Review on Enhanced Technology of Natural Gas Hydrate Recovery by Carbon Dioxide Replacement

Natural gas hydrate (NGH) is one of the most potential alternative energy sources in the future due to its huge reserves. Economic, efficient, and safe exploitation of hydrate reservoirs is key to the utilization of NGH. CO 2 replacement of NGH is widely of interest because it can realize hydrate exploitation and carbon dioxide capture at the same time, and CO 2 replacment of CH 4 in NGH can stabilize the formation. However, the disadvantages of CO 2 replacement of NGH are low recovery efficiency and slow replacement rate. This review summarizes all of the developed enhanced methods and technologies of CO 2 replacement in recent years and compares the CH 4 recovery efficiency of these methods and discusses the main influencing factors of these methods. These methods include liquid CO 2 (emulsion CO 2 ) replacement, CO 2 /N 2 replacement, CO 2 /H 2 replacement, CO 2 replacement combined depressurization, and CO 2 replacement combined thermal stimulation. In general, using a gas mixture for replacement could obtained high CH 4 recovery. The appropriate concentration of a displacement mixture gas can avoid the increase of energy consumption in production gas separation. Replacement coupling depressurization or thermal stimulation enhanced the CH 4 recovery significantly, but energy consumption also needs to be considered.