Abstract The physical, mechanical, and hydraulic properties of shales with continuous bedding plane vary with bedding orientation significantly. Thus, understanding and predicting crack initiation and propagation in hydraulic fracturing of bedded shale are crucial in terms of reservoir reconstruction. In this paper, a hybrid phase‐field method is proposed to investigate the hydraulic fracturing behaviour in bedded shale with pre-existing crack subjected to fluid injection. First, the Terzaghi and Mandel problems are carried out to validate the fully coupled hydro-mechanical model. The hybrid phase-field model applying to hydraulic fracturing treatment in the porous media is validated by the experiment of the plaster with a circular hole and two symmetric pre-existing cracks subjected to internal pressurization. Then, the numerical investigations of hydraulic fracturing behaviour in bedded shale specimen containing prefabricated cracks and varying bedding angles are implemented by employing the hybrid phase-field model. Moreover, the fluid pressure, damage region area and injection time responses are numerically investigated. Finally, the interaction of hydraulic fractures and two pre-existing natural cracks in bedded shale is presented. The hybrid phase-field modeling results show that the crack propagation paths and fluid pressure of bedded shale specimens depend on the pre-existing crack configuration, bedding angle and the mechanical and seepage properties of the bedding plane.

中文翻译：

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层状页岩水力压裂裂纹萌生与扩展的混合相场模型研究

摘要 具有连续层理面的页岩的物理、力学和水力性质随层理取向而显着变化。因此，了解和预测层状页岩水力压裂裂缝的萌生和扩展对于储层改造至关重要。在本文中，提出了一种混合相场方法来研究在流体注入作用下具有预先存在裂缝的层状页岩的水力压裂行为。首先，通过 Terzaghi 和 Mandel 问题来验证完全耦合的水力机械模型。通过对具有圆孔和两个对称预存裂缝的石膏进行内加压试验，验证了适用于多孔介质中水力压裂处理的混合相场模型。然后，采用混合相场模型对包含预制裂缝和不同层理角度的层状页岩试样的水力压裂行为进行了数值研究。此外，对流体压力、损伤区域面积和注入时间响应进行了数值研究。最后，介绍了水力裂缝和层状页岩中两个预先存在的天然裂缝的相互作用。混合相场建模结果表明，层状页岩试样的裂缝扩展路径和流体压力取决于预先存在的裂缝配置、层理角度以及层理面的力学和渗流特性。此外，对流体压力、损伤区域面积和注入时间响应进行了数值研究。最后，介绍了水力裂缝和层状页岩中两个预先存在的天然裂缝的相互作用。混合相场建模结果表明，层状页岩试样的裂缝扩展路径和流体压力取决于预先存在的裂缝配置、层理角度以及层理面的力学和渗流特性。此外，对流体压力、损伤区域面积和注入时间响应进行了数值研究。最后，介绍了水力裂缝和层状页岩中两个预先存在的天然裂缝的相互作用。混合相场建模结果表明，层状页岩试样的裂缝扩展路径和流体压力取决于预先存在的裂缝配置、层理角度以及层理面的力学和渗流特性。