The fracture initiation behavior for hydraulic fracturing treatments highlighted the necessity of proposing fracture criteria that precisely predict the fracture initiation type and location during the hydraulic fracturing process. In the present study, a Mohr-Coulomb criterion with a tensile cut-off is incorporated into the finite element code to determine the fracture initiation type and location during the hydraulic fracturing process. This fracture criterion considers the effect of fracture inclination angle, the internal friction angle and the loading conditions on the distribution of stress field around the fracture tip. The results indicate that the internal friction angle resists the shear fracture initiation. Moreover, as the internal friction angle increases, greater external loads are required to maintain the hydraulic fracture extension. Due to the increased pressure of the injected water, the tensile fracture ultimately determines the fracture initiation type. However, the shear fracture preferentially occurs as the stress anisotropy coefficient increases. Both the maximum tensile stress and equivalent maximum shear stress decrease as the stress anisotropy coefficient increases, which indicates that the greater the stress anisotropy coefficient, the higher the external loading required to propagate a new fracture. The numerical results obtained in this paper provide theoretical supports for establishing basis on investigating of the hydraulic fracturing characteristics under different conditions.

水力压裂治疗的裂缝起裂行为凸显了提出裂缝准则的必要性，该准则可精确预测水力压裂过程中的裂缝起裂类型和位置。在本研究中，将具有拉力截止值的Mohr-Coulomb准则合并到有限元代码中，以确定水力压裂过程中的裂缝起始类型和位置。该断裂准则考虑了断裂倾角，内摩擦角和载荷条件对断裂尖端周围应力场分布的影响。结果表明，内摩擦角可抵抗剪切断裂的产生。而且，随着内摩擦角的增加，需要更大的外部载荷来维持液压裂缝的延伸。由于注入水的压力增加，拉伸断裂最终决定了断裂的起始类型。但是，随着应力各向异性系数的增加，剪切断裂优先发生。最大拉伸应力和等效最大剪切应力都随应力各向异性系数的增加而减小，这表明应力各向异性系数越大，传播新裂缝所需的外部载荷越高。本文获得的数值结果为研究不同条件下的水力压裂特征提供了理论依据。拉伸断裂最终决定了断裂的起始类型。但是，随着应力各向异性系数的增加，剪切断裂优先发生。最大拉伸应力和等效最大剪切应力都随着应力各向异性系数的增加而减小，这表明应力各向异性系数越大，传播新裂缝所需的外部载荷就越高。本文获得的数值结果为不同条件下水力压裂特征的研究奠定了理论基础。拉伸断裂最终决定了断裂的起始类型。但是，随着应力各向异性系数的增加，剪切断裂优先发生。最大拉伸应力和等效最大剪切应力都随着应力各向异性系数的增加而减小，这表明应力各向异性系数越大，传播新裂缝所需的外部载荷就越高。本文获得的数值结果为研究不同条件下的水力压裂特征提供了理论依据。最大拉伸应力和等效最大剪切应力都随着应力各向异性系数的增加而减小，这表明应力各向异性系数越大，传播新裂缝所需的外部载荷就越高。本文获得的数值结果为研究不同条件下的水力压裂特征提供了理论依据。最大拉伸应力和等效最大剪切应力都随应力各向异性系数的增加而减小，这表明应力各向异性系数越大，传播新裂缝所需的外部载荷越高。本文获得的数值结果为不同条件下水力压裂特征的研究奠定了理论基础。