On the Design of Cross-hole Resistivity Arrays for High-resolution and Cost-effective Storage Reservoir Monitoring

Electrical resistivity tomography (ERT) has received consideration as a tool for permanent monitoring of saline storage reservoirs due to its high sensitivity to compositional pore fluid changes. The information content offered by geoelectrical data is ultimately limited by the electrode arrangement, and consequently, its full exploitation requires a well-conceived experimental design. We present a methodology to estimate an optimum number of electrodes as well as their specific locations along the borehole trajectories based on a maximization of the respective model resolution. Using a synthetic example analogous to the Ketzin site, Germany, we demonstrate that relatively sparse optimized setups with a refinement of the electrode spacings in the target horizon can offer comparable tomographic imaging capabilities with regard to rather dense arrays. The approach presented can assist practitioners with the design of high-resolution and cost-effective down-hole installations at future CO2 storage sites.