Effect of pressure on methane recovery from natural gas hydrates by methane-carbon dioxide replacement

Methane recovery from natural gas hydrates via CH4-CO2 replacement is promising for its advantage in methane recovery and CO2 capture in the form of CO2 hydrates. However, up to date, it is still unclear what influence the CH4-CO2 replacement rate and CH4 recovery efficiency. In this work, the effects of the pressure on the dynamic of the replacement are systematically investigated by in situ Raman. The results indicate the CH4-CO2 replacement rate and CH4 recovery efficiency are related to the total operating pressure and the CH4 partial pressure in a CH4-CO2 binary system. On the one hand, the CH4-CO2 replacement can only occur under such operating pressures that the CH4 partial pressure is lower than the pure CH4 hydrate formation equilibrium pressure and the CO2 partial pressure is higher than the pure CO2 hydrate formation equilibrium pressure. On the other hand, under a certain pressure, the lower CH4 partial pressure leads to the higher replacement rate. Due to that the condition of temperature and pressure changes continuously in the process of the replacement, the research results are of significance for guiding the successful CH4-CO2 replacement.