Technological research progress on CO₂-CH₄ replacement for hydrate exploitation and enhancement

Considering the huge reserve and wide distribution in nature, natural gas hydrates have a great potential to become an alternative energy resource in future. How to economically and safely recovery natural gas from hydrate reservoirs is the focus of current researches. The method by using carbon dioxide (CO₂) to replace methane (CH₄) within natural gas hydrates has drawn enormous interests due to its two-fold bonus: CH₄ recovery for energy and CO₂ sequestration for safety. The latest experimental and numerical research in technology on CO₂-CH₄ replacement for hydrate exploitation, and the feasibility as well as its challenges were summarized. For the challenges to the low efficiency and slow rate in the replacement process, various methods and technologies to enhance the replacement processes were analyzed on examples of the usage of different phase CO₂, cooperation with small-molecule gas, and combination with other exploitation methods. Finally, technical barriers and application limitations of different enhancement technologies were pointed out, and the research direction and development prospect of CO₂-CH₄ replacement for hydrate exploitation were prospected.