3D ERT in Boreholes for Mapping CAES Plume in Saline Aquifers

Renewable energy resources are intermittent and need buffer storage to the bridge time-gap between production and demand peaks. North German Basin has a very large capacity for CAES in saline aquifers and cavities. Replacement of brine by gas in aquifer cause strong changes in electrical resistivity. Previously we have shown the applicability of 2D electric resistivity tomography (ERT) for monitoring sequestered CO2 in these reservoirs. Towards more real world problems, this paper aims at studying resolution of 3D ERT in boreholes for CAES mapping in deep saline aquifers. We used for this 3D surveys 3-9 vertical arrays of borehole electrodes installed surrounding the targets (caprock, aquifer, CAES plume, aquitard). We applied non classical electrode configurations of pseudo (optimized) and real 3D measurements in different boreholes. The results show that the applied 3D technique can generally map the dome structure targets with varying resolution, smearing and artefacts. However, resistivity amplitudes are less correctly recovered. The resolution increases with increasing number of borehole electrode arrays, increasing of layer thicknesses and the a priori fixing of boundaries in the inversion. Optimized 2D arrays have better resolution than the other arrays and thus needs to be developed to real 3D arrays.