Numerical Simulation on Gas Drainage of Boreholes in Coal Seam Based on Gas-Solid Coupling Model
Bo Li 1,2 Jianping Wei 1 Peng Li 3
COMPUTER MODELLING & NEW TECHNOLOGIES 2014 18(12A) 418-424
1 State Key Lab Cultivation Base, Henan Province Key Lab of Gas Geology & Gas Control, Henan Polytechnic University, 2001 Shiji Road, Jiaozuo, Henan, China
2. Henan Key Laboratory of Biogenic Traces & Sedimentary Minerals, 2001 Shiji Road, Jiaozuo, Henan, China
3. Faculty of Resource and Safety Engineering, China University of Mining & Technology (Beijing), Ding 11 Xueyuan Road, Haidian District, Beijing, China
Gas pre-drainage of boreholes in coal seam is considered to be the main effective measure for preventing coal and gas outbursts. In order to research the stress changes in surrounding coal mass of drainage boreholes and the distribution of pore pressure, as well as the evolution of permeability, the methane in surrounding coal mass of boreholes was classified into two different parts, namely free gas and adsorbed gas, which were based on the law of mass conservation. Then the gas migration model of coal mass around boreholes was proposed considering the Klinkenberg effect. The deformation field equation and gas seepage equation of coal seam were deduced, and the evolution models of permeability and porosity were derived under the combined contribution of the adsorption swelling and pore-fracture compression. Afterwards, the fluid-solid coupling model was imported on the basis of the basic theory of porous media fluid-solid coupling, and the two-dimensional geometric model was implemented into the multi-physical coupling simulation software. The conclusions were obtained as follows: (1) The initial stress state was disturbed due to the presence of drainage boreholes, and the concentrated stress in the coal mass around boreholes was gradually transferred into the deep zone, which was consistent with the evolution of permeability; (2) As time goes by, the gas drainage radius gradually increased, however the growth rate reduced by degrees.