A novel method to enhance methane hydrate exploitation efficiency via forming impermeable overlying CO2 hydrate cap

To enhance the exploitation efficiency of natural gas hydrate by decreasing the yield of water, a novel “reservoir reformation” concept is proposed that involves the reformation of a natural gas hydrate reservoir by constructing an artificial impermeable overlying CO 2 hydrate cap. The feasibility of this concept has been demonstrated in this laboratory-scale experiment. After reformation by injecting CO 2 emulsion into the permeable overburden, a confined environment with an impermeable CO 2 hydrate cap is successfully constructed for depressurization operation. The cap can maintain mechanical stability until the end of production process. With the protection provided by the artificial CO 2 hydrate cap, the production efficiency was greatly improved to 83.3% and the water yield is remarkably decreased. Moreover, the optimal CO 2 /H 2 O volume ratio of the emulsion for forming the desired CO 2 hydrate cap was confirmed to be 1:1. The formation of CO 2 hydrate cap can also protect the geological stability of depleted methane hydrate zones and seal a large amount of CO 2 , which is of both energetic and environmental significance; however, intensive and extensive research should be conducted in the future.