The Affect About Pore Characteristics Of Coal To The Coal-bed Methane Desorption

China has many high-gas coal mine, coal-bed methane reserves are abundant, but because of the complexity of geological conditions, the imperfections of technical and theoretical basis, lead to the low recovery ratio of China's coal-bed methane and it difficult to achieve industrial exploitation. To improve the efficiency of extraction of coal-bed methane, we must study the various coal reservoirs and the properties of the coal-bed methane in the exploration and development area.Research samples collected from the active areas and the development areas of the methane exploration in our country, taking into account the country's coal rank. Have experiments of the samples coal: proximate analysis, maceral identification, porosity determination, scanning electron microscopy experiments, mercury intrusion experiment, nitrogen adsorption and desorption isotherm experiment, synthesis various conclusions to reveal the pores of coal characteristics and desorption, in order to lay the foundation for the coal-bed methane extraction.Coal is a non-uniform pore distribution, porosity of coal of different species are different and porosity of coal in different area with the same kind are also different. The larger the surface area of coal pores, the greater the pore volume. As the coal rank, maceral various, specific surface area and pore structure are very different. The more micro-pores eixst, the larger pore volume have, and the more favorable adsorption to coal-bed methane. The higher the rank of coal, the more residual value will be.When the pressure down to 0.5～1Mpa, the desorption rate of methane increase in the maximum, nearly straight line pattern. High rank of the coal bed methane reservoir, when the pressure reduce to 2～10MPa, coal-bed methane desorption rate was not increased significantly; when the pressure reduce to 0.5～2MPa , the rapid increase in coalbed methane desorption. The low rank coal-bed methane reservoirs, coal-bed methane desorption rate increase showing different rate, and only the largest increase in the low-pressure stage. Depressor coal-bed methane mining practice, we must protect the continued stability of the pressure drop, if pressure drop too much would hurt the coal and affect the properties of the reservoir; if pressure drop too little, not conducive to the methane desorption. Pore characteristics of coal will affect the desorption rate of coal-bed methane , under the conditions that the coal with the same composition and coal rank, in the isothermal desorption of low-voltage section, if the pore structure uniform and the pore throat distribution is concentrated, the coal-bed methane desorption rate is high. The micropores holes and small holes are mainly affectting the volume of coal-bed methane desorption and its desorption rate. The coal reservoir micropores closed weaker, the higher the pressure differential transmission efficiency, then the gas adsorbed on the inner micropores surface are more desorption volume and higher desorption efficiency.The affect about pore characteristics of coal to the Coal-bed Methane desorption, are the pore size and its proportion of the distribution , the pore throat distribution, and pore shape type, which combined three factors affect.In the coal-bed methane desorption process, the pressure drop control is closely related with the pore structure and pore types.