The Mechanism Research Of Gas Drainage Drilling Method

Coal is the primary energy source in China. In the process of coal production, the disasters of gas have seriously affected the safety. Meanwhile, the coal gas is a kind of precious resource with very high calorific value. In our country, the reserve of coal gas is as large as natural gas reserve.How to make good use of coal mine gas is the focus of the world study. Gas drainage from boreholes is a main method of utilization and management of coal seam gas.The law of gas in the coal seam is the basic problem in the research of mine gas drainage and prevention of disaster caused by gas, and it provides important theoretical and engineering guidance for gas drainage. Based on the characteristics of the coal rock, by using the theory of Fluid-structure interaction, Finite element and Numerical simulation method, this paper conducted the research systematically into seam gas migration on the coal and gas drainage from boreholes. The main research results are followed:(1) The basic physical properties of the coal rock are described. Based on the deformation mechanism of coal mine and the definition of the porosity, the equation of porosity in coal rock containing gas is deduced. By using the effective stress in porous media theory (Terzaghi effective stress theory) and a series of assumptions, the deformation equations of coal rock is derived, and the relevant parameters of gas migration are discussed. The mathematical expression of the permeability is derived based on Carman-Kozeny equation. Based on a series of basic assumptions of gas migration and the principle of conservation of mass, the equation of gas migration is derived.(2) The analysis and research have been conducted to the law of the variation of gas migration under different conditions of single-hole drainage. Early in the gas drainage, the change of underground pressure is greater and gas pressure gradient is larger. With the advance of gas drainage, the area of gas drainage is gradually expanded; the effective stress is increasing; porosity and permeability of coal decreases, gas drainage is more difficult. The analysis and research have been conducted to the changes and distribution of gas pressure, porosity and permeability under the conditions of different burial depth and different negative pressure. The diagram of effective drainage radius and time is obtained by the analysis of gas drainage under different drainage radius conditions. The analysis has been conducted to the impact of different initial permeability on gas drainage, and the result is that the larger the initial, permeability, the more easily gas drainage is.(3) Conduct field experiments in a coal mine in Yangquan return airway, in the same coal seam drainage hole in ordinary gas drainage drilling, hydraulic punching gas drainage and high-pressure water cutting technology to gas drainage comparison of the three programs.Hydraulic cutting technology and recycling in the fissures of coal, increasing coal in air exposed area, while the formation of the gas flow channel, to speed up the gas desorption, improve gas drainage effect. Gas emissions compared to ordinary drilling, hydraulic cutting technology to make gas emissions by improving the4.11-4.34times.Hydraulic punching in this experiment did not increase substantially the actual coal seam fracture, but the process of drilling punching, drilling washed away plugging cracks in the coal particles, also play a certain degree of increase role drilling fractures, compared to ordinary drilling, gas emissions by improving the0.46-0.56times.Hydraulic punching technology compared with hydraulic cutting technology, which is more realistic value.