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

Abstract

Geological sequestration of CO2 necessarily involves reliable techniques for monitoring the migration of CO2 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 CO2 in a homogeneous medium. An acryl box packed with 1-mm dia. glass beads was used as the brine aquifer for CO2 sequestration. Two phases of CO2 and a supercritical CO2 substitute were applied in a series of injection processes in modified experiments for simulating CO2 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 CO2 concentration in the box. In the experiment of CO2 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 CO2 gas plume migrates in deep brine aquifers. In the experiment of supercritical CO2 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 CO2 in deep brine aquifers, implying that the electrical resistivity tomography could be a useful technical option for monitoring CO2 during geological sequestration.