Criticality of Incorporating Thermal Effects in CO2 Storage Development Evaluation of a High Porosity Depleted Carbonate Field

Abstract A comprehensive carbon dioxide (CO2) storage development plan study was conducted on Field X in offshore East Malaysia. The study is aimed at addressing, among others, geomechanical challenges and risks associated with CO2 injection and geological storage, injectivity and storage capacity. The thermal-induced containment risks include hydraulic fracture initiation and propagation in reservoir and caprock due to cooling by the injected CO2. Two-way coupled geomechanics-dynamic-thermal modelling workflow with rock properties degradation due to CO2-rock interaction and simultaneous history match for reservoir simulation and geomechanical subsidence prediction was implemented. Recognising the pore collapse behaviour of the reservoir, the Modified Cam Clay model was implemented in the geomechanical modelling with model parameters based on laboratory test data. The rock properties degradations were derived from triaxial tests conducted on untreated samples and samples dynamically aged with CO2 saturated brine, and the elastic and strength properties degradations ranged between 8 and 30%. Based on the coupled thermal geomechanical simulation, temperature cooling of up to 103 °C is localised within 2200 ft lateral distance from the injectors. The cooling resulted in fracture gradient reduction of up to 1400 psi in the reservoir and up to 700 psi in the caprock. The hydraulic fractures initiated will propagate in the reservoir but not in the caprock. The proposed CO2 injection scenario showed a low risk of shear and tensile failures in caprock, and all the faults remained stable. The mechanical properties degradation effects on fault stability, caprock integrity, reservoir expansion and seabed uplift are minimal. The subsidence predicted in the model before CO2 injection shows good match with Global Positioning System (GPS) measurement data over a period of 16 years. The output from the coupled geomechanical modelling was subsequently used to develop recommendations from geomechanical perspective which include CO2 injection pressure limit and its respective storage capacity together with measurement, monitoring and validation (MMV) programme using seabed and downhole monitoring as well as surface seismic methods and micro-seismic techniques.