Combined Seismic Waveform Inversion and Geoelectrical Monitoring for CO2 Storage Using a Synthetic Field Site

We present the application and verification of a combined geophysical approach for monitoring and quantifying the storage of CO2 in deep saline formations using numerical simulations. Supercritical CO2 is injected into a deep thin saline aquifer below a synthetic site of the North German Basin. The displacement of formation brine by CO2 yields changes in bulk density, elastic moduli and electric resistivity. This justifies the application of the seismic full waveform inversion (FWI) and electric resistivity tomography (ERT) to monitor and quantify the thin, deep gas plume. These goals are real challenges for the applied geophysical monitoring techniques. Densities and saturations are obtained from a numerical simulation of the injection process and are introduced into geophysical forward models to simulate the geophysical data acquisition. These synthetic geophysical datasets are then inverted and evaluated with respect to changes in CO2 saturation and are compared to the fully known CO2 saturation of the numerical process model. Inversion results show that both seismic FWI as well as ERT techniques are capable to detect and map the thin CO2 phase body within the target storage formation (~2.2 km depth) from the beginning of the injection process, if accurate baseline models are available.