PREDICTION OF BASIN-SCALE CARBON DIOXIDE STORAGE POTENTIAL IN CARBONATE AND SILICICLASTIC RESERVOIRS OF THE GULF OF MEXICO BASIN

Carbon dioxide (CO₂) capture and storage (CCS) in geologic formations is intended to reduce anthropogenic CO₂ emissions, and involves capturing CO₂ from stationary sources and injecting it into geologic storage (GS) units, such as oil and gas reservoirs. The U.S. Geological Survey is conducting a national assessment of potential GS reservoirs, called storage assessment units (SAUs), on a regional to sub-basinal scale. The SAUs are identified based upon geologic properties such as high reservoir porosity, a minimum drilling depth of ~900 meters (3,000 feet), and the presence of a regional seal. Published literature, borehole data, and geologic maps are used to interpret and evaluate the depositional environment, basin structure, and trapping mechanisms for an SAU. These data are also used to predict lithologic variability, distributions of porosity and permeability, gross and net-porous thickness, and lateral extent. Data availability controls the level to which the geologist must rely on predictive methods to make stratigraphic interpretations and infer the rock properties of SAUs and their boundaries. Applied stratigraphic prediction techniques include: 1) the evaluation of sequence stratigraphy and facies distribution in siliciclastic units to predict rock properties and SAU boundaries, as well as predict the effectiveness and integrity of SAU seals; 2) employing porosity decline with depth correlations to predict the porosity of deep SAUs; and 3) applying knowledge of pre- and post-burial carbonate diagenesis to predict the porosity, permeability, and extent of porous intervals within a carbonate-rich SAU. Geologic analogs can also be employed to strengthen and test predictive techniques. The Gulf of Mexico Basin is a major petroleum province with numerous play types, as well as many coal-fired power plants, making it a strong candidate for CCS. Uplifts, fault systems, and fluctuations in relative sea level throughout history have made this a geologically complex basin. Twenty-eight SAUs have been identified in carbonate and siliciclastic reservoirs in the basin, which were delineated based upon varying reliance on predictive methods relative to data availability and geologic complexity in a given region.