Field-Scale Geomechanical Assessment of CO2 Injection in a Depleted Gas Reservoir in the North Malay Basin

Abstract

A field-scale geomechanical assessment was conducted for a depleted gas reservoir in the North Malay Basin, offshore Malaysia, that has been repurposed for CO2 storage. A coupled finite element geomechanical model and dynamic reservoir flow simulation were developed to evaluate caprock integrity and fault stability during CO2 injection. To quantify geomechanical uncertainty, a series of sensitivity analyses were performed, focusing on variations in the mechanical properties of both the storage formation and the overlying caprock. The simulation results indicate that caprock integrity and fault stability are maintained under the planned CO2 injection conditions. Sensitivity analyses show that uncertainties in the mechanical properties of the storage formation and caprock have a limited impact on geomechanical performance. The risk of caprock fracturing remains low because injection-induced pore pressure increases do not exceed the corresponding fracture initiation pressure of the caprock. Fault stability evaluations, based on shear stress analyses along fault surfaces, demonstrate that the Tau-ratio (defined as shear stress divided by shear strength) remains below unity in all simulated scenarios, indicating no predicted fault reactivation. Although localized areas near injection wells close to the structural crest and in proximity to faults exhibit relatively elevated failure potential, the overall geomechanical risk remains low. The results demonstrate that uncertainties in the mechanical properties of the storage formation and caprock have minimal influence on containment performance, supporting the conclusion that injected CO2 remains securely contained within the target storage interval under the evaluated operating conditions.