On the theory of the decomposition of a metastable gas hydrate

Methane hydrate decomposition at atmospheric pressure in the overheated state relative to the equilibrium temperature (TS = 193 K) at positive (T0 > 273 K) and negative (T0 < 273 K) temperatures is discussed with reference to available experimental data. Two temperature ranges (193 K < T0 < 240 K and 240 K ≤ T0 < 273 K) arte distinguished at negative temperatures, and one temperature range (T0 > 273 K) at positive temperatures. For the lower range of negative temperatures, it is accepted in the construction of the theoretical model that the major factors determining the intensity of gas hydrate decomposition into ice and gas are Arrhenius-type kinetics and conductive heat transfer. Two schemes, namely, frontal and bulk ones are considered. For the upper range of negative temperatures, where an anomalous preservation effect is observed in experiments, it is assumed in the theoretical model that the release of the gas from the hydrate is controlled by the diffusion mechanism of gas transport through the solid phase or through the surface ice crust. For the positive temperatures, it is accepted that the decomposition rate is determined by the heat flux through the draining water film that has resulted from hydrate decomposition. Calculations have been carried out for different initial and boundary temperatures, and the results of the calculations have been analyzed and have been compared to available experimental data.