Intermittent CO2 injection for methane production and carbon sequestration in natural gas hydrate reservoirs

The CO2 injection-assisted depressurization method addresses the dual goals of methane hydrate extraction and carbon sequestration. A coupled THMC model was developed to investigate methane recovery and CO2 sequestration in the Shenhu Area of the South China Sea. Molecular dynamics simulations were conducted to study the impact of pressure variations on hydrate decomposition, elucidating the mechanisms of different injection strategies. Sensitivity analyses using experiment design and response surface methodology identified optimal parameters for safe and efficient hydrate extraction and carbon sequestration. The results show that starting CO2 injection into adjacent wells after 0.5 years enhances production while minimizing formation subsidence. Both reservoir modeling and molecular simulations confirm that the dual-well intermittent CO2 injection combined with depressurization achieves efficient hydrate extraction and substantial CO2 storage. Injection temperature was identified as the most sensitive parameter, followed by the interaction of soaking time and injection temperature, soaking time alone, and injection pressure. Optimized parameters include an 11-day soaking time, 20 MPa injection pressure, and 20 °C injection temperature. This study provides theoretical guidance for advancing natural gas hydrate development and improving CO2 geological storage strategies.