As the global energy demand rises, concerns regarding the increasing carbon levels deepen. Pushing the international community to pour their time and resources into exploring all avenues that bear potential to aid the decarbonization efforts. The decarbonization efforts attempt to either reduce carbon dioxide emissions or to capture carbon dioxide from the atmosphere. The oil and gas industry’s role falls into the first category. Where captured CO₂ is sequestered into geological stable formations as part of carbon capture, utilization, and storage (CCUS) or carbon capture and storage (CCS) projects. CCUS and CCS technologies hold the keys to decarbonization, possessing a large capacity capable of storing over 8000 GtCO₂, utilizing oil and gas reservoirs, saline aquifers, and coal beds to discard CO₂. In addition, the sequestration in geological structures is long-term, with minimal risk of reintroducing the stored gas back to the surface. This work investigates two scenarios, one in which the reservoir undergoes a tertiary production and another where the reservoir has reached the abandonment stage of its life cycle. The analyses are carried out by employing a historically matched numerical model of a real carbonate reservoir to explore CO₂ storage implications on the reservoir’s performance (EOR) and the efficiency of the injected gas storage in the subsurface. For a holistic evaluation, the numerical model accounts for relative permeability hysteresis, phase trapping, geochemistry, and thermodynamics. Various analyses are conducted to establish the recommended gas blend injected, the importance of miscibility, and the manner of injection (WAG or gas flood). The results showcased how miscible injection outperforms immiscible in CO₂-EOR and sequestration efficiency. Furthermore, gas flood is recommended over WAG, especially when recycling produced gases is possible to store larger volumes of carbon dioxide.