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

The dynamics of CH4 replacement in natural gas hydrate with liquid CO2 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 CH4–CO2 replacement reaction. The results showed that CH4 in the hydrate gradually moves to the liquid CO2 phase while CO2 in the liquid phase penetrates into the hydrate under pressure–temperature conditions not only within the phase zone surrounded by (LCO2–VCO2)(LCO2–VCO2), (water–HCO2–LCO2)(water–HCO2–LCO2), and (water–HCH4–VCH4)(water–HCH4–VCH4) curves but also that above (LCO2–VCO2)(LCO2–VCO2) and (water–HCH4–VCH4)(water–HCH4–VCH4) curves. The replacement rate and amount of CH4 increase with the increase of hydrate saturation in the sediments. Compared with injecting gaseous CO2 method, liquid CO2 injection is also benefit for the recovery of CH4 from hydrate reservoir with much free water or that without underlying gas room to the extent that the injection of liquid CO2 is kept by high gas saturation. The replacement percent of CH4 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 (LCO2–VCO2)(LCO2–VCO2), (water–HCO2–LCO2)(water–HCO2–LCO2) and (water–HCH4–VCH4)(water–HCH4–VCH4).

► Five 3-D hydrate samples are formed to study CH4–CO2 replacement with liquid CO2. ► Liquid CO2 adapts to hydrate reservoirs with/without underlying gas or free water. ► CH4 replacement rate and amount increase with the increase of hydrate saturation. ► Saturations of water and hydrate have different effect on CH4 replacement percent. ► There exists a phase zone that replacement rate and percent of CH4 are higher.