Abstract Although the cohesive element method has been widely used for modeling hydraulic fracturing, the hardening properties of shear strength and shear fracture energy of rock matrix and natural fracture with the increasing of confining pressure have not been applied to the constitutive law of cohesive element for a long time. In this study, a shear hardening model and the corresponding user subroutine USDFLD are proposed and verified. Numerical results show that the shear hardening model has an excellent performance in modeling initial geo-stress state and shear hydraulic fracture (SHF) propagation in fractured reservoirs. The distribution and proportion of SHF affected by natural fracture asperity, azimuth of natural fracture network, and stress field are analyzed and discussed. The results suggest that SHF is a significant part of the hydraulic fracture network in fractured reservoirs with a proportion of 18%–61%, and plays a vital role in enhancing the complexity of hydraulic fracture network. The SHF has the potential to become the main type of the fracture network, indicating that its contribution in enhancing the conductivity of fractured reservoirs cannot be ignored. The macro width of the hydraulic fracture network and the tortuosity of the main hydraulic fracture decreases as asperity increases. High stress difference is a favorable stress environment for the development of SHF. As the absolute confining pressure of fractured reservoir increases, the possibility of shear hydraulic fractures becoming the primary fracture increases significantly.

中文翻译：

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粘性元法的剪切硬化模型及其在裂缝性油藏剪切水力压裂建模中的应用

摘要 虽然黏聚元法在水力压裂建模中得到了广泛的应用，但岩石基质和天然裂缝的抗剪强度和剪切断裂能随围压增加的硬化特性还没有应用于黏聚元的本构规律中。很久。在本研究中，提出并验证了剪切硬化模型和相应的用户子程序 USDFLD。数值结果表明，剪切硬化模型在模拟裂缝性储层中的初始地应力状态和剪切水力裂缝（SHF）扩展方面具有优异的性能。分析讨论了天然裂缝粗糙度、天然裂缝网络方位角、应力场对SHF的分布和比例的影响。结果表明，SHF是裂缝性油藏水力裂缝网络的重要组成部分，比例为18%～61%，对提高水力裂缝网络的复杂性起着至关重要的作用。SHF有潜力成为裂缝网络的主要类型，表明其对提高裂缝性储层导流能力的贡献不容忽视。水力裂缝网络的宏观宽度和主要水力裂缝的弯曲度随着粗糙度的增加而减小。高应力差是SHF发生的有利应力环境。随着裂缝性储层绝对围压的增加，剪切水力裂缝成为主要裂缝的可能性显着增加。