煤矿坚硬顶板分段水力压裂防冲效果监测与评价

Monitoring and evaluation of segmented hydraulic fracturing effect in rock burst prevention on hard roof of coal mine

针对坚硬顶板易形成悬顶导致应力集中及大面积悬顶突然破断形成动载扰动并诱发冲击动力灾害等问题,以东滩煤矿6303工作面为研究背景,提出定向长钻孔分段水力压裂区域坚硬顶板治理技术。在顶板关键层共布置4个钻孔,钻孔长度最深达792 m,累计完成28段压裂。为评价顶板致裂效果,利用光纤光栅三维应力长期动态监测系统和SOS微震系统对水力压裂前后三维采动应力和微震事件进行实时监测。研究结果表明:定向长钻孔分段水力压裂实施后,顶板岩层应力集中程度明显降低,主应力方向改变,超前支承压力影响范围减小,采动影响下应力集中系数由2.20下降到1.32,弹性应变能密度峰值由200 kJ/m^(3)下降到80 kJ/m^(3);压裂后大能量微震事件明显减少,微震事件日平均能量由100 kJ/d下降到10 kJ/d,能量释放缓和且均匀,空间平均释放能量保持在4~8 kJ/m,且由低频高能释放形式转变为高频低能释放形式。

Aiming at the problems of stress concentration and dynamic load disturbance induced by hard roof,the segmented hydraulic fracturing technology with directional long boreholes was used in the key roof layer above the coal seam in the 6303 working face of Dongtan Mine.A total of 4 boreholes were arranged,with the maximum length of 792 m,and 28 fracturing sections were completed.The three-dimensional stress monitoring system and the SOS microseismic system were used to realize real-time monitoring of the three dimensional mining stress and microseismic events before and after hydraulic fracturing,so as to evaluate the fracturing effect.The results show that after fracturing,the stress concentration of the roof rock layer is significantly reduced,the direction of the principal stress changes,the influence range of the leading abutment pressure is reduced,the stress concentration factor drops from 2.20 to 1.32 under the influence of mining,and the peak elastic strain energy density decreases from 200 kJ/m^(3)to below 80 kJ/m^(3).The number of high-energy microseismic events is significantly reduced,the daily average energy of the microseismic events decreases from 100 kJ/d to 10 kJ/d,and the spatial average energy release remains at 4~8 kJ/m.The energy release mode changes from low-frequency and high-energy microseismic events to high-frequency and low-energy microseismic events.