Kinetics of phase transitions in ice- and hydrate-bearing sediments under thermal impact

Recent global warming trends are degrading Arctic permafrost, posing risks to the construction of facilities and leading to increased emission of greenhouse gases. Methane emitted from thawing permafrost may be released by dissociation of intrapermafrost gas hydrates. Northern West Siberian permafrost contains two hydrate-bearing layers: the present zone of gas hydrate stability below 200 m depth and a shallow metastable hydrate zone (150–200 m) preserved from past geological conditions due to the self-preservation effect. Original laboratory tests on the kinetics of phase transitions revealed considerable differences in thermal responses of hydrate-bearing sediments under different pressures and temperatures close to in situ permafrost conditions. According to the experimental results, stable pore gas hydrates are resistant to warming and dissociate only within the range of positive temperatures determined by the equilibrium gas pressure. On the contrary, metastable pore gas hydrates are highly sensitive to thermal effects and prone to rapid dissociation, as they dissociate at some critical temperatures ∼1.0°С–1.5°С below the thawing point for non-saline sand. In this respect, the geotechnical and environmental risks associated with gas production from high-latitude West Siberian reservoirs can be reduced by incorporating the empirical temperature of pore gas hydrate dissociation into the design, in addition to the permafrost thawing temperature.