The tomographic inversion of the virtual-source data obtained by processing five days of passive seismic data recorded over the Valhall oil field in Norway demonstrates that reliable information can be obtained on subsurface velocity from passive data. Given the well-established effect of CO2 in decreasing seismic velocities, our results show that passive-seismic monitoring of CCS projects is feasible. The processing of different (overlapping) frequency bands provides velocity information at different depths in the subsurface; lower frequencies image deeper layers. CO2 plumes can thus be tracked as they move upward before they arrive at the surface and create mortal hazards. Analysis of the convergence rate of passive-data correlations towards virtual-source data with signal-to-noise ratio sufficient for tomographic inversion provides useful information on the delay that can be expected between the formation of a CO2 plume and the early warning signal provided by the passive seismic monitoring system. We have recently started the data processing of a new data set recorded over the Long Beach oil field in South California. We plan to process and image these data using a work-flow similar to the one used for the Valhall data. If the results will be equally encouraging, passive-data monitoring of land-based CCS projects will become equally feasible as the one of marine-based projects.
2012 | de Ridder, S., and B. Biondi. Continuous Passive Seismic Monitoring of CCS Projects by Correlating Seismic Noise - A Feasibility Study. In proceedings of the 74th Annual International Conference, European Association of Geoscientists & Engineers.