瓦斯抽采是目前国内煤矿瓦斯治理的主要方法，瓦斯抽采具有安全性高、提高瓦斯回收再利用等优势。但在瓦斯抽采过程中，由于成孔过程会导致地应力分布的改变，引起瓦斯抽采钻孔出现不同程度的变形失稳，导致瓦斯抽采效率下降。因此本文基于岩石力学和流体力学等相关理论，采用理论分析、物理相似模拟实验和数值模拟等研究方法，系统研究了钻孔不同位置出现不同程度的变形失稳对瓦斯抽采效果的影响及变化规律。

基于钻孔内瓦斯流动理论获得了钻孔变形失稳条件下钻孔内瓦斯抽采的负压损失规律。分析得到了当钻孔出现变形失稳后抽采负压损失的分布特征，完整孔抽采压力损失总体不大，随着抽采时间延长，由于抽采流量的持续衰减，钻孔抽采过程中压力损失幅度逐渐降低。随着钻孔塌孔程度增加，有效抽采断面的逐步减小，抽采压力在钻孔中的损失越来越大，瓦斯抽采效果将越来越差。

通过开展不同的抽采负压条件下钻孔不同位置出现不同程度的塌孔的物理相似模拟实验，获得抽采负压和抽采流量在钻孔轴向方向上的变化规律。结果表明当钻孔完整时，钻孔内负压损失较小，抽采流量沿钻孔长度呈线性分布。当钻孔出现塌孔时，抽采负压损失增加，塌孔程度越大负压损失越大，孔底塌孔50%时负压损失由1.87 kPa增加至2.74 kPa，孔底塌孔80%时负压损失由2.83 kPa增加至4.12 kPa。钻孔孔底出现堵孔情况时，由于完整孔与堵孔段无法形成有效通路，堵孔段内垮落煤体与钻孔周围煤体相接触形成连续的煤体，堵孔段的瓦斯流动由管道流转变为渗流。

运用COMSOL数值模拟软件以蒋家河煤矿ZF219工作面为参照，并根据煤层实际参数，模拟了钻孔不同位置和不同程度的塌孔对钻孔内瓦斯抽采负压、抽采流量和煤层瓦斯压力变化情况。认为当钻孔孔口出现塌孔时，对钻孔的抽采流量影响最大。钻孔周围瓦斯压力除塌孔位置外会随着时间的推移出现不同程度的变化，未发生塌孔处与完整孔区别不大。

通过设计现场对比试验在蒋家河煤矿ZF219工作面进行，设置三个钻孔，在抽采35 d后钻孔抽采流量出现降低，通过内窥镜观测钻孔内部发现钻孔出现塌孔，对两个试验钻孔分别进行水力冲孔和调整负压影响其抽采效果。由于调整抽采负压未解决钻孔内的塌孔情况，因此调整负压对改善钻孔变形失稳而引起的瓦斯抽采效果的降低不如进行水力冲孔。

Gas extraction is the main method of gas control in domestic coal mines at present. Gas extraction has the advantages of high safety and improving gas recovery and reuse. However, in the process of gas extraction, due to the change of in-situ stress distribution caused by the process of hole formation, there are different degrees of deformation and instability in the gas extraction borehole, resulting in the reduction of gas extraction efficiency. Therefore, based on the related theories of rock mechanics and fluid mechanics, this paper adopts the research methods of theoretical analysis, physical similarity simulation experiment and numerical simulation, the influence of different degree of deformation and instability in different position of borehole on gas drainage and its variation law are systematically studied.

Through the theory of gas flow in the borehole, the negative pressure loss of gas drainage in the borehole is calculated when the borehole is deformed and unstable. The distribution of negative pressure is obtained when the borehole is deformed and unstable, and the pressure loss of complete borehole is small as a whole, and with the increase of extraction time, because of the decrease of extraction flow, the pressure loss of borehole pumping is also gradually reduced. With the gradual severity of borehole collapse, the effective extraction section of borehole becomes smaller and smaller, the pressure loss in borehole increases, and the effect of gas extraction becomes worse and worse.

Based on the physical similarity simulation experiment of borehole collapse at different positions under different negative pressure conditions, the variation law of negative pressure and pumping flow in the axial direction of borehole is obtained. The results show that when the borehole is complete, the negative pressure loss in the borehole is small, and the pumping flow has a linear distribution along the length of the borehole. When the borehole collapse occurs, the negative pressure loss increases, the greater the degree of hole collapse, the greater the negative pressure loss, 50% hole collapse at the bottom of the hole from 1.87 kPa to 2.74 kPa, the negative pressure loss increases from 2.83 kPa to 4.12 kPa when the hole bottom collapses 80%. When the hole is blocked at the bottom of the borehole, because the complete hole can not form an effective passage with the blocked section, the coal in the blocked section contacts with the coal around the borehole to form a continuous coal body, the gas flow in the plugging section changes from pipe flow to percolation flow.

Based on the practical data of ZF219 coalface at Jiang Jiahe Colliery by COMSOL, the variation of minus pressure, drainage flow and coal seam gas pressure in different locations and degrees of borehole collapse were simulated. The results show that when the borehole collapse occurs, the influence on the pumping flow rate is the greatest, and when the borehole.The gas pressure around the borehole will change with time in different degrees except for the location of collapse hole.

The design field contrast experiment was carried out in the ZF219 working face of Jiangjiahe coal mine, three boreholes were set up, after 35 days of pumping, the discharge of the borehole decreased, the borehole collapsed was found through the observation of the bore through the endoscope, the effect of pumping was influenced by hydraulic punching and adjusting negative pressure in the two experimental boreholes respectively. Because adjusting negative pressure can not solve the problem of hole collapse, it is better to reduce the effect of gas extraction by hydraulic punching than by adjusting negative pressure.