Conversion of depleted gas reservoirs into underground CO2 storage. =

One of the most important problems facing the environment nowadays is climate change. CCS (carbon capture and storage) has been considered a promising mitigation technology that can help in reaching the decarbonization goal and contribute to the climate change mitigating efforts. After presenting an overview of the CCS technology, the various storage types and the importance of the trapping mechanisms, numerical simulations and models will be investigated to understand the major effect of the reservoir and injection parameters on the injection process of CO2. A detailed sensitivity analysis was performed, investigating some key factors to determine their impact on the storage capacity as well as on the injectivity. These factors included depth and size of the reservoir, dimension of the surrounding aquifer, petrophysical properties, and injectivity parameters. The findings were compared and discussed to provide insights into the storage capacity of CO2 into various geological formations characterized by different parameters and the injectivity based on different injection strategies. The results show that the structural trapping is the dominant mechanism in all sensitivities, the mineral trapping is strongly affected by depth variation, residual trapping potential strongly regulated by the percentage of residual gas, moreover, the solubility trapping changes significantly with the irreducible water saturation as well as with the aquifer size. Permeability and porosity both play an important role in the dissipation of the pressure in the reservoir. Furthermore, injection rates have a direct correlation with the injectivity in the reservoir as well as the ramp up injection strategy offer a good control of the well-bottom hole maximum delta pressure with the increase in the ramp-up steps.