Study on gas extraction from parabolic high level drilling during the initial mining period of fully mechanized caving face
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摘要: 针对采用常规高位定向长钻孔在工作面初次来压期间瓦斯抽采效果不佳的问题,以中煤华晋集团有限公司王家岭矿12309综放工作面为工程背景,通过物理相似模拟和数值计算分析了初采期综放工作面煤层顶板覆岩结构和裂隙发育规律:初采期的煤层顶板裂隙发育高度低、数量少,随着工作面的推进,顶板裂隙逐步发育,裂隙发育的高度和范围随着推进距离的增加而增大,裂隙最大发育高度约为28 m,工作面来压步距约为50 m;初采期工作面瓦斯浓度和涌出量较大,沿工作面倾向,瓦斯浓度从20~150架支架逐渐增大,沿工作面走向,由煤壁300 mm至后刮板输送机瓦斯浓度逐渐增大,采空区瓦斯涌出量占工作面瓦斯涌出量的50%以上,瓦斯涌出量整体上呈上升趋势,且有明显的阶段性特征。根据现场实际情况和初采期综放工作面瓦斯涌出特征、覆岩结构及裂隙演化规律,对初采期的常规高位定向钻孔的轨迹进行了优化设计,提出了初采期抛物线型高位定向钻孔瓦斯抽采方法。将钻孔的终孔位置设计在煤层里,与采空区直接导通,用于工作面初采期采空区低位瓦斯抽采,解决了初采期常规高位水平长钻孔层位较高的问题。现场应用结果表明:相比于常规高位定向钻孔,采用抛物线型高位定向钻孔可在工作面采空区基本顶初次来压前有效抽采采空区低位瓦斯,瓦斯抽采纯量平均提高了约37%,上隅角和回风流最大瓦斯体积分数均小于0.80%,达到了瓦斯抽采的预期效果。Abstract: The gas extraction effect during the initial pressure on the working face by using conventional high-level directional long drilling is poor. In order to solve the above problem, taking the project background of 12309 fully mechanized caving face of Wangjialing Mine of China Coal Huajin Group Co., Ltd. as an example, the paper analyzes the overburden rock structure and fracture development law of the coal seam roof in the fully mechanized caving face during the initial mining period by physical similar simulation and numerical calculation. During the initial mining period, the height of fractures is low and the number of fractures is small in the coal seam roof. With the advancement of working face, the roof fractures gradually develop, the height and range of fractures increase with the increase of advancement distance. The maximum height of the fractures is about 28 m, and the pressure step distance of the working face is about 50 m. During the initial mining period, the gas concentration and emission volume of the working face are relatively large. Along the working face tendency, the gas concentration gradually increases from 20 to 150 supports. Along the working face direction, the gas concentration gradually increases from 300 mm of the coal wall to the rear scraper conveyor. The gas emission volume of the goaf mining area accounts for more than 50% of the gas emission volume of the working face, and the gas emission volume as a whole is on an upward trend with obvious phase characteristics. According to the actual situation of the site and the gas emission characteristics, overburden rock structure and fracture evolution law of the fully mechanized caving face during the initial mining period, the trajectory of the conventional high-level directional drilling during the initial mining period is optimized, and the parabolic high-level directional drilling gas extraction method during the initial mining period is proposed. The final hole of the borehole is designed in the coal seam, which is directly connected with the goaf mining area and used for low level gas extraction in the mining area during the initial mining period of the working face. It solves the problem of high level of conventional high-level long borehole during the initial mining period. The field application results show that compared with the conventional high-level directional drilling, the use of parabolic high-level directional drilling can extract the low level gas in the goaf mining area effectively before the initial pressure of the basic roof of the working face. The average pure volume of gas extraction increases by about 37%, and the maximum gas volume fraction in the upper corner and return air flow is less than 0.80%. The result has achieved the expected effect of gas extraction.
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