Structural and Stratigraphic Controls on Storage and CO2 EOR Potential in Major Basins in Texas, California, Illinois, and Michigan

William A. Ambrose¹, Mark H. Holtz¹, Vanessa Núñez-López¹, Susan D. Hovorka¹, Edgar H. Guevara¹, Caroline Breton¹, and Charles Christopher^2
1 Bureau of Economic Geology, Austin, TX
² BP America, Inc, Houston, TX

The potential for CO2 injectivity, storage, and EOR is controlled partly by structural and stratigraphic heterogeneity. The capacity for sequestration of CO2 can be enhanced in heterogeneous reservoirs because of longer flow paths and increased interaction of CO2 with a larger fraction of the rock volume, although this capacity can be offset by lower effective porosity owing to multiple shaly interbeds. Conversely, CO2 sequestration can be reduced in homogenous reservoirs, where buoyancy limits flow paths to thin sheets. A relative ranking of CO2 injectivity and storage in selected fields in the Los Angeles Basin, Illinois Basin, Michigan Basin, and Texas Gulf Coast was done by assessing their relative degree of structural and stratigraphic heterogeneity and other factors, such as thickness, temperature, and pressure. Stratigraphically complex, deep-water reservoirs in the Los Angeles Basin are faulted and folded, and many southeast Texas Frio reservoirs have high structural complexity because of faults around salt domes. Wave-modified deltaic Frio reservoirs have good waterflood sweep efficiencies and potentially high storage volumes. Although many reservoirs in the Illinois and Michigan Basins are structurally simple and occur in fault-bounded anticlinal traps, they are stratigraphically complex, containing mixed clastic-carbonate pay zones in grainstone, oolite-shoal, and tidal-inlet deposits. CO2 injectivity may be favorable locally in permeable and laterally extensive tidal-bar deposits in the Aux Vases Sandstone, but local permeability pinch-outs may limit one's ability to predict migration pathways. Although geological heterogeneity may increase residence time, risk of seal failure by faults requires additional data collection and modeling.