Abstract:

 There are three stages for the production of coalbed methane: desorption, diffusion and osmosis. The diffusion process of methane and multicomponent gases in the deformed coals is not consistent with that in primary coals. The change of external pressure is only an external factor in the whole process of adsorptiondesorption in tectonically deformed coals; the essential factors of the process are the deformation, the change of structure and the adsorption potential. Those factors are the root causes which induce the irreversible process of desorption. When the balance of coal and multigas like CH4 has been destroyed, the tectonically deformed coals that deformed stronger shows a phenomenon of hysteresis of desorption after the pressure reduced, and the gas in weakly deformed coal will desorb quickly. The process of desorption has two phases: one is the gas desorption and the other is the process of free gas from micropores diffusing to the bigger pores; the latter one determines the gas diffusion rate. The gas diffusion mechanism of tectonically deformed coals was determined by pore shape, size, connectivity and the properties and condition of multigas. Ductile deformation coal has many micropores and its diffusion mode is the Knudsen diffusion. Brittle deformation coal has many bigger pores and the connectivity of pores is much better, so the diffusion mode is the Fick diffusion. The diffusion mode of brittleductile deformation coal is the transitional diffusion. The well test osmosis of brittle deformation coal is higher than that of ductile deformation coal and the well test osmosis of primary structure coal is the lowest. There are many mesopores in brittle deformation coal, and the others are micropores; submicropores and ultramicropores cannot be detected. The brittle deformation also can increase the connectivity of pores. Ductile deformation coal has a small amount of mesopores, and the amounts of micropores and submicropores increase fast; the process of diffusion and osmosis happened in mesopores and micropores, so the well test osmosis of ductile deformation coal was lower than that of brittle deformation coal.

Key words:  tectonically deformed coals, coalbed methane, desorption &, diffusion, osmosis