高瓦斯煤层大直径钻孔卸压增透瓦斯渗流时空演化机理

Temporal and spatial evolution mechanism of large-diameter borehole pressure relief and permeable gas seepage in high gas coal seam

矿井瓦斯抽采面临抽采率低、有效抽采周期短、瓦斯预抽体积分数不达标等困境。为实现高瓦斯低透气性煤层的精准卸压增透,以顺和煤矿2404典型深井高瓦斯低透气性煤层工作面为研究对象,基于长时力学效应理论建模、COMSOL数值分析和现场试验等方法,构建了大直径钻孔卸压煤层瓦斯运移多场耦合模型,提出了大直径钻孔瓦斯有效抽采半径的判定指标——残余瓦斯压力不超过0.22 MPa,揭示了大直径煤层钻孔卸压增透机理及瓦斯运移规律:单一大直径钻孔煤层瓦斯压力呈以钻孔圆心为对称中心的椭圆分布,即由钻孔圆心向外瓦斯压力逐渐增加,随着抽采时间延长,抽采达标区域逐渐扩大。钻孔周边应力转移特征为:随着抽采时间增加,单一大直径钻孔周边点的垂直应力呈现先增后降趋势。进一步提出了高瓦斯低透气性煤层大直径钻孔卸压增透抽采技术。模拟确定了钻孔有效抽采半径,孔间距6.0 m、直径300 mm钻孔卸压增透效果最好,其两侧3.0 m内平均渗透率为1.58×10^(-15)m^(2),远大于初始值1.15×10^(-17)m^(2)。现场应用表明,大直径钻孔瓦斯抽采远优于普通钻孔,300 mm大直径钻孔瓦斯体积分数最大值为47.2%,75 mm原钻孔最大瓦斯体积分数最大值仅为10.6%,且大直径钻孔5.0%以上高瓦斯体积分数抽采天数提高了40.2%,有效解决了小直径瓦斯钻孔治理难题,为高瓦斯煤层高效精准卸压增透强化抽采提供了有效途径。

Mine gas extraction has the dilemma of low extraction rate,short effective extraction cycle,and substandard gas pre-extraction concentration.In order to realize the precise pressure relief and permeability of high gas and low gas permeability coal seam,taking the working face of high gas and low gas permeability coal seam in Shunhe Coal Mine 2404 as the research object,based on the methods of rheological theory modeling,COMSOL numerical analysis and field experiment,a multi-field coupling model of gas transport of large-diameter borehole pressure relief coal seam was constructed,and the determination index of the effective extraction radius of large-diamet-er borehole gas was proposed-the residual gas pressure did not exceed 0.22 MPa.The mechanism of pressure relief and permeability en-hancement,as well as the law of gas migration in large diameter coal seam drilling,are unveiled:the gas pressure within a single large dia-meter coal seam drilling exhibits an elliptical distribution with the center of the drilling circle serving as its symmetrical center.In other words,the gas pressure gradually increases from the center towards the outer edges of the drilling circle.Furthermore,with prolonged drainage time,there is a gradual expansion of the standard drainage area.The stress transfer around the borehole is characterized by the fact that with the increase of extraction time,the vertical stress of the peripheral points of a single large-diameter borehole shows a trend of first increasing and then decreasing,and the technology of high-gas and low-gas permeability coal seam large-diameter borehole pressure relief and enhanced penetration extraction is proposed.The simulation determined the effective extraction radius of the borehole,and the drilling hole with a hole spacing of 6.0 m and a diameter of 300 mm had the best pressure relief and penetration enhancement effect,and the average permeability within 3.0 m on both sides was 1.58×10^(-15) m^(2),which was much greater than the initial value of 1.15×10^(-17) m^(2).The field application demonstrates that gas extraction in a large diameter borehole is significantly superior to that in an ordinary borehole.In a 300 mm large diameter borehole,the maximum gas volume fraction reaches 47.2%,whereas it only amounts to 10.6%in a 75 mm original borehole.Furthermore,the extraction duration of high gas volume fraction increases by 40.2%in the large diameter borehole.This ap-proach effectively addresses the challenge of controlling small diameter gas boreholes and provides an efficient method for precise pres-sure relief and permeability enhancement of high gas coal seams.