| The coal seam of Xuehu Coal Mine has the characteristics of high adsorption and low permeability.For the problem of large gas drainage engineering,poor effect,and serious impact on mining continuation,directional drilling is used to extract gas from comb holes.Reducing the amount of engineering,while also improving the efficiency of gas extraction.Through numerical simulation analysis,the paper studies the correlation law of various parameters of directional drilling comb-shaped borehole gas in Xuehu Coal Mine No.2 coal seam site,researches and determines the effective technical parameters of comb-shaped borehole effective influence radius and field test,And investigate the gas extraction effect of comb-shaped borehole.The main research results obtained by the thesis are as follows:(1)Based on the coal seam of No.2 and No.2 coal seams in Xuehu Coal Mine and on-site geological conditions,a three-dimensional numerical calculation and analysis model was created in COMSOL to reveal the correlation between factors such as extraction time and borehole diameter.It was found that there is a negative correlation between the extraction time and coal bed gas pressure,but there is a positive correlation between the effective extraction radius and the former;as time goes by,the extraction rate continues to decrease;the borehole diameter also affects the gas one of the main factors of the drainage effect.The larger the value,the better the drainage effect and the larger the effective drainage radius.The effective drainage radius of the borehole is little affected by the drainage negative pressure and can be almost ignored,but gas drainage there is a positive correlation between the volume and the extraction negative pressure.(2)According to the specific influence of different conditions of COMSOL software simulation analysis on the gas extraction effect of comb-shaped boreholes,the relevant parameters of the field test of Xuehu Coal Mine directional drilling comb-shaped borehole gas extraction were determined.The analysis shows that:(1)the longer the extraction time,the better the gas extraction effect,but the gas pressure and the effective extraction radius of the comb-shaped borehole change very slowly after 200 days;(2)when the borehole diameter increases,with the extraction carry out,the effective influence radius increases more;(3)The negative pressure increases from 15 kPa to 30 kPa,and the effective influence radius difference is less than 0.2% at 200 days of extraction.Combined with directional drilling equipment and technical requirements,as well as coal mine gas and geological conditions,it was determined that the relevant parameters of the gas extraction field test of the directional drilling comb hole in Xuehu Coal Mine are 120 mm in diameter and continuous extraction for 200 days under a negative pressure of 30 kPa at this time,the effective radius of the simulation is 3.5 m,and the hole spacing is determined to be 6 m.(3)A field test of directional drilling comb hole gas drainage was carried out in Xuehu Coal Mine 29020 wind tunnel to test and analyze the gas drainage effect.Continuously monitor the daily gas extraction volume of 7 comb-shaped boreholes.Xuehu Coal Mine directionally drilled gas reserves in the area affected by comb-shaped borehole groups.It can be calculated that the gas extraction rate is 60.6%;after 200 days of extraction,5 drilling sites are set up at the bottom of the 29020 air lane,a total of 13 sampling points,and the samples are sent to the laboratory for analysis.The results show that the maximum gas pressure is 0.57 MPa,the minimum value is 0.2MPa,the average is 0.449 MPa,and the average gas content is 4.92 m3 / t,both of which are below the critical value,which is lower than the gas control standard of Henan Province. |
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