Research of hydrate and ice formation in soils during cyclic fluctuations of temperature

Peculiarities of phase transitions water-gas hydrate and water-ice in dispersed methane-saturated sediments during cyclic heating and cooling are investigated on the base of experimental simulation. Experimental data on hydrate and ice formation conditions in pore space of the sediments are obtained. It is noted, that only a part of free pore water is converted into hydrate during cooling of sediment, remaining water is converted into ice during freezing. Hydrate formation conditions in the sediments studied were different from the conditions in the system "pure water-methane gas" and were shifted into thermodynamic field of lower temperatures and higher pressures. The influence of sediment grain size and number of cooling-heating cycles on P/T conditions of hydrate formation is studied experimentally. Petrographic structure of the sediments saturated by methane hydrate is discussed.