To clarify the influence of pore pressure gradient on hydraulic fracture propagation, the stress distribution in and around the borehole is explained by theoretical analysis method in this paper. A mechanical model of hydraulic fracture initiation under the action of pore pressure gradient is established. Then coupled seepage-stress-damage software is used to simulate the initiation and propagation of hydraulic fractures in rock samples under the action of pore pressure gradient. Finally, the influence of the number and spatial position of the induction holes on the initiation and propagation of hydraulic fractures is analyzed. It is shown that: (1) Pore pressure gradient can effectively reduce the initiation pressure of hydraulic fractures. (2) The greater the pore pressure gradient is, the easier the hydraulic fracture is to spread to the region with high pore pressure. (3) With the action of pore pressure gradient, the hydraulic fracture is shaped as ‘丨’, ‘丿’ and ‘S’ types and can be represented by the four abstract conceptual models.

为了阐明孔隙压力梯度对水力压裂扩展的影响，本文通过理论分析方法解释了井眼内部和周围的应力分布。建立了孔隙压力梯度作用下水力压裂起始的力学模型。然后使用耦合的渗流-应力-破坏软件模拟孔隙压力梯度作用下岩石样品中水力压裂的萌生和扩展。最后，分析了感应孔的数量和空间位置对水力压裂的产生和传播的影响。结果表明：（1）孔隙压力梯度可以有效降低水力压裂的初始压力。（2）孔隙压力梯度越大，水力压裂越容易扩散到孔隙压力高的区域。（3）在孔隙压力梯度的作用下，水力压裂的形状为“丨”，“丿”和“ S”型，可以用四个抽象的概念模型来表示。