Double-difference seismic tomography is performed on a carbon sequestration operation in the Aneth Oil Field in southeast Utah as part of a Department of Energy initiative on monitoring, verification, and accounting of sequestered CO2. A total of 1,211 seismic events were recorded from a borehole array of 22 geophones. Aneth Unit data were divided into four time periods for time-lapse analysis. A low velocity zone spanning the lateral extents of the observable region, likely representing a CO2 plume, is detected when considering voxels containing the highest ray path coverage. A series of synthetic tomography tests simulating different CO2 plume sizes and locations was performed to assist in characterizing velocity changes associated with Aneth Unit data. Inferences about the existence of a CO2 plume should be made by comparing actual data to synthetic data resulting from simulations performed under similar conditions. Considering synthetic simulation similarities and a derivative weight sum analysis, a CO2 plume can be imaged within the Desert Creek reservoir, but the resolution of the CO2 plume is too low for proper monitoring, verification, and accounting of injected CO2. Recommendations, for improving CO2 plume resolution through double difference seismic tomography, are made to increase the ray path distribution throughout the Aneth Unit by varying geophone locations.

Master of Science