Challenges of resistivity log as a monitoring technique during carbon dioxide sequestration in carbonate formations

Electrical resistivity measurement technique is being used to evaluate the remaining oil in place during carbon dioxide (C02) - EOR and it is currently extended to C02 sequestration projects for tracking and quantifying carbon dioxide migration. Seismic method is another technique but it becomes less effective at about 40% of C02 saturation giving resistivity technique an edge. However, the complexity of carbonate rocks with respect to the heterogeneity of its pore character and wettability, and the susceptibility of these factors to Carbon dioxide - Brine - Rock interaction (CBRI) can make such technique intractable for fluid monitoring in carbonate formations. This paper reviews the suitability of resistivity measurement for carbon dioxide monitoring. We reviewed the factors affecting resistivity-based saturation models with a focus on a new insight into how electrical properties of carbonate formation can be dependent on CBRI and on time. Laboratory study involved injecting supercritical C02 into representative brine saturated core samples under reservoir and a closed boundary condition such that injected C02 remained in place for a considerable length of time. A data acquisition system was designed to log core resistivity, temperature, pore pressure, and overburden pressure with time. Results revealed changes in rocks' pore character and rock electrical behavior over C02 storage time. The resulting effects and challenges on resistivity measurements and estimation of carbon dioxide saturation distribution are also elaborated. Finally, a proposal into addressing these challenges is presented.