Identifying the viability of rock formations to successfully limit the upward migration of carbon dioxide (CO2) is vital for carbon storage permanence. As an attempt to address increasing atmospheric concentrations of CO2, CO2 is captured in industrial settings, compressed to a supercritical state (at least 31 °C, 88 °F and 7.38 MPa, 1070 psi), and is eventually injected deep beneath the surface between 0.8 to 1.0 kilometers (2,625 to 3,280 feet), often in saline reservoirs where CO2 will remain in a dense and stable plume. However, carbon dioxide is a buoyant fluid and will migrate upward through the subsurface until it reaches an impermeable seal which the CO2 may react with. Typical seals in geologic reservoirs are shales due to their low porosities and permeabilities, however limestones can exhibit similar measurements. This work examines the effect supercritical CO2 has on potential sealing rock layers within the Michigan Basin, namely the early Devonian Amherstberg limestone formation, which may be largely responsible for sealing sequestered carbon dioxide within underlying rock units. In this study, core samples retrieved from an experimental injection well located in Otsego County, Michigan were exposed to supercritical CO2 and synthetic formation brine at reservoir pressure and temperature conditions. Scanning Electron Microscopy (SEM) analyses were performed on core samples exposed to dry CO2 and CO2-saturated brine to compare surface alterations before and after fluid-rock reactions. X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS) aided SEM analyses to characterize geochemical changes within the rock sample. Fresh and reacted synthetic brine samples were analyzed using ICP-OES to determine changes in elemental concentration. Findings indicate that calcium carbonate phases are more sensitive to CO2-saturated brine interactions rather than CO2 interactions alone, and surface mesoporosity visibly enlarged in regions where such phases reside. In addition, salt and calcium carbonate minerals precipitated out of solution during reactions onto etched rock surfaces resulting in regions of decreased porosity. These findings suggest that CO2-brine interactions with the Amherstberg Limestone may not reach geochemical equilibrium, shedding light on the potential instability of CO2 storage within carbonate caprock reservoir systems
