Reflection Seismic and Borehole Geoelectric Numerical Modeling for CCS Monitoring - the Role of Petrophysical and other Parameters

The research project “CO2 MoPa” (modeling and parameterization of CO2 storage in deep saline formations for dimensions and risk analysis) has been initiated in 2008 by partners from different disciplines (e.g. geology, hydrogeology, geochemistry, geophysics, geomechanics, hydraulic engineering and law). It deals with the parameterization of virtual subsurface storage sites to characterize rock properties, with high pressure-temperature experiments to determine in situ hydro-petrophysical and mechanical parameters, and with modeling of processes related to CCS in deep saline reservoirs. One objective is the estimation of the sensitivity and the resolution of reflection seismic and geoelectrical time-lapse measurements in order to determine the underground distribution of CO2. Compared with seismic, electric resistivity tomography (ERT) has lower resolution, but its permanent installation and continuous monitoring can make it an economical alternative or complement. Seismic and ERT (in boreholes) applications to quantify changes of intrinsic aquifer properties with time are justified by the velocity and resistivity decrease related to CO2 injection. Our numerical modeling reveals the capability of the techniques to map CO2 plumes and changes as a function of thickness, CO2 concentration, receiver/electrode configuration, aspect ratio, and modeling and inversion constraint parameters. The amplitude of the seismic wave reflected from the caprock-CO2 boundary depends on a variety of parameters influencing the seismic impedance such as porosity, seismic velocities of caprock and reservoir rock before injection, density, pressure, temperature and salinity. Since brine and CO2 velocity and density are pressure and temperature dependent, reflection coefficient changes with CO2 concentration are also depth dependent. The changes of the reflection coefficient with increasing CO2 concentration are most pronounced for low concentrations while the changes of electric resistivity with increasing CO2 concentration are highest for high concentrations. This study is funded by the German Federal Ministry of Education and Research (BMBF), EnBW Energie Baden-Württemberg AG, E.ON Energie AG, E.ON Ruhrgas AG, RWE Dea AG, Vattenfall Europe Technology Research GmbH, Wintershall Holding AG and Stadtwerke Kiel AG as part of the CO2-MoPa joint project in the framework of the Special Program GEOTECHNOLOGIEN.