Time Lapse VSP Program for Otway Basin CO2 Sequestration Pilot Project

The Australian Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) is currently undertaking the Otway Basin Pilot Project, which involves the injection and storage of 100,000 tonnes of carbon dioxide within the subsurface. The Otway Project is the first of its kind, where CO2 injection will be into a depleted gas reservoir and, therefore, the project will provide important experience for monitoring and verification under these conditions. The overall complexity of the field, its depth, small size and the presence of free and residual gas zones present a serious challenge for 4D seismic monitoring. Accordingly, we adopted a monitoring strategy which combines surface and borehole seismic measurements that optimises our ability to verify CO2 containment. Design of the monitoring program involved numerical modelling and, crucially, pilot field tests. Of particular interest was the application of borehole seismic methods as they can provide better resolution, higher signal to noise ratio and superior repeatability in comparison to surface seismic data. Data recorded from several test VSP surveys and 3D base line VSP survey are analysed for quality, consistency and repeatability.