基于微震监测的覆岩裂隙演化规律相似模拟试验研究

Similar material simulation test study on evolution law of overburden fracture based on microseismic monitoring

为研究“三软”煤层覆岩裂隙演化规律,采用物理模拟试验,结合微震监测仪器、压力传感器,研究回采工作面微震事件的分布特征及其与底板压力变化规律之间的关系,分析了覆岩裂隙演化特征。研究表明:模型回采期间总共发生9次周期来压,来压步距有明显的一大一小规律,第6次来压之后空洞闭合,断裂带不再向上发育,此后断裂带随着回采只发生横向的变化;开采过程中覆岩裂隙演化是一个复杂的能量释放过程,在回采初期至第4次周期来压期间微震事件频次和能量都在增加并在第4次来压之后到达峰值,而在第6次来压之后空洞闭合,纵向破断裂隙基本停止向上发展,此后微震事件频次和能量都在减小;底板压力的变化规律和微震事件能量频次的变化规律基本一致,但是压力数据变化的分区更加明显且具有滞后性,微震事件波动范围大于压力的波动范围;裂隙密度的变化与微震事件能量频次的变化都存在一个先增大后减小的过程,但是2种变化在增大过程中的协同变化现象要大于减小过程中的这一现象。由模拟结果和现场钻孔窥视监测确定出了上覆岩层的瓦斯富集区域,根据这一研究成果布置高位钻孔抽采瓦斯后,工作面采动断裂带、上隅角高瓦斯浓度区域的瓦斯富集得到了较好的控制,保证了工作面的安全高效生产。

In order to study the evolution law of overburden fracture in the“three-soft”coal seams,physical simulation experiments were used,combined with microseismic monitoring instruments and pressure sensors,to study the distribution characteristics of the microseismic events in the mining face and their relationship with the variation law of floor pressure,and the overburden characteristics of fissure evolution were analyzed.The research shows that:during the recovery of the model,a total of nine times of periodic pressure oc⁃curred,and the step distance has obvious pattern of large and small.After the sixth pressure,the cavity was closed and the fracture zone no longer developed upward.After that,the fracture zone only occurred laterally with the recovery;the evolution of overburden cracks dur⁃ing mining was a complex energy release process.The frequency and energy of microseismic events increase from the initial mining stage to the fourth cycle of pressure,and reach the peak value after the fourth pressure.After the sixth pressure onset,the cavity was closed and and the vertical fracture gap basically stopped to develop upward.After that,the frequency and energy of microseismic events decreased;the variation law of floor pressure and the variation law of energy frequency of microseismic events were basically the same,but the pres⁃sure data changed.The zoning is more obvious and has hysteresis,and the fluctuation range of microseismic events is larger than the fluc⁃tuation range of pressure;Both the change of fracture density and the change of energy frequency of microseismic events increase first and then decrease.But the two changes are in the process of increasing.Based on the simulation results and on-site drilling and peep monito⁃ring,the gas enrichment area of the overlying strata was determined.According to this research result,the high-level boreholes were ar⁃ranged for gas drainage.The gas enrichment has been well controlled,ensuring the safe and efficient production of the working face.