采煤工作面顶板含水层井下疏水钻孔涌水规律数值分析

Analysis of water inrush from boreholes for drainage of confined aquifer by upward boreholes in underground coal mining face

通过向采煤工作面顶板充水含水层集中施工探(疏)放水钻孔,预先疏降覆岩含水层中的地下水是顶板水害治理的主要手段,而疏水含水层水文地质参数(水压、渗透能力、含水层厚度等)与疏水钻孔空间结构(钻孔倾角、深度、孔径等)是影响井下疏水钻孔涌水规律主要因素。通过分析充水含水层与井下疏水钻孔间的流态转化特征,研究了钻孔涌水量动态衰减规律,以COMSOL软件为模拟分析平台,提出采用无限元域方法把疏水含水层概化成无限无补给含水层、有限元三角四面体结构剖分模型,钻孔单元、钻孔孔壁概化成达西渗流溢出边界,以及以孔壁为域通过实时达西流速积分计算钻孔涌水量的工作面疏水钻孔涌水数值模型构建方法。以彬长矿区某采区首采工作面井下单降深似稳定流放水试验为背景,模拟得出疏水钻孔涌水达到似稳定状态时等水头面以疏水钻孔为中心呈"反漏斗"状态,模拟计算的钻孔涌水量衰变曲线与实测结果基本一致,符合一阶单指数衰变数学模型。多场景模拟研究了不同含水层水文地质特征、疏水钻孔结构参数影响下单疏水钻孔的涌水衰变规律,结果显示:随着含水层初始水头、渗透系数增加,井下疏水钻孔峰值水量、似稳定水量呈线性增加趋势,对钻孔涌水似稳定周期影响不大;随着含水层弹性给水度的增加,钻孔峰值水量有所增加,似稳定水量基本保持不变,由于消耗静储量需要的水量增加钻孔涌水过程的似稳定周期增加明显;随着钻孔揭露含水层斜长与孔径的增加,井下疏水钻孔的峰值与似稳定涌水量亦增加。另外,以计算机工作站为硬件平台,通过构建群孔干扰疏水计算机模型,模拟得出随着疏水钻孔数目和钻孔覆盖范围的增加,含水层水头被疏降的范围增加明显,群孔疏水干扰下单孔与钻场涌水能力均减少明显,其中钻场中心钻孔疏水能力受干扰最大。

Drilling holes into the roof aquifer of coal mining face to reduce groundwater in the aquifer is one of the main measures to control the roof water hazard in coal mines.The hydrogeological parameters of aquifer(water pressure,permeability,aquifer thickness,etc.)and the structural parameters of borehole(borehole inclination,depth,borehole diameter,etc.)are the main factors affecting the water inrush law of hydrophobic boreholes.According to the law that the dynamic change of borehole water inflow is in accord with exponential attenuation,and the transformation characteristics of groundwater flow pattern between aquifer and borehole,with COMSOL software as the simulation analysis platform,this paper presents the construction method of numerical analysis model of borehole water inrush in coal mining face,which generalizes the drained aquifer into infinite water-filled aquifer,uses finite element triangular tetrahedron division,generalizes borehole wall into Darcy seepage overflow boundary,and calculates borehole water inrush through real-time Darcy velocity integral in borehole wall area.Based on the single borehole drainage test of a coal mining face in Binchang Mining Area,Shaanxi Province,the simulation results show that when the borehole water inflow reaches a quasi-stable state,the groundwater head isosurface takes the borehole as the center and presents a"reverse funnel"state.The attenuation curve of borehole water inflow and the first-order single exponential attenuation mathematical model are fitted,the attenuation curve of the water inflow of the drainage borehole is basically consistent with the measured results,which are in accordance with the first-order single exponential attenuation mathematical model.In addition,the multi-scenario simulation studies the single borehole water inrush attenuation law under the conditions of different aquifer hydrogeological characteristics,and structural parameters.The results show that with the increase of initial water head and the permeability coefficient of aquifer,the peak water volume and seemingly stable water volume of boreholes increase linearly,but have little effect on the seemingly stable period of borehole water inflow.With the increase of elastic water supply coefficient of aquifer,the peak water volume of boreholes increases,and the seemingly stable water volume basically remains unchanged,but the seemingly stable period increases obviously,with the increase of borehole depth and borehole diameter,the peak value and quasi-steady water inflow of hydrophobic boreholes also increase.Moreover,the paper takes a computer workstation as hardware platform,and constructs a computer model of group boreholes interference drainage.The simulation results show that with the increase of the number of drainage boreholes and the coverage of the boreholes,the range of the water head is reduced obviously,and the water inrush capacity of the single hole and the drilling field decreases obviously,among which the water inrush capacity of the central hole in the drilling field is the mostly affected.