4D Imaging of the Ketzin CO2 Storage Site (Germany) Using a Combination of Seismic and Electrical Resistivity Imaging

A combination of seismic and geoelectric processing is presented using a structurally constrained inversion approach. Structural constraints are interpreted from seismic data and inserted into the geoelectric inversion through a local regularisation, which allows inverted resistivities to behave also discontinuously across these a priori constraints. This sequential arrangement of seismic processing and constrained resistivity inversion makes the generic assumption that the petrophysical parameters of both methods change across common lithostructural boundaries. We evaluate the approach using a numerical example and a real 4D data example from the CO2 pilot storage site, Ketzin, Germany. The real data case shows that the time-lapse anomalies, which have independently been imaged by surface seismic and surface-downhole geoelectric methods, correlate well at the CO2-flooded reservoir. However, at some distance to the downhole electrodes the geoelectric images provide a notably lower resolution in comparison to the corresponding seismic images. The results demonstrate the relevance of the presented approach for the combination of both methods in geophysical CO2 storage monitoring operations.