Study On The Pressure Relief Mechanism Of Upper Protective Seam Mining And Gas Extraction Technology In Close Coal Seams

Many coalfields in China are faced with close distance coal seams in present days, featured by high-gas, low permeability and potential risk of coal and gas outburst which increase the difficult of mining safety and decrease the profit of the mine. Demonstrated by practices, the combination of mining protective layer and the antireflection effect through pressure relief of the protected layer and rational gas extraction activities is the most effective regional control technology.In allusion to the upper protective layer mining problem under the complex conditions of low permeability, high-gas and potential risk of coal and gas outburst of close coal seams in Shaqu coalmine, by using the method of theoretical analysis, numerical simulation and field test, we studied the mechanism of roof and floor strata movement and deformation, the distribution of stress, the fracture development, the permeability development of the protected layer, pressure relief gas migration and storage, gas emission in working face, the interaction between mining-induced fractures field and stress-relieved gas migration. The destroyed floor depth of upper protective layer mining and stress-relief protective range is determined by the method of theoretical analysis and numerical simulation. Numerical simulation on the dynamically process of overlying rock collapse lead to the mechanism of roof and floor strata movement and the stress and displacement distribution of protected layers during upper protective layer mining, and the impacts of different factors on pressure relief effect. We built up the technical system of simultaneous extraction of coal and gas as upper protective layer mining, analyzed the influence of distribution of gas drainage on the gas drainage effect and assessed the field application effect of upper protective layer mining. The result of field test shows that the average output of upper layer mining is 1077t/d, the average gas extraction rate is 55.77%, which is 78.3% in protected layers.The result of research indicates that No.2 coal layer of Shaqu coalmine being mined as protective layer has an enormous effect on the pressure relief of downward layer, which achieved the goal of prevention of coal and gas outburst and safe and efficient coal and gas simultaneous extraction.