Time Lapse Electrical Resistance During CO2 Storage in a Closed Ended Rock Sample – Dissolution and Mineralization

Abstract Following injection into deep geological formations such as saline aquifers, carbon dioxide (CO2) undergoes a sequence of dynamic and static phases. The dynamic phase encompasses the initial injection and upward migration of CO2 due to buoyancy, forming a gaseous layer beneath the cap rock and above the brine-saturated zone. This configuration may persist for extended periods—ranging from decades to centuries—during which CO2 gradually dissolves into the underlying brine. The rate of dissolution is influenced by factors including brine salinity and the degree of mixing with formation water. Concurrently, mineralization begins when the dissolved CO2 forms a reactive solution capable of dissolving carbonate minerals in the host rock. These long-term geochemical processes are critical to the success of carbon capture and storage (CCS) strategies. Adequate understanding of the response pattern of electrical resistivity logging tools to these processes, mainly dissolution and mineralization of rock minerals, is vital for an effective and long-term monitoring of the injected CO2. This paper presents the response of electrical resistance to first, CO2 displacement of brine in a brine saturated carbonate rock sample, and then the response to the subsequent injection of a CO2-saturated brine to displace brine and CO2 gas, and then the response to a long term (over 30 days) storage of the charged brine in a no flow condition, and then the resultant rock dissolution and mineralization process that ensued during storage period. We observed distinct patterns in the electrical resistance for each of these geochemical processes. Pre- and post- storage analysis conducted on the fluids extracted from the rock sample showed evidence of rock dissolution and mineralization and corroborate the patterns in the electrical resistance observed during storage. XRD analysis conducted on the precipitates observed from the core effluent confirmed the formation of carbonate and few secondary minerals.