井下超长水平孔分段压裂防冲机理及效果
Mechanism and effect of rock burst prevention using overlength horizontal hole staged fracturing technology
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摘要: 坚硬厚层顶板是冲击地压的主要影响和诱发因素之一,针对冲击地压煤层上方高位厚硬顶 板难以实现大范围卸压的难题,开发了井下超长水平孔分段压裂防冲技术。 采用 CDEM 数值模拟 方法分析了超长水平孔分段压裂弱化厚硬顶板的卸压防冲效果,结果表明:压裂后高位厚硬顶板垮 落更充分,来压步距更短,来压强度更低,同时工作面超前支承压力和巷道侧向支承压力也明显降 低。 提出了井下超长水平孔分段压裂卸压减冲原理,即通过对具有冲击致灾性的厚硬顶板实施大 范围水力压裂,使完整性好的目标岩层形成数量众多、方位和长度不一的网状裂缝,从而大幅减弱 岩层的整体强度,使上覆岩层的垂直应力由“硬传递”转化为“软传递”,降低了压裂区域下方煤层 的整体静载水平;其次,压裂后坚硬顶板能及时垮落并充填采空区,减小了顶板来压产生的集中动 载,使动载效应减弱,冲击风险降低。 使用该技术在强冲击危险工作面进行了试验研究,结果表明, 压裂期间,水压曲线在裂缝延伸压力区间内呈锯齿形波动,稳定时间长,表明裂缝扩展持续充分;在 实施压裂的区域,微震事件由工作面前方向工作面后方和未压裂区转移,同时高能微震事件明显降 低、低能微震事件增加,丛集效应弱化,开采扰动范围和顶板活动强度也有明显减小,巷道冲击风险 显著降低,工作面最终实现了安全回采。Abstract: Aiming at the problem that it is difficult to achieve a large⁃scale treatment of high⁃level thick and hard roof in rockburst coal seams,a super⁃long horizontal hole segmented fracturing anti⁃scouring technology is proposed. The CDEM numerical simulation method is used to analyze the rock burst prevention and pressure relief effect of over⁃ length horizontal hole staged fracturing for weakening thick and hard roof. The simulation shows that the roof collapse is more sufficient,the weighting step is shorter,the weighting strength is lower,and the advance abutment pressure of working face and lateral abutment pressure of roadway are also significantly reduced after fracturing,so the pressure relief effect is obvious. The principle of roof regional fracturing to reduce rock burst is put forward,that is,by greatly re⁃ ducing the overall strength of the strata, the stress of the strata above the coal seam is transformed from “ hard transfer” to “soft transfer”,so as to reduce the overall static load level of the mining coal seam. At the same time,the weakened thick and hard roof can collapse and fill the goaf in time during the mining process,so as to reduce the dy⁃ namic load of the roof. By simultaneously reducing the dynamic and static loads causing the rock burst initiation,the peak stress area of the roadway is always below the critical stress value of the rock burst,which can significantly re⁃ duce or even eliminate the hidden danger caused by the rock burst of thick and hard roof. The field engineering prac⁃ tice shows that the pressure curve fluctuates zigzag in a stable range,indicating that the fracture development is contin⁃ uous and sufficient during fracturing. In the fracturing area,the frequency of high⁃energy microseismic events is signifi⁃ cantly reduced,the low⁃energy events are increased,the clustering effect is weakened,and the mining disturbance range and intensity are also significantly reduced. Finally,the safe mining of working face is realized,and the effect of pressure relief to prevent rock burst is remarkable.