天然裂缝对煤层水力压裂裂缝扩展的影响

煤层井下水力压裂过程中，天然裂缝会对水压裂缝的扩展产生重要影响，通过建立水压压裂裂缝遇天然裂缝二维模型，采用理论分析结合数值模拟的方法，对裂缝扩展规律及天然裂缝破坏机理进行研究.研究表明:扩展中主裂缝与天然裂缝的相交角度、水平主应力差及天然裂缝的发育程度是影响扩展方向的主要因素.在低主应力差、低相交角的条件下，压裂裂缝趋于沿天然裂缝发生剪切破坏扩展;在高应力差和高相交角情况下，压裂裂缝易直接穿过天然裂缝扩展.当天然裂缝尺寸较长，压裂裂缝易沿天然裂缝扩展，而小尺寸的天然裂缝对裂缝扩展影响不大.

Effects of Natural Fractures on Hydraulic Fractures Propagation of Coal Seams

To investigate the effects of natural fractures on the hydraulic fracture propagation of underground coal seams， a two dimensional model of hydraulic fracture intersecting natural fractures was built， based on which， the laws of fracture propagation and the failure mechanisms of natural fractures were explored by applying theoretical analysis and numerical simulation. The research suggested that the angle of interaction， the horizontal differential principal stress and the development degree of natural fractures are the three main factors that affect the directions of fracture propagation. In the case of low horizontal differential principal stress and low angle of interaction， the propagation of hydraulic fractures is likely along the natural fractures due to shear failure; on the contrary， in the case of high horizontal differential principal stress and high angle of interaction， the propagating fracture is likely to cross the natural fractures. Small sized natural fractures have little or no effect on the directions of hydraulic fracture propagation whereas the propagating fractures move along the natural fractures when they are bigger in size.