Optimization of multi-hole hydraulic cutting combined extraction parameters under superposition effect
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摘要: 针对低透高瓦斯煤层在水力割缝过程中存在割缝扰动范围不清、割缝钻孔最佳布孔间距不明确的问题，以贵州豫能高山煤矿1908工作面为研究背景，在建立水力割缝煤体瓦斯抽采流固耦合模型的基础上，借助COMSOL数值模拟软件对高山煤矿1908工作面水力割缝钻孔有效抽采半径、孔周瓦斯压力变化情况进行了研究，并依据模拟结果深入分析了水力割缝钻孔在多孔布置时，受孔间抽采叠加效应影响下有效抽采范围及孔间瓦斯压力变化情况，最终得出其最佳布孔间距及抽采时间。结果表明：① 水力割缝钻孔单孔抽采效果随割缝深度显著提升，但钻孔有效抽采半径增速变缓，为得到最佳割缝深度，对各钻孔有效抽采半径进行三项式拟合，随着水力割缝深度的增加，有效抽采半径范围在快速增加后放缓且最终趋于平稳，并得出了高山煤矿最佳割缝深度为1.5 m，有效抽采半径达为3.1 m。② 在相同抽采时间下，煤体内瓦斯压力随两孔距的缩短而降低，说明孔间距越小，孔间受水力割缝所造成的扰动越剧烈，抽采叠加效应影响越显著。③ 在保证消突达标的前提下，选择孔距为7 m进行水力割缝钻孔布置效果最佳。④ 原本在“正方形”布孔方式中，孔心位置可能出现抽采盲区的点最大瓦斯压力仅为0.67 MPa，小于临界值，“正方形”布孔较“正三角”布孔的有效覆盖面积更大且减少了抽采重复区域，从而减少了钻孔施工量，提高了瓦斯治理效率。⑤ 通过现场试验得出在60 d抽采周期内，水力割缝钻孔布置采用孔距为7 m的“正方形”布孔可有效提高瓦斯抽采浓度及抽采纯量，并达到了延长高效抽采周期的效果，且可消除孔间煤体瓦斯抽采空白带，实现孔间区域煤体消突达标。Abstract: In the process of hydraulic cutting in low permeability and high gas coal seams, there are problems such as unclear cutting disturbance range and unclear optimal hole spacing for cutting drilling. In order to solve the above problems, the 1908 working face of Gaoshan Coal Mine in Yuneng, Guizhou Province is taken as the research background. On the basis of establishing the fluid-solid coupling model of gas extraction in coal body with hydraulic cutting, with the help of COMSOL numerical simulation software, the effective extraction radius of hydraulic cutting borehole and the change of gas pressure around the borehole in the 1908 working face of Gaoshan Coal Mine are studied. Based on the simulation results, the effective extraction range and gas pressure change between holes are analyzed under the influence of the extraction superposition effect between holes when the hydraulic cutting drilling holes are arranged in multiple holes. Finally, the optimal hole spacing and extraction time are obtained. The results show the following points. ① The single hole extraction effect of hydraulic cutting drilling is significantly improved with the cutting depth. However, the effective extraction radius of the borehole increases slowly. In order to obtain the best cutting depth, the effective extraction radius of each borehole is fitted in a trinomial way. With the increase of hydraulic cutting depth, the range of effective extraction radius slows down after rapid increase and finally tends to be stable. The optimal cutting depth of Gaoshan Coal Mine is 1.5 m, and the effective extraction radius is 3.1 m. ② Under the same extraction time, the gas pressure in the coal body decreases with the shortening of the distance between two holes. It shows that the smaller the hole spacing is, the more serious the disturbance caused by hydraulic cutting between holes is, and the more significant the influence of the extraction superposition effect is. ③ On the premise of ensuring that the outburst elimination meets the standard, it is best to choose a hole spacing of 7 m for arranging hydraulic cutting drilling. ④ Originally, in the "square" hole arrangement, the maximum gas pressure at the point where the blind area may occur at the hole center is only 0.67 MPa, which is less than the critical value. The effective coverage area of the "square" hole arrangement is larger than that of the "triangle" hole arrangement, and the repeated area of drainage is reduced. This reduces the amount of drilling and improves the efficiency of gas control. ⑤ Through field test, it is concluded that in the 60 d extraction period, the hydraulic cutting drilling arrangement with a hole spacing of 7 m and a "square" hole arrangement can effectively improve the concentration and purity of gas extraction. It can also extend the period of high efficiency extraction. It can eliminate the blank zone of gas extraction in the coal body between boreholes to eliminate the outburst of the coal body in the area between boreholes.
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图 2 抽采60 d后各钻孔四周煤体瓦斯压力分布
Figure 2. The gas pressure distribution around each borehole after 60 days of extraction
图 4 有效抽采半径随割缝深度变化趋势
Figure 4. The variation trend of the effective extraction radius varies with the cutting depth
图 6 不同孔距钻孔瓦斯压力随抽采时间变化云图
Figure 6. Cloud chart of gas pressure variation with extraction time in boreholes with different borehole spacing
图 7 不同孔距及抽采时间下孔周瓦斯压力分布曲线
Figure 7. Distribution curves of borehole gas pressure under different borehole distance and extraction time
图 9 不同布孔方式的瓦斯抽采空白区域对消突的效果
Figure 9. Outburst elimination effect of gas extraction blank zone with different borehole layout methods
图 10 不同布孔方式抽采60 d孔周瓦斯压力分布曲线
Figure 10. Gas pressure distribution curve around boreholes for 60 days with different borehole layout methods
图 12 未使用水力割缝的抽采钻孔瓦斯参数
Figure 12. Gas parameters of extraction boreholes without hydraulic cutting
图 13 水力割缝抽采钻孔瓦斯参数
Figure 13. Gas parameters of extraction borehole with hydraulic cutting
表 1 数值模拟基础参数
Table 1. Numerical simulation of the basic parameters
参数 参数值 煤层初始瓦斯压力/MPa 1.04 孔隙率 0.048 煤体初始渗透率/m2 5.7×10−15 割裂煤体渗透率/m2 3.4×10−11 煤密度/(kg·m−3) 1 492 瓦斯密度/(kg·m−3) 0.719 泊松比 0.29 黏聚力/MPa 0.92 瓦斯动力黏度/(Pa·s) 1.71×10−5 空气动力黏度/(Pa·s) 1.07×10−5 
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表 2 试验测点残余瓦斯压力、瓦斯含量
Table 2. Residual gas pressure and gas content of test measuring points
孔号 残余瓦斯压力/MPa 残余瓦斯含量/(m3·t−1) 抽采率/% 1 0.61 2.7 62.50 2 0.57 3.3 54.17 3 0.59 3.1 57.04 4 0.62 2.9 59.72
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