geologic Carbon Dioxide (CO₂) Storage Resources, the Smackover Formation of the U.S. Gulf Coast Basin was evaluated. This evaluation resulted in a Smackover Formation Storage Assessment Unit (SAU) and a Smackover Formation Deep SAU, each with tens of thousands of metric megatons of technically accessible storage resource. The Smackover Formation SAUs consists of those portions of preserved Upper Jurassic carbonate lithology deemed suitable as reservoir for CO₂ sequestration and occurring beneath a regionally extensive seal (the anhydrite of the Buckner Formation and the mudstone of the lower Haynesville Formation). This upper part of the Smackover Formation consists of mostly grain-supported carbonate grainstones, packstones, and boundstones deposited in high-energy shallow-water environments.

The SAU boundaries are defined by the depth below the surface of the storage formation top. Geologic unit picks for the Smackover Formation top reported in a proprietary commercial database help define the extent of the storage interval. The SAU sits between 3,000 and 13,000 feet in depth, and has about a 29-million acre most likely area; whereas the deep SAU sits between 13,000 and 24,000 feet, and has about a 62-million acre most likely area. These interpretations are supported by the basin geologic maps and cross sections in the Geological Society of America’s Decade of North American Geology volume. Regionally, the gross thickness of the Smackover Formation ranges from a few hundred feet (onshore and coastal areas of northeastern Gulf of Mexico) to over a thousand feet (south-southwest of coastal areas). As a result, the SAU gross thickness ranges between 100 and 500 feet, with a net thickness between 50 and 200 feet; and the deep SAU gross thickness ranges between 80 and 400 feet, with a net thickness between 40 and 100 feet. Based on a review of the available literature, the SAU is assigned a porosity range between 10 and 20 percent, whereas the permeability ranges between 0.1 and 1,000 milli-Darcy (mD); and the deep SAU porosity ranges between 8 and 15 percent, whereas the permeability ranges between 0.01 and 500 mD. Water quality data for the SAUs obtained from a published database indicate predominantly saline formation waters.