Experimental Study of Conditions for Methane Hydrate Productivity by the CO2 Swap Method

Various saturated methane hydrates (MHs) formed in porous media were swapped with CO2 to investigate the principles of replacement reactions in different regions surrounded by three curves: (L-V)CO2, (H-V)CH4, and (H-V)CO2. The replacement percentage was analyzed to evaluate the productivity of MHs, with the replacement reactions in zone A [above (H-V)CO2, above (H-V)CH4, and above (L-V)CO2], zone B [above (H-V)CO2, above (H-V)CH4, and below (L-V)CO2], and zone C [above (H-V)CO2 below (H-V)CH4, and below (L-V)CO2]. Temperature conditions under the ice point caused restrictions in the replacement process. The two key factors affecting this phenomenon are the area of MHs for the replacement reactions and the diffusibility of CO2 in the three zones. Pressure signals of replacement procedures in the three zones were discussed to investigate the possible:CO2-CH4 exchange kinetics. Two replacement stages were Observed: surface replacement and inner layer replacement. Pressures in zone C decreased instead of recovering to the equilibrium line of the MHs. We also analyzed other affecting factors, such as-the pressure and temperature. In zone C, replacement percentage decreased as the pressure increased at the same replacement temperature and MH saturation. In zone B, replacement percentage increased as the temperature increased with the same pressure and MH saturation, although this tendency Was not obvious when the temperature was below the freezing point.