Monitoring CO2 response on surface seismic data; a rock physics and seismic modeling feasibility study at the CO2 sequestration site, Ketzin, Germany

An important component of any CO2 sequestration project is seismic monitoring for tracking changes in subsurface physical properties such as velocity and density. Reservoir conditions and CO2 injection quantities govern whether such changes may be observable as a function of time. Here we investigate surface seismic response to CO2 injection at the Ketzin site, the first European onshore CO2 sequestration pilot study dealing with research on geological storage of CO2. First, a rock-physics model was built to evaluate the effect of injected CO2 on the seismic velocity. On the basis of this model, the seismic response for different CO2 injection geometries and saturation was studied using 1D elastic modeling and 2D acoustic finite difference modeling. Rock-physics models show that CO2 injected in a gaseous state, rather than in a supercritical state, will have a more pronounced effect on seismic velocity, resulting in a stronger CO2 response. However, reservoir heterogeneity and seismic resolution, as well as random and coherent seismic noise, are negative factors that need to be considered in a seismic monitoring program. In spite of these potential difficulties, our seismic modeling results indicate that the CO2 seismic response should be strong enough to allow tracking on surface seismic data. Amplitude-related attributes (i.e., acoustic impedance versus Poisson's ratio cross-plots) and time-shift measurements are shown to be suitable methods for CO2 monitoring. (C) 2010 Elsevier B.V. All rights reserved.