A screening tool for carbon dioxide injection in gas reservoirs based on the material balance approach

Significant efforts are made to reduce the carbon dioxide concentrations in the atmosphere as part of a global scheme that aims to mitigate climate change. Carbon geological storage involves the storage of CO₂ permanently in a subsurface reservoir, commonly a brine saturated aquifer, or a depleted reservoir. Carbon dioxide is also injected for enhanced oil or gas recovery (EOR/EGR). This work applies a material balance to CO₂ for injection and storage in a single-phase dry and/or condensate gas reservoirs. The developed framework based on piston-like displacement can be either used for pressurising depleted gas reservoirs with CO₂ or for EGR. Sensitivity studies of carbon dioxide injection in pressure depleted gas reservoirs and piston-like injection under water drive are presented for various production rates and initial reservoir pressures. Monte Carlo simulations are conducted for combinations of porosity and permeability of different formations such as sandstone, shale, and unconsolidated sand. The results show that CO₂ piston-like injection in EGR is more efficient compared to first depleting the reservoir and then injecting CO₂ as it controls the water influx. The recovery factors in CO₂ EGR are almost insensitive to initial pressures and production rates for both single-phase and condensate gas. Higher permeability formations are much more effective, however, a formation with very high permeability may lead to stability problems.