Status and perspectives of the hydrate technology for carbon sequestration in permafrost region: A review

Carbon dioxide (CO2) sequestration in ocean or permafrost regions based on hydrate technology is one of the most promising carbon-negative technologies. Especially, direct CO2 hydrate storage in permafrost regions, which has the most potential for long-term sequestration, maximally decreases the sequestration leaking threats. Therefore, in this paper, we provide a complete summary of the feasibility, potential and site selection of CO2 hydrate sequestration in permafrost regions. In particular, we detailedly summarized the natural evidence of the gas hydrates long-term and stable existence in permafrost and near-polar regions over the past 60 years. Furthermore, the CO2 hydrate crystal structure, thermodynamic and kinetic phase transfer properties under permafrost conditions are introduced from mechanism and modeling perspectives. Additionally, the applicability of conventional geological carbon sequestration techniques and transferability of hydrate extraction cases in permafrost environments is analyzed from an engineering application perspective. Based on the huge CO2 hydrate storage potential in permafrost region, the carbon storage site selection guidelines are explained, with China as an example. The factors such as the area of the permafrost regions, depth, continuity and stability of the permafrost layer, permafrost geomechanics and industrial support capabilities are analyzed in detail. In contrast, the Mohe region in the Great Xing'an Mountains is considered the most promising storage site. Finally, we emphasize the importance of ecological impacts of carbon sequestration in permafrost regions and describe the directions for future research.