Numerical Simulation Of Gas Migration Law Of Bedding Gas Extraction In4Coal Seam Of Shaqu Mine

In recent years, with the increasing of mining depth and strength, the coal seam gas emission intensity is also growing, which seriously restrict the mine production, especially in the high gas mines. Gas extraction has become an important means of prevention and treatment of the gas disaster, gas as a clean and efficient energy resources, if taking and using the coal seam gas as far as possible, which can be transform danger into assets. According to the coal mine safe rules, the high gas coal and having gas outburst dangerous’coal seam must be pre-drainage before mining, but how to ensure the effection of gas drainage and arrange the drilling rationally has been a great challenge. Now to estimate the drainage spacing usually through field measurement. This method needs to arrange some experimental drilling and a longer observation time of the extraction.The thesis based on the selection of gas drainage methods and the layout problem of drainage drilling, viewing the coal as a dual porosity fractured media structure. The pore structure deformation may be caused by the decline of gas pressure, which affects the permeability of coal seam. The article researched the storage and percolation characteristics of coal seam from the micro to the macro level. Established coupling seepage field equation, on the basis of Darcy’s law, Fick’s first law, the continuity equation and auxiliary equations. The coupling medium was coal-rock volume strain. By means of numerical analysis software to solve the numerical model, established plane strain model and three-dimensional geometric model according4coal seam of Shaqu mine. Analyze the variation of gas pressure, Darcy velocity and permeability with time passing, and drainage effect at different borehole gas extraction method as dip direction gas extraction, dip direction inclined drilling and strike gas extraction. Study the drilling layout parameters such as spacing or angle in the impact drainage effect.The results show that closer to the location of borehole the gas pressure drop was "L" shaped, more distant position was inverted "S" type, farther away from the extraction position, the drop curve gradually becomes "L" shaped to inverted "S" type. Seepage velocity with drainage showed three stages, in a week or so comes to peak and rapid decline in subsequent, and slow decline when drainage to stable. Compare to dip direction inclined drilling and strike gas extraction, the gas pressure drop fastest in dip direction extraction in the same drainage time. There are two slower pressure reducing area in dip direction inclined drilling drainage. The affected drainage area expanded by way of fan-shaped radial type around applied drilling location in strike gas extraction, and drilling layout density greatly effect drainage.