It has been reported that deep saline aquifers represent the largest geologic CO<
sub>
2<
/sub>
storage resource. To better predict containment effectiveness and long-term reservoir behavior of these formations, it is important to understand the potential geochemically induced changes to the porosity and permeability of both the primary sealing formation and CO<
sub>
2<
/sub>
storage formation rocks. To investigate these potential changes, an experimental study to probe the geochemical interactions of CO<
sub>
2<
/sub>
/brine/rock system under geologic CO<
sub>
2<
/sub>
storage conditions was conducted in a static reaction system. Marine shale (primary sealing formation) and Lower Tuscaloosa sandstone (CO<
sub>
2<
/sub>
storage formation) core samples taken from the Plant Daniel CO<
sub>
2<
/sub>
storage test site (Jackson County, Mississippi) were exposed to CO<
sub>
2<
/sub>
-saturated brine in a batch reactor at relevant geologic storage conditions (85�C and 23.8 MPa CO<
sub>
2<
/sub>
pressure) for 6 months. X-ray diffraction, scanning electron microscopy, computed tomography, and brine chemistry analyses were performed before and after the exposure. Permeability measurements from the marine shale and sandstone core samples before and after CO<
sub>
2<
/sub>
/brine exposure indicated a significant effective permeability change. Sealing marine shale permeability increased following exposure while the permeability of the sandstone from the storage formation was observed to decrease. Analysis results of the primary sealing formation sample (marine shale) at the Plant Daniel CO<
sub>
2<
/sub>
storage test site have not been reported before. In conclusion, the permeability decrease of the Lower Tuscaloosa sandstone sample reported in this study verifies the results reported in a previous study. These results have implications for the integrity of the primary seal in a CO<
sub>
2<
/sub>
storage setting.