Integrating CO2 sequestration and enhanced gas recovery: a comprehensive evaluation for sustainable carbon management

Greenhouse gases pose a significant threat to life on Earth by trapping infrared radiation, leading to global warming. In Bangladesh, carbon dioxide (CO2) emissions have surged by 40% from 2000 to 2020, primarily from the power industry and process sector, making CO2 the most significant contributor to the country's greenhouse gas inventory. One promising mitigation strategy is the integration of CO2 sequestration with enhanced gas recovery (CO2-EGR-CCUS) in depleted gas reservoirs. This study presents a reservoir simulation-based investigation using CMG software to evaluate the dual objective of maximizing CO2 storage and recovering residual methane. A comprehensive sensitivity analysis was also performed to assess the impact of well placement, injection rate, and injection pressure on CO2 injectivity and methane recovery. Among the tested scenarios, staggered well placement with an injection rate of 47 MMSCF/D at 4700 psi yielded the highest gas recovery factor of 4.52%, recovering 1.3 BCF of methane from a depleted gas reservoir with a Gas Initially in Place of 28.8 BCF. The abandoned gas rate was 0.1 × 10⁶ SCF/day, and residual gas saturation was 0.1. The cumulative CO2 injection reached 3.82 × 1012 SCF, with 1.36 × 1012 SCF securely stored under a fracture pressure limit of 6000 psi, as determined using the Pennebaker Correlation. Notably, the project demonstrates a CO2 capture potential equivalent to 1.24% of Bangladesh’s total annual CO2 emissions. Staggered well placement also achieved the highest sweep efficiency (12.27%), outperforming linear and five-spot patterns by 3.19% and 2.41%, respectively. These findings highlight the feasibility of combining CO2 storage with enhanced methane recovery as a scalable and sustainable strategy for carbon management in Bangladesh. The study contributes valuable insights into optimizing CCUS operations under site-specific geological and operational constraints.