We performed time-lapse surface-wave analysis to monitor the shallow subsurface at the Aquistore CO2 storage site, managed by the Petroleum Technology Research Centre, Canada. A continuous and controlled seismic source system called the Accurately Controlled Routinely Operated Signal System (ACROSS) is used to enhance the temporal resolution and source repeatability in the monitoring. We extracted hourly-variation of surface-wave phase velocities from continuous seismic data with 4 hour stacking. As a result, we could monitor phase velocities within 1 % accuracy during 1-9 days in the frequency range of 4.5-6 Hz. We identified 2-5 % seasonal variation of phase velocities. The high phase velocities observed in winter can be explained by the degree of freezing of partially saturated rock. Our time-lapse results contributed to improving the accuracy of monitoring deep reflections from the CO2 injection reservoir by correcting seasonal variations of near-surface velocity. The high temporal resolution and accuracy of our monitoring results have the potential to identify sudden changes such as CO2 leakage from CO2 storage sites.
|Title of host publication||SEG Technical Program Expanded Abstracts 2016|
|Publication status||Published - Sep 1 2016|