Impact of Fault Permeability on Geomechanical Models of CO2 Injection in the Petrel Sub-basin, Northern Australia

The Petrel sub-basin has been assessed as potentially suitable for the geological storage of carbon dioxide. One of the elements required in characterising an area for geological CO2 storage involves geomechanical modelling of the region. A preliminary set of simple geomechanical models were performed to evaluate the risk of fault reactivation and potential degree of uplift for CO2 injection in the Petrel Sub-basin. A number of injection scenarios were run, ranging from likely in situ injection rates (1–5 million tonnes of CO2 per year) to very large injection rates (∼80 million tonnes of CO2 per year). Overall model results suggest that injection at 1 to 5 million tonnes/year does not result in fault reactivation or host rock failure. Partial fault failure can occur at unrealistically high injection rates of 20 million tonnes/year or above. No fault reactivation occurs at any injection rates under strike slip stress conditions, fault reactivation only happens when the stress regime is on the normal fault-strike slip fault boundary. Varying fault permeability by up to two orders of magnitude changes modelled flow patterns, uplift and pore pressure distributions slightly but does not significantly affect fault reactivation potential.