通过水力压裂裂缝的诱导应力场打开远场天然裂缝，可改变储层应力场，易形成压裂主裂缝、分支缝、应力松弛缝相互连通的裂缝网络，从而提高了页岩气储层改造效率，因此在页岩气开采中具有广阔的应用前景。人工裂缝逼近条件下天然裂缝的破坏特征是人工裂缝诱导应力场激活远场天然裂缝的核心问题之一。应用位移间断法（DDM），建立了人工裂缝逼近条件下激活天然裂缝的力学模型。根据摩尔-库仑破坏准则，建立了不同天然裂缝破坏状态的约束条件，形成了天然裂缝破坏特征的计算方法，并通过算例验证其正确性。在此基础上，模拟了人工裂缝逼近条件下天然裂缝张开、滑移、闭合行为，并研究了其影响因素。结果表明，天然裂缝下表面处最大主应力呈双峰型分布，天然裂缝下表面处最大主拉应力随着天然裂缝与最大水平主应力方向夹角的增加而增大。当人工裂缝逼近天然裂缝时，天然裂缝的剪切型破坏长度大于张拉型。天然裂缝破坏长度随着天然裂缝与最大水平主应力方向夹角的增大而减小，随着缝内净压力的增大而增大。天然裂缝破坏长度随着人工裂缝尖端到天然裂缝的距离的减小而增加。天然裂缝剪切型破坏长度随着摩擦系数及黏聚力的增大而减小。研究结果对页岩气压裂技术具有理论指导意义。

Activation of the far-field natural fracture by stress field induced by the hydrofracture can change the rock stress field, reduce the difficulty in formation of interconnected fracture network, such as main, branch and stress relaxation fractures, and improve shale gas reservoir stimulation efficiency, and therefore, has broad prospects of application to the shale gas development. The failure characteristics of natural fractures in the vicinity of hydrofracture are one of the core issues to the activation of far-field natural fracture by stress field induced by the hydrofracture. Displacement discontinuity method (DDM) is used to construct a mechanical model for activation of natural closed fractures in the vicinity of hydrofracture. According to Mohr-Coulomb failure criteria, the constraint conditions in different natural fracture failure states are established; the calculation methods of natural fracture characteristics are formed; and the correctness of these calculation methods are verified by comparison with the existing calculation results of semi-analytical solution. On this basis, the opening, slipping and closing behaviors of natural fractures in the vicinity of hydrofracture are simulated; the natural fracture displacement discontinuity and maximum principal stress distribution characteristics under the action of stress field induced by the hydrofracture are analyzed; and the factors influencing natural fracture failure characteristics are studied. The research results show that the maximum principal stress at the backside surface of natural fracture is in bimodal distribution. As the angle between the natural fracture and the maximum horizontal principal stress increases; the maximum principal tensile stress increases. In the vicinity of hydrofracture, the tension-type failure length of natural fracture is less than its shear-type failure length. As the angle between the natural fracture and the maximum horizontal principal stress increases; the tension-type failure length and shear-type failure length of natural fracture decrease. The natural fracture failure length increases with the increase of net pressure and increases with the decrease of the distance from hydrofracture tip to natural fracture center. The shear-type failure length decreases with the increase of friction coefficient and cohesive force. The research results can provide theoretical guidance for shale gas fracturing technology.