Effects of Isothermal vs Thermal Simulation in 3D/4D CCS Geomechanical Containment Risk Evaluation for a Depleted Clastic Reservoir

Abstract A depleted multi-stacked clastic reservoir has been selected as a potential CO2 sequestration site. As part of the storage development plan, understanding the geomechanical implications of isothermal and thermal conditions in coupled geomechanical modelling is critical for optimizing CO2 storage strategies. This study investigates the overall geomechanical risk and caprock integrity assessment of both isothermal and thermal simulations by evaluating the results of fault stability analysis, caprock integrity assessment and reservoir compaction-expansion and seabed subsidence-uplift for both cases. The impact of thermal effects on caprock integrity is also further investigated by analysing the potential of hydraulic fracture initiation and propagation in the reservoir and caprock. The results of the thermal model showed that there is significant temperature and stress changes in the reservoir and caprock observed at the injector wells. The modelling results suggest that although there is no impact to the base case storage scenario in terms of caprock integrity risks, there are some impacts observed in the high case storage scenario with a slight reduction of caprock pressure margin in the overlying regional seals. Both cases showed low geomechanical risks of fault re-activation as the faults are not significantly cooled by the injected CO2. Meanwhile, the thermal impact at the injector well indicates that fractures will initiate after several years of injection but will not propagate as the injection pressure does not exceed the minimum reservoir fracture propagation pressure. The inclusion of thermal modelling in coupled geomechanics-dynamic-thermal workflow presents an important step in ensuring the overall geomechanical containment risks for any CO2 sequestration project. The effects of cooling due to the thermal difference between the injected CO2 and the targeted formation can lead to significant thermal stresses which may induce changes in effective stresses and subsequently hydraulic fracture initiation and propagation. Therefore, understanding the mechanisms of reservoir and caprock failure under cooling conditions is crucial in developing safe and effective CO2 storage strategies.