人为弱面对坚硬难垮顶板水力压裂的影响研究

弱面对水压裂隙的扩展有着重要影响,为达到有效控制坚硬难跨顶板,需要研究人为弱面对水力压裂的影响。根据水压裂隙产生及扩展机理,运用数值模拟试验方法,通过声发射及剪应力分布研究了3种人为弱面影响下的水力压裂过程中裂隙扩展特征,对比分析了 7种压裂方式下的水力压裂数据。结果表明:预制裂隙开挖形成的层理弱面和监测孔开挖形成的应力卸压圈均能影响水压裂隙的扩展,在扩展方向上水压裂隙往往偏向于高孔隙水压力的区域扩展,且其在扩展一段之后受顶板自由面影响,主裂隙向工作面两端延伸4.5~8.5倍孔径的区域时会发生近90°的空间转向。水力压裂数据研究表明,预制裂隙和监测孔协同作用强化了控制坚硬难垮顶板的效果。

Effect of Man-Made Weak Plane on Hydraulic Fracturing of Hard and Stable Roof

Weak plane has an important influence on fracture propagation. It is necessary to study the effect of man-made weak plane on hydraulic fracturing in order to achieve the goal of controlling the hard and stable roof. According to the production and propagation mechanism of hydraulic fracturing, the numerical experiments are adopted and the crack extension features during the process of hydraulic fracturing under the effect of three kinds of man-made weak plane are studied through the distribution of acoustic emission and shear stress. The data of hydraulic fracturing are contrastively analyzed under seven kinds of fracturing method. The results show: the weak bedding face formed by excavation of the prefabricated crack and the unloading stress circle both can affect the crack extension of hydraulic fracture. Hydraulic fracturing are prone to extend to the region of high pore water pressure in the direction of extension. Due to the effect of roof surface after a period of extension, The main fractures will happen with 90° turn in the spatial when it extends to the ends of the face which is in the 4.5 ~ 8.5 times of the area of aperture. The data of hydraulic fracturing show that the synergistic effect of prefabricated crack and monitoring hole can strengthen the control of hard and stable roof.