Interpretation of Time-lapse Surface Seismic Data at a CO2 Injection Site, Violet Grove, Alberta
Time-lapse seismic technology has been implemented at the Violet Grove CO2 injection pilot to monitor the CO2 injection and storage in the Cardium Formation. A multi-component 2.5D surface seismic baseline survey was acquired in March 2005, prior to CO2 injection; after 9 months of CO2 injection, the first monitor multicomponent surface seismic survey was acquired in December 2005.
Different time-lapse analysis methods, such as time shift, amplitude difference, Vp/Vs, post-stack impedance inversion, and AVO, were tested. Subtle changes at the Cardium Sand in the PS data and P-wave impedance inversion were found along Line 1 between the monitor and baseline surveys, but differences on Line 2 and 3 and in the 3D volume were less clear.
The analysis showed no significant changes in the seismic data above the reservoir, from which it is interpreted that no leakage is occurring from the reservoir. The lack of predicted anomalies at the Cardium level indicates also that the CO2 is probably confined to a thin layer (<6m) of porous sand in the Cardium Formation.