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. CO2 replacement of NGH is widely of interest because it can realize hydrate exploitation and carbon dioxide capture at the same time, and CO2 replacment of CH4 in NGH can stabilize the formation. However, the disadvantages of CO2 replacement of NGH are low recovery efficiency and slow replacement rate. This review summarizes all of the developed enhanced methods and technologies of CO2 replacement in recent years and compares the CH4 recovery efficiency of these methods and discusses the main influencing factors of these methods. These methods include liquid CO2 (emulsion CO2) replacement, CO2/N-2 replacement, CO2/H-2 replacement, CO2 replacement combined depressurization, and CO2 replacement combined thermal stimulation. In general, using a gas mixture for replacement could obtained high CH4 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 CH4 recovery significantly, but energy consumption also needs to be considered.

Automated summary

CO2 replacement of NGH is crucial in energy development, and while it faces challenges of low recovery efficiency and slow replacement rates, coupling with depressurization or thermal stimulation can significantly enhance CH4 recovery.