Abstract
Owing to the exhaustion of shallow coal resources, deep mining has been occupied in coal mines. Deep buried coal seams are featured by the great ground stress, high gas pressure, and low permeability, which boost the risk of gas disasters and thus dramatically threaten the security about coal mines. Coal seam gas pressure and gas content can be decreased by gas extraction, which is the primary measure to prevent and control mine gas disasters. The coal mass is simplified into a continuous medium with dual structure of pores and fractures and single permeability. In consideration of the combined effects of gas slippage and two-phase flow, a hydraulic-mechanical coupling model for gas migration in coals is proposed. This model involves the equations of gas sorption and diffusion, gas and water seepage, coal deformation, and evolution of porosity and permeability. Based on these, the procedure of gas extraction through the floor roadway combined with hydraulic punching and ordinary drainage holes was simulated, and the gas extraction results were used to evaluate the outburst danger of roadway excavation and to verify the engineering practice. Results show that gas extraction can reduce coal seam gas pressure and slow down the rate of gas release, and the established hydraulic-mechanical coupling model can accurately reveal the law of gas extraction by drilling and punching boreholes. After adopting the gas extraction technology of drilling and hydraulic punching from the floor roadway, the remaining gas pressure and gas content are reduced to lower than 0.5 MPa and 5.68 m3/t, respectively. The achievements set a theoretical foundation to the application of drilling and punching integrated technology to enhance gas extraction.
Highlights
As the depth of coal mining increases, the gas pressure and content in coals have increased
This paper considers the combined effect of gas slippage effect and two-phase seepage, and a hydraulic-mechanical coupling model is established for gas extraction from coal seams involving equations of the gas seepage field, water seepage field, and stress field and embeds the mathematical equations into a finite set of equations
The gas pressure decreases in coal seam, and the reduction range gradually expands until it extends to the entire coal seam
Summary
As the depth of coal mining increases, the gas pressure and content in coals have increased. With regard to the gas migration in coals, the interaction between coal and gas has been explored by numerous scholars They believe that changes in coal seam forces and changes in gas pressure will deform the coal body, causing changes in porosity and permeability, and proposed many gas-solid coupling models. The gas-solid coupling model of coal and gas under different stress conditions was demonstrated by Wang et al [5], Yang et al [6], and Connell [7]. This paper considers the combined effect of gas slippage effect and two-phase seepage, and a hydraulic-mechanical coupling model is established for gas extraction from coal seams involving equations of the gas seepage field, water seepage field, and stress field and embeds the mathematical equations into a finite set of equations. The research results have guiding significance for the optimization of drainage hole layout
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