Monitoring CO 2 sequestration into deep saline aquifer and associated salt intrusion using coupled multiphase flow modeling and time‐lapse electrical resistivity tomography

Successful geological storage and sequestration of carbon dioxide (CO 2 ) require efficient monitoring of the migration of CO 2 plume during and after large‐scale injection in order to verify the containment of the injected CO 2 within the target formation and to evaluate potential leakage risk. Field studies have shown that surface and cross‐borehole electrical resistivity tomography (ERT) can be a useful tool in imaging and characterizing solute transport in heterogeneous subsurface. In this synthetic study, we have coupled a 3‐D multiphase flow model with a parallel 3‐D time‐lapse ERT inversion code to explore the feasibility of using time‐lapse ERT for simultaneously monitoring the migration of CO 2 plume in deep saline formation and potential brine intrusion into shallow fresh water aquifer. Direct comparisons of the inverted CO 2 plumes resulting from ERT with multiphase flow simulation results indicate the ERT could be used to delineate the migration of CO 2 plume. Detailed comparisons on the locations, sizes and shapes of CO 2 plume and intruded brine plumes suggest that ERT inversion tends to underestimate the area review of the CO 2 plume, but overestimate the thickness and total volume of the CO2 plume. The total volume of intruded brine plumes is overestimated as well. However, all discrepancies remain within reasonable ranges. Our study suggests that time‐lapse ERT is a useful monitoring tool in characterizing the movement of injected CO 2 into deep saline aquifer and detecting potential brine intrusion under large‐scale field injection conditions.