Mass-balance threshold matching of geoelectric and seismic data: a case study from Ketzin

Seismic and geoelectric methods are used as complementary tools for the identification of fluid/gas effects in underground storage and production scenarios. Both methods present a different resolution. Seismic data tend to be acquired by much more dense geometrical layouts, and geoelectric acquisition as a potential field method shows information integrated over spatial distances. We present results matching seismic and electrical resistivity tomography (ERT) results from two repeat surveys performed during CO 2 storage operations at the Ketzin pilot site in Germany. The approach is based on data acquired in 2009 and 2012 at different stages of total injected CO 2 volume. Masses are obtained from the averaged change in acoustic impedance and are compared to masses inferred from inverted electrical resistivities. Archie's equation is used to obtain saturations from the ERT models. The sensitivity of the background resistivity, R 0 , as a relevant parameter in determining the mass of injected CO 2 is analysed. A specific threshold analysis based on seismic thickness by bin has been applied to investigate the matching of seismically and ERT obtained masses. Both mass estimates match comparatively well, but show inherent sensitive parameters and their corresponding impact as temporal and spatial uncertainties that may cause mass differences for the areas of investigation.