正断层影响下顺层钻孔有效抽采半径研究

Study on effective extraction radius of bedding borehole under the impact of normal fault

合理的钻孔有效抽采半径是保证瓦斯抽采效果的关键。但目前对钻孔有效抽采半径的研究主要集中在测定方法方面,缺乏对正断层特殊地质条件下的钻孔有效抽采半径研究。以贵州某矿采煤工作面为工程背景,构建流固耦合模型,采用数值模拟与钻孔抽采瓦斯量法相互验证的方式分析了无断层影响下顺层钻孔有效抽采半径变化规律,结果表明:瓦斯抽采120 d时,有效抽采半径数值模拟结果为3.10 m,现场试验结果为2.93 m,现场试验结果与数值模拟结果基本一致,验证了流固耦合模型的可靠性。利用多物理场耦合仿真软件分析了正断层影响下顺层钻孔有效抽采半径的变化规律,结果表明:在一定抽采时间范围内,钻孔距正断层一定距离时,瓦斯压力曲线会出现驼峰状分布,且峰值间隔约为3.5 m;正断层附近钻孔有效抽采半径随距断层距离的增大而增大,正断层对钻孔有效抽采半径的影响范围在距断层70 m内。结合正断层影响下的分析结果,在保证抽采效果和不延长抽采时间的前提下,对正断层附近瓦斯抽采钻孔布孔间距实施分段布置:在靠近断层30 m内密集布置钻孔,布孔间距应不大于距断层10 m时的有效抽采半径(1.83 m);在距断层30~70 m范围内,在保证安全的情况下,可适当加大钻孔的布孔间距;在距断层70 m外,可逐步恢复至无正断层影响下顺层钻孔的布孔间距。

The reasonable effective extraction radius of borehole is the key to ensure gas extraction effect.However,the research of effective extraction radius mainly focuses on the measurement method of effective extraction radius of borehole,and there is a lack of research on the effective extraction radius of borehole under special geological conditions of normal fault.Taking a coal working face in Guizhou as the engineering background,the fluid-solid coupling model is established,and the variation law of effective extraction radius of bedding borehole without fault impact is analyzed by means of mutual verification between numerical simulation and borehole gas extraction method.The results show that when the gas is extracted for 120 days,the effective extraction radius of the numerical simulation is 3.10 m,and that of the field test is 2.93 m.The field results are basically consistent with the numerical simulation results,which verifies the reliability of the fluid-solid coupling model.By using multi-physics field coupling simulation software,the variation law of effective extraction radius of bedding borehole under the impact of normal fault is analyzed.The results show that within a certain extraction time range,when the borehole is at a certain distance from the normal fault,the gas pressure curve will have a hump-like distribution,and the peak interval is about 3.5 m.The effective extraction radius of the borehole near the normal fault increases with the increase of the distance from the fault.The impact of the normal fault on the effective extraction radius of the borehole is within 70 m from the fault.Combined with the analysis results under the impact of normal faults,the spacing of gas drainage boreholes near the normal fault is arranged in sections under the premise of ensuring the extraction effect and not prolonging the extraction time.Within 30 m from the fault,the boreholes are densely arranged,and the spacing between the boreholes should not be greater than the effective extraction radius(1.83 m)when the distance from the fault is 10 m.Within the range of 30-70 m from the fault,under the condition of ensuring safety,the spacing of boreholes can be appropriately increased.After 70 m from the fault,the spacing can be gradually restored to the borehole spacing layout of bedding boreholes without the impact of the normal fault.