Formation of supercooled water upon dissociation of propane hydrates at T < 270 K

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

“…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.…”

“…The occurrence of metastable propane hydrates was observed within the thermobaric area bounded by the ice-propane hydrate-gas equilibrium line, the line of the supercooled waterpropane hydrate-gas metastable equilibrium and the isotherm T=263 K. The formation of supercooled water during dissociation of propane hydrates was reliably recorded in the range between 263 and 273 K. The following empirical equation was obtained for the pressure at which propane hydrate dissociated into supercooled water and gas (the supercooled water-propane hydrategas metastable equilibrium line) (Mel'nikov et al, 2007):…”

“…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.…”

Plasmoid Phenomenon of

“…These anomalies are detected in the appearance of two waves with the same polarization and close wave numbers. For Baikal basin in sediments of which methane hydrates are developed, at the degassing process their dissociation into liquid (supercooled) water and gas takes place as it is shown in the experiments [60]. This mechanism may case a plasmoids formation.…”

Study of gas hydrate metastability and its decay for hydrate samples containing unreacted supercooled liquid water below the ice melting point using pulse NMR

“…For the first time, reliable experimental evidence on gas hydrate dissociation into supercooled water and gas below the ice melting point as well as pressure-temperature (p-Т) data on the supercooled water-hydrate-gas (L sw -H-G) metastable equilibrium were obtained for propane hydrate (Mel'nikov et al, 2003(Mel'nikov et al, , 2007. Subsequently, the possibility of hydrate dissociation into supercooled water and gas was confirmed for the hydrates of methane, ethane, carbon dioxide, and Freon-12 (CCl 2 F 2 ) using optical microscopy observations (Melnikov et al, 2009(Melnikov et al, , 2010(Melnikov et al, , 2011, Raman (Ohno et al, 2011) and pulsed NMR (Melnikov et al, 2012 spectroscopy, and differential thermal analysis (DTA) Melnikov et al, 2015).…”