Amplitude Variation with Offset Responses Modeling Study of Walkaway Vertical Seismic Profile Data at CO2Geological Storage Site, Ketzin, Germany

Abstract

Abstract:An important component of any CO2sequestration project is seismic monitoring for tracking changes in subsurface physical properties, such as velocity and density. Different reservoirs have different amplitude variation with offset (AVO) responses, which can define underground conditions. In the present paper we investigate walkaway vertical seismic profile (VSP) AVO response to CO2injection at the Ketzin site, the first European onshore CO2sequestration pilot study dealing with research on geological storage of CO2. First, we performed rock physics analysis to evaluate the effect of injected CO2on seismic velocity using the Biot‐Gassmann equation. On the basis of this model, the seismic response for different CO2injection saturation was studied using ray tracing modeling. We then created synthetic walkaway VSP data, which we then processed. In contrast, synthetic seismic traces were created from borehole data. Finally, we found that the amplitude of CO2injected sand layer with different gas saturations were increased with the offset when compared with the original brine target layer. This is the typical class III AVO anomaly for gas sand layer. The AVO responses matched the synthetic seismic traces very well. Therefore, walkaway VSP AVO response can monitor CO2distribution in the Ketzin area.