High-resolution monitoring of CO2 sequestration using walkaway vertical seismic profile and full-waveform inversion

ABSTRACT Applying full-waveform inversion (FWI) to walkway vertical seismic profile (VSP) data provides a promising method for obtaining high-resolution models of subsurface physical properties. Although time-lapse FWI has shown potential for monitoring reservoir changes caused by CO2 storage with high resolution, its application in field data remains scarce due to its vulnerability to nonrepeatable noise. We conduct a field experiment using time-lapse VSP data and FWI to monitor long-term changes in a thin, shallow reservoir due to CO2 injection. We develop a workflow that uses time-lapse FWI for field walkway VSP data to identify time-lapse changes related to less than 60 tons of CO2 injected into a 7 m thick reservoir at a depth of 300 m. A frequency range of 5 to 60 Hz is applied to achieve high-resolution results. This experiment indicates the capability of FWI to perform high-resolution inversion and detect time-lapse anomalies within a shallow reservoir caused by a small amount of CO2 injection. To the best of our knowledge, no similar field experiments have been reported.