Analysis Of Mining Rock Mechanics In Relieved Drainage Of Coal Bed Methane And Its Application

The rapid development of the national economics brings many mining industry problem, such as the shortage of coal resource, the worse of environment in coal area, the loose of coal bed methane, and so on, so the thought of simultaneous extraction of coal and gas is come into being. In this paper, aimed at the deposit condition of soft coal seam with high gas and low permeability, a synthetically study means combined with experimental study, theoretical analysis, numerical simulation, and physical modeling is applied to study the coupling mechanism of the seepage permeability of overlying coal rock, coal seam deformation and the gas migration, the mining-induced fractures development, the mining stress changing and the gas seepage law. The principle and method for pressure-relief mining of coal bed methane are put forward and applied to the practice successfully. The study results provide a theoretic reference for the simultaneous extraction of coal and gas. And the results with innovative significance are shown in the following:(1)Gas permeability test system designed by self are used to measure the gas permeability of broken rock samples, the relationship of the gas permeability and the depth of coal rock sample are presented to study the influence of the increasing or decreasing confining pressure on the gas permeability of broken rock samples.(2)Dynamic model of coal seam deformation and gas migration are established. This model considered the coupling mechanism of the coal seam deformation field, the stress field and the course of gas adsorption, desorption, diffusion and seepage in pore. The characteristic of Non-Darcy flow of the gas seepage in coal seams are studied. The Non-Darcy flowβfactor and the acceleration coefficient are introduced to reveal the objective essence of coal rock, coal seam deformation and the gas migration, the mining crack development, the mining stress changing and the gas seepage law.(3)Dynamic development of mining-induced fractures and the deformation rule of protected coal seam are analyzed under the influence of key strata by the comprehensive means of numerical simulation and physical modeling. The coupling analysis function of coal and rock damage and gas seepage in the software of the coupling system of flow and solid in rock failure process analysis( F-RFPA2D), is adopted to obtain the distribution characteristic of stress field, deformation field and seepage field after the pressure-relief mining, and analyze the changing law of gas parameters and seepage coefficient of the protected coal seam.(4)It is brought forward that the goaf roof of the gob-side entry retaining in the first pressure-relief seam exists three methane-rich zones with well fracture development: The ring shaped void area in goaf above the entry retaining, the vertical fracture development area in fractured zone and the fracture zones in the pressure-relief coal seams in long-distance. This result provides a theoretic reference for the drilling arrangement in the relieved drainage of coal bed methane.(5)It is the first time to brought forward the idea that the relieved methane in protected coal seam and the goaf of the near coal seam is exploited according to drilling assurgent hole from the roof of the entry retaining. The relieved drainage method of coal bed methane is created with the drilling hole of the entry retaining instead of multiple rock roadway. Moreover, the drilling arrangement scheme is designed for the relieved drainage of coal bed methane.The principle for relieved drainage of coal bed methane are successfully applied to the practice of the drilling on the ground and the underground roadway retained in Guqiao mine of Huainan coal area, and establish the relieved drainage mode which is suitable for Huainan mining area.