Methane recovery from natural gas hydrate in porous sediment using pressurized liquid CO2

Abstract The dynamics of CH 4 replacement in natural gas hydrate with liquid CO 2 was studied with a high pressure three-dimensional reactor. Five groups of hydrate samples were formed to investigate the effect of hydrate reservoir properties on CH 4 –CO 2 replacement reaction. The results showed that CH 4 in the hydrate gradually moves to the liquid CO 2 phase while CO 2 in the liquid phase penetrates into the hydrate under pressure–temperature conditions not only within the phase zone surrounded by ( L CO 2 – V CO 2 ) , ( water – H CO 2 – L CO 2 ) , and ( water – H CH 4 – V CH 4 ) curves but also that above ( L CO 2 – V CO 2 ) and ( water – H CH 4 – V CH 4 ) curves. The replacement rate and amount of CH 4 increase with the increase of hydrate saturation in the sediments. Compared with injecting gaseous CO 2 method, liquid CO 2 injection is also benefit for the recovery of CH 4 from hydrate reservoir with much free water or that without underlying gas room to the extent that the injection of liquid CO 2 is kept by high gas saturation. The replacement percent of CH 4 hydrate decreases with the increase of hydrate saturation, but increases with the increase of water saturation. A higher replacement percent is obtained in the zone surrounded by three phase curves of ( L CO 2 – V CO 2 ) , ( water – H CO 2 – L CO 2 ) and ( water – H CH 4 – V CH 4 ) .