Numerical modeling of time-lapse monitoring of CO₂ sequestration in a layered basalt reservoir

As part of preparations in plans by The Big Sky Carbon Sequestration Partnership (BSCSP) to inject CO₂ in layered basalt, we numerically investigate seismic methods as a noninvasive monitoring technique. Basalt seems to have geochemical advantages as a reservoir for CO₂ storage (CO₂ mineral-izes quite rapidly while exposed to basalt), but poses a considerable challenge in term of seismic monitoring: strong scattering from the layering of the basalt complicates surface seismic imaging. We perform numerical tests using the Spectral Element Method (SEM) to identify possibilities and limitations of seismic monitoring of CO₂ sequestration in a basalt reservoir. While surface seismic is unlikely to detect small physical changes in the reservoir due to the injection of CO₂, the results from Vertical Seismic Profiling (VSP) simulations are encouraging. As a perturbation, we make a 5% change in wave velocity, which produces significant changes in VSP images of pre-injection and post-injection conditions. Finally, we perform an analysis using Coda Wave Interferometry (CWI), to quantify these changes in the reservoir properties due to CO₂ injection.