低透气突出煤层水力割缝协同卸压增透技术

Hydraulic cutting cooperative pressure relief and permeability enhancement technology in low permeability outburst coal seam

  • 摘要: 针对单一水力割缝对于低透气性厚煤层或存在夹矸煤层的增透卸压效果不理想的问题,以冀中能源有限公司东庞煤矿21212工作面为研究背景,提出了上下煤层水力割缝协同卸压增透技术:根据煤层具体构造,在上下煤层各自进行一次水力割缝施工,上下煤层的2个槽缝产生的裂缝继续起裂、扩展与延伸,致使水力割缝孔之间的煤体裂隙充分发育,形成互相贯通的立体裂隙网络,产生协同卸压增透作用,扩大有效抽采半径。为更加合理布置水力割缝试验孔间距,采用FLAC 3D软件建立了水力割缝协同卸压物理模型,确定了水力割缝水压为30 MPa、出煤量为4.5 m3(缝宽为0.3 m,缝深为1.57 m,上下煤层双割缝)和出煤量为6 m3(缝宽为0.3 m,缝深为1.78 m,上下煤层双割缝)的煤岩的理论有效抽采半径分别为4.5 m和4.8 m。为确定水力割缝的增透效果,对比了出煤量为4.5 m3的试验孔S1和出煤量为6 m3的试验孔S2与不割缝钻孔的抽采效果,结果表明:不割缝钻孔的平均瓦斯抽采体积分数为22.38%,平均瓦斯抽采纯量为0.206 m3/min;割缝钻孔S1的平均瓦斯抽采体积分数为75.73%,平均瓦斯抽采纯量为0.382 m3/min;割缝钻孔S2的平均瓦斯抽采体积分数为86.91%,平均瓦斯抽采纯量为0.454 9 m3/min。与不割缝钻孔相比,采用水力割缝增透措施后,煤层透气性得到很大提高,瓦斯抽采体积分数提高了约4倍,瓦斯抽采纯量提高了2倍左右,瓦斯抽采效果好。根据瓦斯压力降低法实测有效抽采半径,可得出煤量为4.5,6 m3的水力割缝的有效抽采半径与抽采时间的关系,抽采时间为30,60,120,180 d时,出煤量为4.5 m3的水力割缝的有效抽采半径为4.9,5.5,6.1,6.5 m,出煤量为6 m3的水力割缝的有效抽采半径为5.1,5.6,6.3,6.7 m。综合考虑,最后得到了适合东庞煤矿的水力割缝技术施工参数:出煤量为4.5 m3,抽采时间为60 d,有效抽采半径为5.5 m,钻孔间距为7.7 m。

     

    Abstract: The effect of a single hydraulic cutting is not very ideal for thick coal seam with low permeability or coal seam with gangue to increase the permeability and release the pressure. In order to solve the above problem, taking the 21212 working face of Dongpang Coal Mine of Jizhong Energy Co. as an example, this paper proposes hydraulic cutting cooperative pressure relief and penetration enhancement technology in the upper and lower coal seam. According to the specific structure of coal seam, the hydraulic cutting construction is carried out once in the upper and once in the lower coal seam. The fractures generated by the 2 slots in the upper and lower coal seam continue to crack, expand and extend, resulting in the full development of coal fissures between the hydraulic cutting holes, forming a three-dimensional fissure network connected with each other. The network generates cooperative pressure relief and penetration enhancement effects, and expands the effective extraction radius. In order to arrange the test hole spacing of hydraulic cutting more reasonably, FLAC 3D software is used to establish a physical model of hydraulic cutting cooperative pressure relief. The hydraulic cutting water pressure is 30 MPa. One coal output is 4.5 m3 (cutting width is 0.3 m, seam depth is 1.57 m, double cutting in the upper and lower coal seams). Another coal output is 6 m3 (cutting width is 0.3 m, seam depth is 1.78 m, double cutting in the upper and lower coal seams). The theoretical effective extraction radii of these two types of coal rock are 4.5 m and 4.8 m respectively. In order to determine the effect of hydraulic cutting, the extraction effect of test hole S1 with coal output of 4.5 m3 and test hole S2 with coal output of 6 m3 and non-cutting extraction hole. The results show that the average volume fraction of gas extraction in the non-cutting extraction hole is 22.38% and the average pure volume of gas extraction is 0.206 m3/min. The average volume fraction of gas extraction in the cutting extraction test hole S1 is 75.73% and the average pure volume of gas extraction is 0.382 m3/min. The average volume fraction of gas extraction in the cutting extraction test hole S2 is 86.91%, and the average pure volume of gas extraction is 0.454 9 m3/min. Compared with the hole without cutting, after adopting hydraulic cutting to increase permeability, the permeability of coal seam is greatly improved. The gas extraction volume fraction is increased by about 4 times, the gas extraction volume is increased by about 2 times, and the gas extraction effect is good. According to the actual measured effective extraction radius of gas pressure drop method, the relationship between the effective extraction radius and extraction time of the coal output of 4.5 m3 and 6 m3 hydraulic cutting can be obtained. When the extraction time is 30 d, 60 d, 120 d and 180 d, the effective extraction radii of the 4.5 m3 hydraulic cutting process are 4.9 m, 5.5 m, 6.1 m and 6.5 m. And the effective extraction radii of the 6 m3 hydraulic cutting are 5.1 m, 5.6 m, 6.3 m and 6.7 m. After comprehensive consideration, the construction parameters of hydraulic cutting technology suitable for Dongpang Coal Mine are finally obtained. The coal output is 4.5 m3, the extraction time is 60 days, the effective extraction radius is 5.5 m, and the hole spacing is 7.7 m.

     

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