Optimization Of Gas Drainage Process And Research On CO₂ Enhanced Coal Seam Technology In Baode Coal Mine

Baode Coal Mine is the only high gas mine in the Shendong Coal Group of the National Energy Group,which is located in Shanxi Province.The enable mining coalbed contains 4 layers,and now the No.8 layer is being mined.According to the mines' gas grade appraisal report of 2018,the relative gas emission is 11.08 m3/t and the absolute gas emission is 78.48 m3/min.With the development of mine exploitation to the deep area,the amount of gas emission from coal seams has increased significantly,and the gas control has becoming more and more difficult.In addition,because of the poor permeability of coal seam,unreasonable drilling arrangement,poor sealing effect and other reasons.The effect of gas extraction in coal seam often fails to achieve the expected effect in a short time.In order to systematically analyze the gas occurrence law of No.8 coal seam,gas extraction method of working face and liquid CO₂ permeability enhancement technology of original coal seam,The 81506 standby mining face of No.8 high gas coal seam in Baode coal mine is taken as research object and the theoretical analysis,numerical simulation and field test methods are applied.The main conclusions are as follows:1)The maximum measured gas pressure in No.8 coal seam of Baode Coal Mine is 0.40 MPa,the gas content is 7.5 m3/t,the permeability coefficient of coal seam is0.4215 m2/d?MPa2.d?,and the gas attenuation coefficient is 0.0344 d-1,which belongs to the extractable coal seam.2)In order to optimize sealing technology,18 groups of comparative tests were carried out with different sealing materials,sealing length and sealing plugs under the existing conditions of the extraction system based on the parameters of coal seam gas extraction.The results indicate that the new material of AB is sealed with a sac bag,and when the sealing length is 8¹6m,the sealing performance of the hole is good.3)The extraction radius of No.8 coal seam was investigated by COMSOL simulation software.Under the condition of satisfying the minimum pre-extraction rate,the effective drainage radius of No.8 coal seam is 2 meters within 30 days,3meters within 60 days,5 meters within 90 days and 8 meters within 180 days.4)For the purpose of reducing the gas drainage time and considering the mine production and normal mining succession,a 3-factor and 3-level orthogonal experiment was carried out to study the liquid CO₂ fracturing and anti-reflection.When the length of the pre-cracking borehole is 220 m,the length of the pre-crackingis 40 m,the pre-cracking depth is 50 m,and the average gas drainage concentration of the borehole is 80.8%,it is superior to the observed boreholes of other parameters.Finally,four groups of fracturing experiments with different spacing of boreholes have been carried out to study the effect of extraction,within the same extraction range?100m?.Considering the number of boreholes,extraction time and gas drainage volume,the most reasonable distance between pre-cracked boreholes is15 m.At this time,the gas flow rate of 100-meter boreholes is increased by 3-5 times,the amount of boreholes reaching standard in working face is reduced from 34540 m to 11513 m,and the construction time of boreholes is shortened from 115 days to 39 days,which shortens the time of meeting standard in working face,ensures the normal production succession,and realizes the high-yield and high-efficiency production in mine.