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

[Display omitted] • Feasibility of CH 4 recovery and CO 2 storage by gas injection at marine condition. • CH 4 hydrate co-growth and dissociation occurred depending on the gas composition. • High CO 2 composition is beneficial for co-growth of mixed hydrate. • Continuous CH 4 hydrate dissociation was observed with high N 2 composition. CH 4 hydrate have been considered as the future clean energy resource. Recovery of CH 4 from natural gas hydrates by CO 2 replacement is a promising method for energy harvest and CO 2 sequestration. Field production tests have proved the feasibility of gas production by CO 2 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 CH 4 recovery by a depressurization process followed by the injection of CO 2 -N 2 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 N 2 concentration (<25.2%). On the other hand, continuous CH 4 hydrate dissociation was observed when the injected gas was composed of a higher N 2 concentration (28.5%). During the prolonged replacement stage, the amount of CH 4 hydrate decreased and the amount of CO 2 -N 2 hydrates increased only slightly, which indicated that possible replacement occurred but at a very localized level. The results proved the technical feasibility of CH 4 production by gas injection at marine conditions, but the compositions of the mixture gas injected need to be well controlled. [ABSTRACT FROM AUTHOR]