Abstract
In order to analyze the influence degree of different factors on gas extraction radius, on the basis of coal seam gas flow theory and elastic mechanics, considering the influence of coal seepage rate change on gas flow, the COMSOL Multiphysics numerical simulation software is secondarily developed by using the stress-seepage coupling mathematical model of coal and rock containing gas. Taking coal seam No.2 of Juji Coal Mine as an example, the effective extraction radius under different extraction negative pressure, extraction borehole diameter, extraction time, and initial permeability of coal seam are simulated, respectively. Then, the orthogonal test method is used to design different calculation schemes, and the effective extraction radius is used as the judgment index. The simulation software is used to calculate the effective extraction radius corresponding to different influencing factors. SPSS statistical software is used to analyze the parameters. The multivariate linear regression equation of the influencing factors of the effective extraction radius is obtained, and the multivariate linear regression model is established. The results show that the negative pressure of extraction has little effect on the effective extraction radius; the effective extraction radius gradually expands with the increase of extraction time and extraction aperture, but it has certain timeliness. The initial permeability of the coal seam has a great influence on the effective extraction radius. The influence degree of different influencing factors from large to small is the initial permeability of coal seam, extraction time, borehole diameter, and extraction negative pressure. Therefore, the key to improving the effectiveness of gas extraction is to increase the initial permeability of the coal seam before preextraction, ensure sufficient extraction time, appropriately increase the borehole diameter, and improve the negative pressure of extraction. Finally, the gas flow rate is used for a field test, and the measured results are basically consistent with the simulation results, which proves the correctness of the mathematical model of gas-containing coal and the feasibility of using numerical simulation methods to study the effective extraction radius of coal seams.
Highlights
For outburst mines, preextraction of coal seam gas is a very important outburst prevention measure
In the process of gas extraction, the decrease of pore pressure of coal [25, 27], the desorption effect of coal matrix, and the change of effective stress will lead to the continuous change of coal permeability. e relationship between the two is a typical grey system, which is difficult to quantitatively study. erefore, this paper studies the influence of initial permeability on effective drainage radius from the initial permeability of coal seam before pumping without drilling
Design and Results of Orthogonal Test Scheme e effective gas extraction radius of the borehole is an important basis for selecting extraction methods and determining borehole layout parameters [30]. ere are many factors affecting the effective gas extraction radius, but the size of the effective gas extraction radius is mainly related to the factors such as borehole diameter, extraction time, initial permeability, and extraction negative pressure
Summary
Preextraction of coal seam gas is a very important outburst prevention measure. In this paper, based on the comprehensive consideration of coal skeleton deformation, coal pore pressure, and adsorption expansion force during gas extraction, the stressseepage gas-solid coupling model during gas extraction is used, and the drilling model is established in the numerical software COMSOL Multiphysics to simulate the gas extraction of coal seam No. in Juji Coal Mine. E effective gas extraction radius of the borehole was measured by using the gas flow method in the mining area of the lower drainage roadway of Juji Coal Mine 2616 so as to verify the correctness of the coupling model of coal rock containing gas and the feasibility of using COMSOL software to simulate the effective gas extraction radius of coal seam drilling The multivariate linear regression analysis of each factor was carried out by using the statistical analysis software SPSS, and the regression equation of each factor was obtained. e multivariate linear regression equation of the effective gas extraction radius was established. e effective gas extraction radius of the borehole was measured by using the gas flow method in the mining area of the lower drainage roadway of Juji Coal Mine 2616 so as to verify the correctness of the coupling model of coal rock containing gas and the feasibility of using COMSOL software to simulate the effective gas extraction radius of coal seam drilling
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