Box experiments on monitoring the CO2 migration in a homogeneous medium using electrical resistivity survey

Geological sequestration of CO 2 necessarily involves reliable techniques for monitoring the migration of CO 2 injected in deep formations. In this study, a series of lab-scale experiments was conducted to investigate the feasibility of geochemical sampling and electrical resistivity survey in imaging and characterizing various phases of CO 2 in a homogeneous medium. An acryl box packed with 1-mm dia. glass beads was used as the brine aquifer for CO 2 sequestration. Two phases of CO 2 and a supercritical CO 2 substitute were applied in a series of injection processes in modified experiments for simulating CO 2 sequestration. As well as porewater analysis, time-lapse electrical resistivity survey was performed with electrodes positioned on the box. For reconstructing two-dimensional resistivity images, electrical potential differences were measured at potential dipoles on the top surface of the box. To investigate the spatial and temporal evolution of the plume of injecting fluids, 2D resultant resistivity images at specified time were compared with discrete distributions of CO 2 concentration in the box. In the experiment of CO 2 gas, the time-lapse resistivity images showed the distinct increase in resistivity and suggested that the sequential changes in electrical resistivity images could be acquired when the CO 2 gas plume migrates in deep brine aquifers. In the experiment of supercritical CO 2 substitute, the time-lapse resistivity images showed that injected KF-50 was kept afloat by buoyancy, which accumulated under the impermeable layer in free phase, and leaked somewhat to the surface. The electrical resistivity survey can be successfully detect the heterogeneous and localized distributions of supercritical CO 2 in deep brine aquifers, implying that the electrical resistivity tomography could be a useful technical option for monitoring CO 2 during geological sequestration.