Evidence of liquid water formation during methane hydrates dissociation below the ice point

Stability and growth of gas hydrates below the ice–hydrate–gas equilibrium line on the P–T phase diagram

“…The three-phase ice-hydrate-gas equilibrium line, as calculated from CSMGem , and the calculated line of the supercooled water-hydrate-gas metastable equilibrium (Istomin et al, 2006) are shown in the diagram. Formation of supercooled water upon methane hydrate dissociation in the temperature range between 253 and 273 K was confirmed by the experiments (Melnikov et al, 2009). The following empirical equation was obtained for the pressure at which methane hydrate dissociated into supercooled water and gas:…”

“…1) and the procedure are given elsewhere (Mel'nikov et al, 2007;Melnikov et al, 2009). Briefly, the main element of the experimental setup was a high-pressure reactor.…”

“…Makogon (1961Makogon ( , 1981 proposed that, below the ice melting point, hydrates dissociated in accordance with the scheme of hydrate-liquid water-ice +gas. Clear experimental evidence that dissociation of small hydrate grains at temperatures below 273 K can proceed in two stages with formation of supercooled water and its crystallization was presented by Mel'nikov et al (2007) and Melnikov et al (2009). The formation of supercooled water was visually observed during the dissociation of propane hydrates (Mel'nikov et al, 2007) and methane hydrates (Melnikov et al, 2009) metastable state (the induction time of ice nucleation) depended on the hydrate dissociation temperature and ranged from tens of hours at 270 K to a few seconds at 253 K.…”

Morphological and Compositional Characterization of Self‐Preserved Gas Hydrates by Low‐Vacuum Scanning Electron Microscopy

“…longer induction time for nucleation), resulting in a weaker preservation effect as suggested by Melnikov and coworkers. [23] Herein, we demonstrate that LVSEM is a powerful tool not only for morphological observations on uncoated hydrate and ice samples without alteration, but also for investigating microstructural distributions of the two phases using compositional contrast. Both the as-grown Ar and Kr hydrates were observed to be dense materials with dimpled surface topology.…”

“…[22,23] Assuming the presence of such a super-cooled liquid water phase, it might cover (wet) surfaces of decomposing hydrates, and some hydrate crystals might be captured in the water medium during crystallization.…”