Dissociation and Self-Preservation of Gas Hydrates in Permafrost

• Published in: Geosciences (Basel) 2018-12, Vol.8 (12), p.431
• Main Authors: Chuvilin, Evgeny, Bukhanov, Boris, Davletshina, Dinara, Grebenkin, Sergey, Istomin, Vladimir
• Format: Article
• Language: English
• Subjects: Dissociation; Earth science; Equilibrium; Experiments; Frozen ground; gas hydrate; Gas hydrates; Gas pressure; Gases; Hydrates; Ice; Kinetics; Methane; Methane hydrates; Moisture content; Permafrost; Phase equilibria; Physical properties; Porous materials; Preservation; Pressure drop; Salinity; Salinity effects; Sediments; self-preservation; Soil; Survival; temperature
• ISSN: 2076-3263; 2076-3263
• DOI: 10.3390/geosciences8120431

Gases releasing from shallow permafrost above 150 m may contain methane produced by the dissociation of pore metastable gas hydrates, which can exist in permafrost due to self-preservation. In this study, special experiments were conducted to study the self-preservation kinetics. For this, sandy samples from gas-bearing permafrost horizons in West Siberia were first saturated with methane hydrate and frozen and then exposed to gas pressure drop below the triple-phase equilibrium in the “gas–gas hydrate–ice” system. The experimental results showed that methane hydrate could survive for a long time in frozen soils at temperatures of −5 to −7 °C at below-equilibrium pressures, thus evidencing the self-preservation effect. The self-preservation of gas hydrates in permafrost depends on its temperature, salinity, ice content, and gas pressure. Prolonged preservation of metastable relict hydrates is possible in ice-rich sandy permafrost at −4 to −5 °C or colder, with a salinity of