不同地应力条件下平行钻孔抽采瓦斯运移特性实验分析

利用自主研发的"多场耦合煤层气开采物理模拟实验系统",开展了不同地应力水平下平行钻孔瓦斯抽采的物理模拟实验,研究结果表明：1）平行钻孔瓦斯抽采中,抽采前期压降曲线斜率大,中、后期压降曲线斜率相对较小,并且相邻抽采管之间瓦斯解吸速率较边界抽采管快,任意时刻平行或垂直抽采管方向气压变化值均关于抽采管对称,离抽采管抽采段越近,瓦斯解吸速率越快,瓦斯解吸速率与距离抽采管连接段远近无关;2）瓦斯抽采中,随着地应力增加,瓦斯解吸速率减缓,压降漏斗收缩变小,瓦斯有效解吸面积变小,且地应力对消除突出危险区域出现时间影响差异不明显,但随着地应力增加,消突范围渐缩小;3）瓦斯抽采中,瞬时流量随时间演化可分为急速升高、快速衰减和极限抽采三个阶段,并且随着地应力增加,瞬时流量峰值减小,瞬时流量衰减速率减缓,瓦斯累积流量降低,累积流量增长速率减缓,抽采效率降低。

Experimental analysis on the characteristics of gas migration extracted by parallel boreholes under different stress conditions

With using the independently developed "multi-field coupling coalbed methane recovery physical simulation test system", physical simulation tests by parallel borehole gas drainage under different stress levels are carried out. The results are as follows:1) In parallel borehole gas extraction, the pressure drop curve slope in the early stage was large, while in the middle and late stage it was relatively small. The gas desorption rate between adjacent extraction pipes was faster than that of the boundary extraction pipe, and was parallel at any time. The change of pressure in the direction of vertical pumping pipe was symmetrical about the pumping pipe. The closer to the pumping stage of the pumping pipe, the faster the gas desorption rate, which was not related to the distance between the connection sections of the pumping pipe; 2) In the process of gas drainage, with stress increasing, gas desorption rate slowed down, pressure drop funnel shrank, and gas desorption area became smaller. Stress influenced the elimination of outburst hazardous areas, and the difference it brought about was not obvious at first, but with the increase of it, the scope of eliminating the conflict gradually decreased; 3) In the process of gas drainage, instantaneous flow rate evolution over time can be divided into three stages:rapid increase, rapid decay and limit extraction, and with the increase of stress, instantaneous flow peak value decreased, and its attenuation rate slowed down. The cumulative flow of gas was reduced, and its growth rate slowed down, resulting in reduction of extraction efficiency.