CAPROCK INTERACTIONS WITH SUPERCRITICAL CO2 AND BRINE: A LABORATORY STUDY OF THE EFFECTS OF SIMULATED GEOLOGICAL CO2 SEQUESTRATION ON SHALES FROM THE BLACK WARRIOR RIVER BASIN, ALABAMA

To evaluate the risks associated with geologic CO₂ sequestration, a better understanding of the interaction of brine-rock-supercritical CO₂ is needed. The geochemical effects of brine and supercritical CO_­2 on two reservoir caprocks in the Black Warrior River Basin, the Pottsville and Parkwood Formations, were examined via laboratory modeling of in situ conditions. The clay fraction was separated from the caprocks and treated at ~ 100 bar and 363 K to simulate injection conditions at depth. Supercritical CO₂ was attained by using dry ice in a high pressure acid digestion vessel. Samples were observed using XRD, WD-XRF, AA, SEM, and EDS. Clay fractions from both formations contain some smectite, illite, kaolinite and quartz. Results show the dissolution of illite, CO₂-brine induced cation exchange of K⁺, and the dissolution of silicate minerals as a product of interaction with supercritical CO₂.