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Combined seismic and geoelectrical monitoring and quantification of CO2 geostorage

Daniel Köhn1, Said Attia al Hagrey1, Katharina Benisch1, Sebastian Bauer1, Wolfgang Rabbel1
1 Institut für Geowissenschaften, Universität Kiel

P 11.3 in Wärme-, Energie- und Kohlenstoffspeicherung im Untergrund

 

This paper presents 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. Phase pressures, densities and saturations are obtained from a numerical simulation of the injection process and are introduced into geophysical forward models which simulate the geophysical data acquisition. These synthetic geophysical data 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 (up to 30 m thick) within the target storage formation (~2.2 km depth) from the beginning of the injection process to the end of the post-injection simulation time. Besides the structural mapping of the plume the FWI also delivers the distribution of elastic material parameters within the underground. The mapping capability of ERT technique is enhanced, i.e. limitations of smearing and artefacts are minimized, by: (1) the a priori use of the seismic results to constraint the inversion and, (2) the application of optimized electrode configurations which maximize the resolution.

 

Both geophysical techniques recover the anomaly shape and amplitude accurately reflected by uncertainty analyses of the inversion results.  Using the estimated density, seismic velocity and resistivity models the CO2 saturations within the storage formation are deduced via petrophysical models. Resulting gas saturations from both techniques are in good agreement with each other and with their corresponding input (true) values from the numerical flow simulation. However both methods cannot resolve the CO2 phase fringe of only a few meters thickness. The error of estimated CO2 saturation is 10 % for the FWI method and 13 % for the ERT method. The ERT method profits from joint method application by using structural information from the FWI.

 

 

 

Acknowledgements

 

This study has been carried out within the framework of research projects “CO2Mopa” and “ANGUS+” funded mainly by the German Federal Ministry of Education and Research (BMBF), and partially by EnBWEnergie Baden-Württemberg AG, E.ON Energie AG, E.ON Gas Storage AG, RWE Dea AG, Vattenfall Europe Technology Research GmbH, Wintershall Holding AG and Stadtwerke Kiel.

 

Letzte Änderung 01.11.2013