Fault-seal Risk Analysis for CO2 Storage in the Petrel Sub-basin, NW Australia

This geomechanical analysis of the faults in the Petrel sub-basin, NW Australia, aimed to constrain the in-situ stresses and rock strength and to evaluate the risk of fault reactivation and leakage. The risk of reactivation (in terms of stress ratios such as Slip Tendency) was highest on faults orientated in an approximately east-west direction. However, a fault intersecting a shallow reservoir has a lower stress state and requires a smaller increase in pore pressure to induce failure (Slip Stability), even if not optimally oriented. Pore-pressure increases during CO2 injection of <5MPa could therefore potentially cause leakage up those faults in the shallowest eastern part the study area. The broader basin prospectivity assessment, of which this study is only a part, has found that within the western areas of highest potential for CO2 injection and storage the risk of failure along identified faults is low. Furthermore, injection simulation modelling has shown that pore-pressure under typical injection conditions and parameters would not approach the pressure required to cause fault leakage.