Feasibility Assessment of Utilizing N2 with CO2 in Enhanced Gas Recovery and CO2 Sequestration

Abstract A significant number of carbon capture and storage (CCS) projects integrate CO2 sequestration with enhanced gas production (EGR). Integration of CCS and EGR provides a practical approach to maximize gas production while sustaining environmental goals. While numerous lab experiments explored mixing CO2 and N2 to increase gas recovery and reduce CO2 cost, this study examines the effects of N2-CO2 mixture on a field scale and explores the effects on CO2 storage capacity. To visualize the effects of the N2-CO2 mixture on gas recovery, 3-D simulation models were employed to compare utilizing the mixture in a conventional dry gas reservoir. For sensitivity analysis, numerous scenarios were considered, including injection rates and reservoir properties. The model entails a 10-year simulation period, with production starting 4 years before injection, stopping production once the concentration of CH4 falls to 0.5. Maximum injection pressure is set at 8,000 psi, avoiding potential CO2 leakage. This will help in mimicking field conditions to assess the maximum economic recovery and CO2 storage. While results found in the literature offer contradictory results, the results highlight the positive influence of N2 on gas production. Field-scale results showcase that combining N2 with CO2 could be effectively utilized as it yields an overall similar recovery to pure CO2. In fact, in lower permeability reservoirs, N2 provides higher gas recovery than that of CO2 by 2-3%. However, in higher permeability reservoirs, the results shift the other way, with CO2 outperforming N2. This result is mainly driven by the breakthrough of N2 and CO2, where in low permeability, CO2 breakthrough is faster than N2, while reversing the behavior in high permeabilities. Nonetheless, CO2 storage efficiency is the same in both cases, effectively storing more than 90% in both cases. The total amount of sequestered CO2 remains the highest when injecting CO2 as the initial volume of CO2. Therefore, this method can be a feasible option for improving project economics while maintaining the environmental objectives. Incorporating N2 with CO2 in EGR projects provides a novel approach to sequestering CO2 while generating the highest gas production and cost reduction. In addition to reducing processing costs, injection of N2-CO2 can reduce potential corrosion issues in production wells by minimizing CO2 production. Therefore, including N2 can facilitate the optimization of CCS and EGR projects.