Techno-Economic Investigation of CO2 Injection Schemes for Geological Carbon Storage in Saline Aquifers

Deep saline aquifers are among the most promising formations for large-scale carbon capture and storage (CCS); however, reservoir pressure buildup, limited CO2 dissolution, plume migration, and salt precipitation can reduce storage efficiency and injectivity. This study evaluates the technical and economic performance of engineered CO2 injection strategies, including intermittent CO2 injection (ICI), water-alternating-CO2 (WA–CO2), carbonated water injection (CWI), and carbonated water-alternating-CO2 (CWA–CO2), under low- (180 mD) and high-permeability (1000 mD) saline aquifers and injection rates ranging from 0.01 to 0.5 MTPA. Laboratory-derived relative permeability and CO2 diffusivity data were incorporated into three-dimensional compositional reservoir simulations, while the most promising strategy was validated using the Sleipner benchmark model. Techno-economic performance was assessed through Monte Carlo uncertainty and sensitivity analyses. The results show that injection strategy, rate, and reservoir permeability strongly influence trapping efficiency and pressure evolution. ICI increased dissolution trapping by up to 20%, enhanced residual trapping by approximately 40%, and reduced average reservoir pressure by up to 10%, although its extended operating period reduced its economic attractiveness. Among the evaluated alternatives, WA–CO2 provided the best balance between technical and economic performance by enhancing dissolution trapping, improving pressure management and plume control, and maintaining storage costs within 3.6–3.7% of the continuous injection base case. Field-scale validation using the Sleipner model demonstrated improved long-term trapping efficiency and reduced mobile CO2 and plume extent. Monte Carlo analysis (20,000 realizations) confirmed the economic robustness of the evaluated strategies under the assumed policy framework, identifying Section 45Q tax credit and discount rate as the dominant economic drivers. These findings demonstrate that properly designed WA–CO2 schemes can significantly improve the technical and economic performance of geological CO2 storage.