No abstract

No abstract

To ensure the sealing effect of gas extraction borehole in underground coal mine and improve the concentration of gas extraction, a kind of high-flow sealing material which can be injected into the microcracks around borehole was developed. The ultrafine cement as the base material, with water-reducing agent, expansion agent, retarder, the material, and water combined stir, will form a kind of colloid with high fluidity and slightly expansibility. This paper analyzes the differences between the new high-fluidity sealing material and ordinary cement materials in expansion performance, compressive strength, and sealing performance. Scanning electron microscope and mercury intrusion method were used to analyze the differences in microscopic morphology and pore structure of these two materials. The experimental results show that the new high-fluidity sealing material has an excellent fluidity of 295.5 mm with an expansion rate of 60 d being 1.562%. The new high-fluidity sealing material is convenient for grouting with strong material permeability and superior sealing performance. Field test results show that the effect of the new high-fluidity sealing material is better than the ordinary cement materials. The average drainage concentration and flux during the drainage period were 59.07% and 0.243 m3/min, respectively, which showed that the drainage efficiency was significantly improved. This novel sealing material is of great significance for improving the efficiency of drilling and drainage.

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.

Gas extraction is an important way to control gas disasters. The effect of traditional gas extraction drilling on ultrathick coal seam is not well. In order to improve the rate of gas extraction, directional long drilling is used to replace conventional drilling for coal seam gas extraction. Through the combination of numerical simulation and field experimentation, the stress distribution around borehole is analyzed, and the influence of different time, different gas pressure, different negative pressure of extraction, and different permeability of coal body on directional borehole is simulated. According to the experimentation of Baode Mine, the data of gas drainage volume of conventional directional drilling are recorded and analyzed. The results indicate that the directional drilling is more suitable for Baode Mine 81306 working face of coal seam 8 gas extraction operation. Directional drilling is better than conventional drilling in work, with good drainage stability and large gas drainage volume, which can greatly reduce the outburst time and improve the gas drainage rate.