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A substantial fraction of methane in undisturbed coal beds is present in the condensed latent state, so that methane evolution from coal may be not always quantitatively predicted reliably. On the basis of experimental data, an equation expressing the amount of gas hydrate through the sorption capacity and actual humidity of coal is obtained. Analysis showed that the gradient of gas pressure in the marginal zone of a coal bed is linearly dependent on the saturation of the pore space with the hydrate. The high gradient of gas pressure and high gas content of coal beds along with local disruption of coal and re-distribution of rock pressure are the major factors causing instantaneous outbursts of coal and gas.

Abstract. This paper deals with the development and analysis of the method of predicting gas-dynamic phenomena due to the gas hydrates in coal seams. With the help of the method of mathematical modelling the rate of dissociation of gas hydrates depending on the size of particles was determined as well as the correlation between the speed of moving the boundary line of the dissociation of gas hydrates in the pore space of coal and that of extending of the wave of crushing. The regularity of gas pressure distribution in a coal seam marginal zone after dissociation of gas hydrate depending on its saturation capacity and taking into account the changing coefficient of permeability of this zone was stated. It was also found that this kind of gas-dynamic processes in the presence of gas hydrates in the pore space of coals depends on critical value of permeability of a coal seam marginal zone.

The possibility of gas hydrate formation in porous space of coal has been studied. The experiments conducted have proven the possibility of methane gas hydrate formation in moist coal. It has been demonstrated that the decomposition points of methane gas hydrates in coal are near to the phase equilibrium curve for bulk methane hydrate. Only part of water absorbed by coal can be involved in the methane gas hydrate formation. With the increase in gas pressure increases the amount of gas hydrate formed in natural coal. For formation of hydrates at a positive temperature, the pressure in the system has to be at least 2 MPa. At the same time the speed of formation and decomposition of gas hydrates in coal is big enough.

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