Abstract
In order to effectively solve the problem of gas concentration overrun in the upper corner of goaf and tailentry during the mining of panel 9303 in Anshun Coal Mine, based on the advantages of controllable trajectory and wide coverage area of directional drilling technology, high directional long boreholes are arranged in tailentry 9303 to extract pressure relief gas. Firstly, the principle of high directional long borehole drainage technology is introduced, and the fracture evolution of overlying strata is obtained through using numerical simulation, theoretical calculation, and field practice, and the fracture evolution range is determined to be 6–12.69 m, and rationality of fracture height obtained by theoretical analysis and numerical simulation is verified by the method of field borehole peep observation. Through the analysis, it is concluded that the best location of the final hole is within the range of 6–12.69 m of the roof of coal seam 9#. The field practice has proved that the final hole position of the high directional long borehole is arranged at 12 m from the roof of coal seam 9#, and the average gas extraction concentration can reach 40%–50% after the borehole enters the stable extraction stage, the purity of gas extraction is up to 8.5 m3/min, and the gas concentration in the upper corner of panel 9303 is stable below 0.5% during mining, which achieves good gas drainage and control effect and provides a new way for gas control under similar geological conditions.
Highlights
Introduction e coal resource in GuizhouProvince is very abundant, known as “Jiangnan Coal Sea.” e coal industry is one of the pillar industries in Guizhou Province, but coal seam gas content is generally high in Guizhou Province; coal and gas outburst disasters are serious
E above empirical formula calculation and numerical simulation results show that when the working face advances to 110 m, the working face reaches full mining, the height of the “three zone” of the overlying strata is basically stable, and the maximum fracture zone is 12.69 m. erefore, the high directional long borehole should be arranged in the position of about 12 m of the coal seam roof
Considering the results of empirical formula calculation and numerical simulation, and according to the field measurement verification, it can be seen that the hole arrangement layer of gas directional drilling in goaf of panel 9303 is selected at 12 m above coal seam 9#
Summary
E above empirical formula calculation and numerical simulation results show that when the working face advances to 110 m, the working face reaches full mining, the height of the “three zone” of the overlying strata is basically stable, and the maximum fracture zone is 12.69 m. In order to analyze the development of fracture at different heights, so as to determine the fracture zone of the overlying strata on the roof, the borehole images of the same borehole with the advance of the working face in different periods and depths are intercepted, as shown in Figures 9 and 10.
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