高位主关键层破断失稳及微震活动分析

Analysis of destabilized fracture and microseismic activity of high-located main key strata

基于板壳理论建立了两邻边固支、两邻边简支条件下高位主关键层的力学模型,利用瑞利-里兹法,推导出高位主关键层弯曲挠度函数的近似解析式和应力分布表达式,求解出高位主关键层破断跨度的计算式,并分析了该条件下的破断规律。根据现场微震监测,研究了高位主关键层破断运移与微震活动之间的关系。研究结果表明:该边界条件下主关键层破断前的最大挠度点靠近两简支边侧;主关键层破断失稳过程中,当破断前悬跨系数大于1时,主关键层沿倾向固支边上表面首先发生破断,当悬跨系数小于1时,主关键层沿走向固支边上表面首先发生破断,且主关键层破断跨度a与倾向悬露长度b的关系曲线呈W型。高位主关键层破断运移时诱发大能量微震事件,其破断步距和形式的分析结果与强微震活动规律相一致。

Based on the theory of plates and shells, a mechanical model is established for high-located main key strata with two clamped edges and two simply supported edges. With Rayleigh-Ritz method, an analytical expression of flexural function and an expression of stress distribution are derived for high-located main key strata. Thus, the formulation of fracture span for high-located main key strata is solved and then the fracture laws under the same condition are further analyzed. According to microseism monitoring, the dependence of the fracture at high-located main key strata on microseism activities is investigated. It is shown that the point of maximum deflection before the key strata fractured is located near two simply supported edges. During the destabilized fracture process of high-located main key strata, fracture initially occurs along the dip clamped edge when the spanning coefficient prior to fracture is higher than 1, whereas fracture firstly happens along the strike clamped edge when the coefficient is lower than 1. Moreover, the relation curve of fracture span a and dip suspension length b fits in W-shape. Finally, it is found that microseism activities with high energy result from the fractures and movement of high-located main key strata. Furthermore, the predicted fractured step and format are in good agreement with the monitored microseismic activities.