A Review on Research on Replacement of CH₄ in Natural Gas Hydrates by Use of CO₂

This paper introduces the research advances on replacement of CH₄ in Natural Gas Hydrates (NGHs) by use of CO₂ and discusses the advantages and disadvantages of the method on the natural gas production from such hydrates. Firstly, the feasibility of replacement is proven from the points of view of kinetics and thermodynamics, and confirmed by experiments. Then, the latest progress in CH₄ replacement experiments with gaseous CO₂, liquid CO₂ and CO₂ emulsion are presented Moreover, the superiority of CO₂ emulsion for replacement of CH₄ is emphasized. The latest experiment progress on preparation of CO₂ emulsions are introduced. Finally, the advancements in simulation research on replacement is introduced, and the deficiencies of the simulations are pointed. The factors influencing on the replacement with different forms of CO₂ are analyzed and the optimum conditions for the replacement of CH₄in hydrated with different forms of CO₂ is suggested.