This work explores, using reservoir simulation, the impact of reservoir architecture on CO2 plume movement and the reservoir's storage capacity. Subsurface flow of CO2 in the presence of shale "baffles", or lack thereof, will be reviewed in conjunction with other reservoir characteristics that influence flow such as formation dip, capillary pressure, pore volume trapping, and the rate of CO2 dissolution. Recent geologic and reservoir data collected from the Tuscaloosa Formation at the Mississippi Test Site (a Southeastern Regional Carbon Sequestration Partnership CO2 sequestration pilot test) will be used as the case study for evaluating alternative CO2 storage engineering concepts for maximizing CO2 storage capacity. The Tuscaloosa Formation is a thick, porous, permeable, regionally extensive saline reservoir occurring throughout the Gulf Coast and is considered a promising target for large-scale CO2 storage.
Because of its natural buoyancy, CO2 tends to rise to the crest of a saline reservoir following its injection, where a cap rock prevents further vertical migration. This buoyancy phenomenon can lead to low contact between the CO2 injectant and the reservoir's brine fluids and pore space, limiting usable storage capacity and increasing the plume's areal extent. One way that vertical flow of injected CO2 can be mitigated is to take advantage of reservoir architecture, i.e., the natural horizontal shale breaks or "baffles" within a storage formation to distribute the injectant vertically. While some of these shale intervals may not be permanent seals, they may have the capacity to constrain or distribute vertical flow, creating additional contact between the CO2 and the saline formation, thus achieving increased storage capacity and CO2 plume concentration, while limiting the plume's areal extent.