Monitoring of Geological Carbon Sequestration Using the Coda-wave Interferometry Method and Time-lapse VSP Data

Injection and movement/saturation of CO2 in a geological formation can cause changes in seismic velocities and attenuation, resulting in changes in seismic-wave scattering and propagation. Accurately estimating seismic-velocity changes from time-lapse seismograms can provide valuable information about where CO2 moves. We investigate the capability of the coda-wave interferometry method for monitoring geological carbon sequestration using synthetic and field time-lapse VSP data. The coda-wave interferometry method can estimate relative temporal changes in seismic velocities. Synthetic time-lapse VSP data sets were generated using a finite-difference elastic-wave equation scheme for a CO2 injection scenario and a possible leakage scenario. Pre-injection and post-injection field VSP data sets were acquired for monitoring of injected CO2 in a brine aquifer. We estimate the temporal velocity changes at the centers of a moving time window using the coda-wave interferometry method, and then obtain the mean velocity change by averaging the temporal velocity changes over time. The estimated mean velocity changes, from both synthetic and field VSP data, increase significantly for receiver positions approaching the top of a CO2 reservoir. This demonstrates that the coda-wave interferometry method can be used for reliable monitoring of CO2 injection using time-lapse VSP data.