Abstract
Gas drainage is an important means of gas control. The influence of the key position of the sealing hole on gas drainage was studied by theoretical and numerical simulation combined with field measurement to solve low gas concentration in gas predrainage boreholes in coal mines of China. By analyzing the distribution of cracks around the boreholes and the law of air leakage and simulating the drainage effect of different sealing areas (8 m, 12 m, and 16 m), it was proposed that the key position of the sealing hole should be in the prepeak stress concentration area. According to the actual situation of Baode Mine, the sealing test scheme of different sealing areas was put forward, and the field test was carried out to obtain the key sealing area of gas predrainage boreholes in Baode Mine. Research shows that when the sealing area is 8–16 m, the average gas concentration is 63.57%, and the average pure gas flux is 0.408 m3/min. The sealing effect of this area is better, with fewer cracks, than that of the existing sealing area, effectively preventing gas leakage and increasing the gas concentration and gas scalar.
Highlights
Coal, as China’s main energy, is vital for China’s economy
As the borehole of coal seam is constructed on the side of the roadway, the gas leakage and seepage characteristics of the borehole are inevitably affected by the stress changes around the roadway [36]
As free air leakage area (FAA) and semifree air leakage region (SAA) have higher permeability than the other two areas and are adjacent to the roadway, gas leakage is more likely to occur there. e sealing section should exceed FAA and SAA to form a leak-proof area composed of hard-toair leakage area (HAA) sections to effectively prevent air leakage
Summary
As China’s main energy, is vital for China’s economy. the mining process is faced with production unsafety, especially coal mine gas disasters [1, 2]. Most gas drainage boreholes in coal seam can drill more than 200 meters, and the sealing length is generally 10–15 meters, and the length of the extraction gas chamber is more than 185 meters. To give full play to the drainage effect of the gas drainage system, this study, based on the coal deposit conditions and mining conditions of Baode Coal Mine, the concept of key positions of the hole sealing was put forward, analyzed the distribution of coal wall fractures and the gas leakage and seepage law zone around the borehole, and proposed sealing test plan for different sealing areas. Field tests were carried out in the 81310 return airway of Baode Coal Mine, and the variation laws of the extraction concentration and gas purity of the extraction borehole in different sealing areas were analyzed. No large-scale faults, folds, and collapse columns have been found. e 8# coal seam is located above the S3 sandstone at the bottom of the Shanxi Formation (P1S), and the coal thickness varies from 2.15 to 10.50 m, with an average of 7.36 m. e thickness of pure coal is 1.85–9.20 m, with an average of 6.02 m; they are thick-to-extrathick coal seams, mainly thick coal seams. e structure of the coal seam is complex, containing 0∼8 layers of gangue, and the total thickness of the gangue is 0∼3.84 m, with an average of 1.38 m. e direct roof of the coal seam is mostly sandy mudstone and mudstone, and the part is coarse sandstone. e floor is mainly mudstone, followed by siltstone. e thickness variation coefficient of 8# coal seam is 27.5%. e main coal seam includes a thick coal seam and an extrathick coal seam and gradually becomes thicker from east to west. e extrathick coal seam is distributed in the northwest and southeast of the mining area, and the medium-thick coal seam is in the northern boundary of the mining area
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