The CO2CRC Otway shallow CO 2 controlled release experiment: Fault characterization and geophysical monitoring design

CO2CRC has made a significant investment into establishing the feasibility of conducting a CO 2 injection experiment into a shallow fault at the CO2CRC Otway International Test Centre. Two appraisal wells drilled and cored through Brumbys Fault indicate the fault extends to the base of the upper 2 m thick Hesse Clay layer, which forms a seal to the underlying Port Campbell Limestone aquifer. The fault does not have a defined core; rather, it is expressed by an approximately 6-10 m wide cataclastic zone. Permeability within the Port Campbell Limestone is variable, ranging from tens to thousands of millidarcies (10 −14 to 10 −12 m 2 ). The rock strength is low and it is recommended to conduct the experiment at approximately 80 m depth rather than the 40 m originally proposed. This provides more confining pressure and will ensure that the injection pressure does not exceed the fracture pressure. A deeper injection also provides better spatial and timing conditions for geophysical monitoring and tracking of the CO 2 plume. Simulations indicate that a 10 t CO 2 injection experiment would be sufficient to monitor CO 2 migration using geophysical techniques and the planned deployment of reverse 4D vertical seismic profiling would be able to track this small quantity of CO 2 up a fault. In addition to providing an opportunity to demonstrate semi-continuous, near real-time monitoring of CO 2 migration up a fault, the planned CO 2 injection experiment presents a unique opportunity to obtain field measurements on vertical fault permeability at a shallow strike-slip fault.