水力压裂技术广泛应用于煤矿坚硬顶板控制、冲击地压防治和低渗煤层增透等领域,而岩体水力压裂裂缝空间转向规律尚未完全厘清。为探究岩体水力裂缝空间转向扩展特征,采用三维数值模拟手段研究地应力、排量、流体黏度、天然裂缝、缝间诱导应力的影响效应。结果表明:裂缝转向主要发生在最大主应力法平面,随着中间主应力与最小主应力之差增加,裂缝朝中间主应力方向转向,且偏转程度逐渐加剧;提高排量或流体黏度将促使裂缝沿初始方向扩展;水力裂缝穿越天然裂缝呈绕道穿越和直接穿越两种典型模式,天然裂缝仅在局部范围内阻碍水力裂缝扩展,相交后水力裂缝仍沿最大主应力方向继续扩展。多条裂缝同时压裂时,裂缝易受诱导应力的干扰发生空间扭转,中间裂缝偏转程度最为剧烈;多条裂缝分段压裂时流体返排,诱导应力干扰效应显著降低。地应力场主导水力裂缝三维扩展方位,其他因素仅在局部范围内产生次级效应。研究结论可为煤矿井下水力压裂工程提供借鉴。

Hydraulic fracturing technology is widely used as an effective method for controlling hard roof,preventing rock burst and anti-reflection of low permeability coal seam. The three-dimensional non-plane propagation law     of hydraulic fracturing is not fully understood. In order to explore the three-dimensional non-planar propagation characteristics of hydraulic fractures in rock mass,the effects of in-situ stress,displacement,fluid viscosity,natural fractures and induced stress were evaluated using three-dimensional fluid-structure coupling numerical simulation method. The results show that the fracture redirection mainly occurs in the normal plane of maximum principal  stress. As the difference between intermediate and minimum principal stresses increases,the cracks turn towardsthe intermediate principal stress direction,and the deflection degree of cracks increases gradually. The propagation distance of hydraulic fractures along the initial direction gradually increases with the displacement or fluid   viscosity. There are two typical modes of hydraulic fracture crossing natural fractures:Bypass and direct crossing. Simultaneous fracturing of multiple fractures can result in spatial torsion due to the interference of induced stress,with the middle fracture experiencing the most significant deflection. The induced stress interference effect is significantly reduced as multiple fractures are fractured sequentially in stages. Stress field dominates the orientation of hydraulic fracture propagation,while other factors only produce secondary effects in local scope. This study provides insight into non-planar fracture propagation and the optimization of fracturing design and operation in coal mine.