CO2 SEQUESTRATION POTENTIAL OF MIOCENE SANDSTONE RESERVOIRS, OFFSHORE TEXAS STATE WATERS, GULF OF MEXICO

We are evaluating the CO₂ sequestration potential of Miocene sandstone reservoirs in Texas State Waters off Matagorda Peninsula, Gulf of Mexico Basin. Our data set consists of wireline logs, core, paleontological data, and thin sections selected from 57 wells in a 110 mi² area (71 acres; 285 km²). These data were analyzed to estimate capacity and feasibility of utilization of Miocene strata for CO₂ disposal/storage. The wells are located 6-10 miles (9.6-16 km) from the Texas shoreline in water depths of 50-70 ft (15-21 m). Thick, porous and permeable Miocene target reservoirs occur between 8,800 and 11,000 ft (2,682 and 3,353 m; measured depth). A Lower Miocene core was available from the Amoco Production State Tract 487-L SW/4 #2 well (14,840-15,150 ft or 4,523-4,617 m; measured depth). Although this specific reservoir may be too deep for CO₂ sequestration, it nonetheless serves as a useful sedimentological analogue. The cored interval (310 ft; 95 m) sampled most of the quartz-rich, fine-grained sandstone reservoir that occurs within a 1,200-ft (366 m) thick, upward-coarsening progradational unit. The unit represents an amalgamation of many individual high-frequency delta progradation episodes, each made up of a coarsening-upward sandstone succession bounded by silty facies. Four major facies (and inferred environments) were observed in the core: (1) well sorted, fine-medium grained, parallel laminated to massive quartz (deltaic channel mouth bar); (2) well sorted, fine-medium grained, parallel-laminated to trough cross-bedded quartz sandstone that exhibits a fining-upward grain-size trend overlying a sharp, erosive base (deltaic distributary channel fill); (3) moderately to poorly sorted, very fine-grained, silty sandstones with moderate to low poroperm (abandoned deltaic distributary channel); (4) moderately to poorly sorted, silty, very fine-grained, thinly parallel-laminated, occasionally deformed sandstones with low poroperm (abandoned delta lobe). Offshore Miocene sandstone reservoirs in Texas State Waters provide a unique and potentially vast resource for CO₂ sequestration in the United States.