Effectiveness of CO2-N2 injection for synergistic CH4 recovery and CO2 sequestration at marine gas hydrates condition

Abstract CH4 hydrate have been considered as the future clean energy resource. Recovery of CH4 from natural gas hydrates by CO2 replacement is a promising method for energy harvest and CO2 sequestration. Field production tests have proved the feasibility of gas production by CO2 replacement in the permafrost region. However, most of the hydrate reservoirs are located at marine conditions where pressure and temperature conditions are not favorable for the replacement process. In this work, we identified a possible marine condition, where mixed hydrates could potentially form. We investigated the technical feasibility of CH4 recovery by a depressurization process followed by the injection of CO2-N2 gas. To quantify the dynamic behavior of mixed hydrates formation and dissociation, we developed a numerical method to estimate the phase partitioning during the replacement process. The effects of mixed gas compositions in the reactor on the replacement efficiency were investigated. Our experimental results showed that rapid co-growth of mixed hydrates occurs when the injected gas composed of a lower N2 concentration (