急倾斜煤层瓦斯钻孔有效抽采范围的精准确定

Accurate determination of effective gas extraction range of gas drilling holes in steeply inclined coal seams

为了明确急倾斜煤层瓦斯抽采钻孔的有效抽采范围,合理布置抽采钻孔位置,以乌东煤矿43号煤层为例,利用数值模拟得到急倾斜煤层瓦斯钻孔有效抽采范围随时间变化规律,建立急倾斜煤层钻孔周围气体渗流单元模型,推导了急倾斜煤层有效抽采范围的数学模型并结合现场实测结果对数值模拟和数学模型进行验证,且平均相对误差率较小(均小于5%)。数值模拟结果显示:与常规煤层瓦斯钻孔有效抽采范围相比,急倾斜煤层有效抽采距离与抽采时间呈非线性关系;在抽采过程中,有效抽采范围随时间的增加,在钻孔平面不同方向上扩展速度不同,最终趋于稳定后有效抽采范围呈椭圆形区域。通过对急倾斜煤层钻孔周围煤壁上受力状态分析,认为有效抽采范围出现差异的原因主要是钻孔的出现改变了原有的地应力的分布状态,钻孔周围煤壁的稳定性遭到破坏,其附近一定范围内的煤体物理力学性质发生改变,此外,地应力的重新分布对钻孔周围煤层渗透率也产生一定影响。为定量研究垂直于钻孔二维截面上有效抽采范围随时间变化的发展趋势,通过急倾斜煤层有效抽采范围的数学模型得到急倾斜煤层有效抽采范围表达式,分析不同方向上抽采距离扩展速度造成的差异程度,对急倾斜煤层瓦斯抽采钻孔的现场应用具有一定指导作用。

In order to clarify the effective extraction range of gas drainage boreholes in steeply inclined coal seams and reasonably arrange the locations of drainage boreholes,taking Wudong Coal Mine No.43 coal seam as an example,and numerical simulations were used to ob⁃tain the effective drainage range of gas drainage holes in steeply inclined coal seams.According to the law of time change,the gas percola⁃tion unit model around the steeply inclined coal seam was established,the mathematical model of the effective drainage range of the steeply inclined coal seam was deduced,and the numerical simulation and mathematical model were verified by the field measurement results,and the average relative error rate was small(both are less than 5%).Numerical simulation results show that:compared with the effective gas drainage range of conventional coal seam boreholes,the effective drainage distance and drainage time of steep coal seams have a nonlinear relationship;during the drainage process,the effective drainage range increases with time.The expansion speed is different in dif⁃ferent directions of the borehole plane,and the effective drainage area becomes an elliptical area after finally stabilizing.Through the anal⁃ysis of the force state on the coal wall around the boreholes in steeply inclined coal seams,it is believed that the main reason for the difference in the effective extraction range is that the emergence of the boreholes has changed the original distribution of ground stress,and the stability of the coal wall around the drilling was impaired,the physical and mechanical properties of the coal in a certain range nearby change.In addition,the redistribution of ground stress also has a certain impact on the permeability of the coal seam around the borehole.In order to quantitatively study the development trend of the effective drainage range on the two-dimensional section perpendicular to the borehole with time,the mathematical model of the effective extraction range of the steep coal seam was used to obtain the expression of the effective extraction range of the steep coal seam,and the extraction in different directions was analyzed.The degree of difference caused by the ex⁃pansion speed has a certain guiding effect on the field application of gas drainage boreholes in steeply inclined coal seams.