Rapid High-Resolution Monitoring of Shallow CO2 Controlled Release Experiment: Otway Project Feasibility Study

Abstract

Summary The CO2CRC and its partners are undertaking feasibility studies in preparation for Phase 3 of CO2 controlled release experiment, where CO2 is to be injected in the fault zone at 30–40 m depth. The data analysis from Phase 2 showed that 3D VSP monitoring is feasible for this project. However, a combination of borehole cemented DAS and hydrophones with a surface weight-drop source lacks a good signal resolution for detailed tracking of plume geometry. We propose to utilize reverse 4D VSP method with seismic sensors on the surface and sparker source in the well. This approach will provide ultrahigh resolution and good illumination along with a short survey time: once the system is deployed, we need only repeat shooting in the borehole. We calculated synthetic seismic data for shallow reservoir models of the CO2CRC’s Otway site. Analysis of synthetic data shows that the strength of time-lapse signal is sufficient for confident detection of a small amount of gas. The travel-time difference can be up to 6 ms, which makes data suitable for time-lapse travel-time tomography. Finally, surface receivers provide a good surface coverage, which is beneficial for tracking of the subsurface changes and can be used for quick qualitative monitoring.