Formation of pore CO2 hydrates in permafrost: evidence from laboratory modelling

Sequestration of carbon dioxide (CO2) in gas hydrate and its disposal in shallow sediments under hydrate stability conditions is an efficient way of reducing carbon dioxide emission to the atmosphere. Laboratory modelling of carbon dioxide hydrate formation in freezing and frozen sand demonstrates that sediments within and below permafrost are potentially suitable reservoirs in this respect. The experiments are conducted in high-pressure cells with automatic pressure and temperature monitoring during hydrate formation in ice-bearing sand samples saturated with carbon dioxide at constant negative temperatures of −1°C to −8°С. The work includes testing the sensitivity of pore carbon dioxide formation to temperature, cyclic freezing/thawing, and initial ice saturation. According to experimental evidence, pore carbon dioxide hydrate can form in a large range of negative temperatures, while pore moisture can be liquid or solid. Hydrate formation accelerates when the samples are exposed to cyclic freezing and thawing. The formation of carbon dioxide hydrate is most active in the 45%–65% range of initial ice saturation. The results have implications for possible patterns of carbon dioxide hydrate formation in permafrost by injection of carbon dioxide into the zone of hydrate stability and for respective permafrost responses.