Integrated CO2 storage and geothermal energy recovery in a heterogeneous shallow marine sandstone reservoir

CO 2 plume geothermal systems are attractive for depleted hydrocarbon reservoirs; however, their performance has commonly been evaluated under simplified assumptions that neglect geological heterogeneity. This limitation is especially critical in shallow marine sandstones, where strong spatial variability in porosity and permeability governs CO 2 storage and thermal energy extraction. This study investigates coupled CO 2 storage and geothermal energy recovery in heterogeneous shallow marine sandstone reservoirs using the Lower Gharif Formation as a representative case. A three-dimensional geological model was constructed from well-log and core data in Petrel and simulated in the CMG-STARS. Long-term simulations spanning 30 years were conducted, including an initial CO 2 injection phase followed by circulation under two well-configuration scenarios: a baseline five-spot layout and an adjusted five-spot layout. Within the modelled geological realization and operational assumptions, the results show that reservoir heterogeneity strongly influences plume migration, injectivity, bottom-hole pressure behavior, and thermal response. High-permeability zones promote rapid CO 2 advance and earlier cooling at some producers, whereas lower-permeability zones delay plume arrival and provide greater opportunity for heat exchange before producer arrival. These lower-permeability zones also generate greater flow resistance and higher simulated bottom-hole pressures, indicating the need for geomechanical assessment when defining field operating limits. Under the modelled realization, the baseline equal-spacing and adjusted-spacing scenarios produced different thermal responses, with the performance-guided adjusted layout increasing average BHT and cumulative extracted thermal energy relative to Sc1. The reduction in total CO 2 production after well rearrangement was accompanied by an increase in bottom-hole temperature, showing that a higher produced CO 2 temperature can compensate for the reduction in produced CO 2 volume in terms of overall geothermal energy production.