井下顺层多分支定向长钻孔瓦斯抽采特性研究
Study on gas extraction characteristics of multi-branch directional long drillings along underground coal seam
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摘要: 煤矿井下顺层定向钻孔“大孔深、带分支”的特点使其瓦斯抽采特性与普通钻孔存在差异。通过数值模拟分析了试验矿井预抽钻孔有效影响范围随时间的变化特征,并结合矿井实际确定试验定向钻孔布置间距为5 m;设置了1个分支和2个分支2组扇形布置的试验定向钻孔组并实测抽采瓦斯纯流量,实测结果表明,试验定向钻孔抽采瓦斯纯流量随时间呈现“快速降低—较快升高—缓慢衰减”的变化趋势,抽采阶段可划分为“U”形波动期和稳定衰减期,在2个阶段抽采瓦斯纯流量与时间之间的关系分别符合三次多项式和负指数函数关系。通过实测抽采效果对比发现,“U”形波动—稳定衰减模型在预测定向钻孔抽采瓦斯总量和残余瓦斯含量时的误差均比负指数衰减模型小,更适用于定向钻孔瓦斯抽采效果预测与工程设计。Abstract: The characteristics of " ultra-deep hole,incidental branch" of directional drilling along underground coal seam make the gas drainage characteristics different from those of ordinary drilling. Firstly,the variation characteristics of the effective influence range of the pre-drainage borehole in the test mine with time were analyzed by numerical simulation. Then combined with the actual mine to determine the test directional drilling arrangement spacing of 5 m. Two groups of experimental directional drilling groups with fan-shaped arrangement of 1 branch and 2 branches were set up and the pure quantity of drainage was measured. The measured results show that the pure quantity of drainage by directional drilling shows a trend of rapid decreasefast increase- slow attenuation with time. The extraction stage can be divided into " U" type fluctuation period and stable attenuation period. In the two stages,the pure quantity and time of gas drainage respectively conform to the cubic polynomial relationship and the negative exponential function relationship. By comparing the predicted results with the measured results,it is found that the total amount of directional drilling extraction and residual gas content predicted by the "U" type model are more accurate than the negative exponential decay model. It is more suitable for the prediction of the gas drainage effect of directional drilling and engineering design.