Abstract
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 field time-lapse VSP data. The coda-wave interferometry method can estimate relative temporal changes in seismic velocities. 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 time-lapse VSP data along three azimuthal directions with different offset ranges from the observation well are used in this study. Generally, the estimated mean velocity changes from field VSP data from different shots show similar changing pattern with receiver depth. Mid offset shots (shot 5, 6, and 8) give largest estimation, while closest offset shots (shot 1, 2, and 4) give mid estimated changes and shot 9 with offset 1.5km give smallest estimated velocity changes. The estimated velocity changes are as large as 0.5%. This demonstrates that the coda-wave interferometry method can be used for monitoring of CO2 injection using time-lapse VSP data. The different changes along different azimuths may be caused by the local geology heterogeneity.
Published Version
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