Anisotropic characteristics of the energy index during the shale failure process under triaxial compression
Anisotropic characteristics of the energy index during the shale failure process under triaxial compression
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三轴压缩下页岩破坏过程能量指数各向异性特征
DOI：
10.1016/j.jngse.2021.104219
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发表时间：
2021-08-31
影响因子：
--
通讯作者：
Li, Cunbao
中科院分区：
文献类型：
--
作者：
Hu, Jianjun;Gao, Chao;Li, Cunbao
能量转换是泥页岩各向异性变形、损伤形成和演化的重要驱动力。本文首次在考虑泥页岩固有各向异性的情况下，对泥页岩破坏过程中的5个能量指标（总输入能量U-t、可释放能量U-e、耗散能量U-d、剪切能量U-V和畸变能量U-D）进行了详细的理论计算。系统地讨论了五个能量指标的各向异性特征。结果表明，层理结构对这些能量指标有较大影响。U-e、U-V和U-D均在层理方位为60 °时减小到最小值，然后随着层理程度的增加而增大。U-e、U-V和U-D与围压的关系可用线性函数描述，类似于抗压强度随岩层倾角或围压的变化。随着轴向应变的增加，U-e，U-V和U-D的增加率首先增加，然后保持不变，然后在破坏前下降;然而，U-t和U-d的增加率继续增加，直到破坏。U-e、U-D和U-V与峰值抗压强度有较强的相关性，而与峰值轴向应变的相关性较弱，而U-t和U-d与峰值强度和峰值应变的相关性则相反。能量指标的各向异性特征有助于进一步阐明泥页岩的破坏机理，对水力压裂设计具有重要意义。
Energy conversion is an essential driving force of shale anisotropic deformation, damage initiation and evolution. In this study, theoretical calculations of five energy indexes (total input energy U-t, releasable energy U-e, dissipated energy U-d, dilatational energy U-V and distortional energy U-D) during the shale failure process considering the inherent anisotropy of shale are presented in detail for the first time. The anisotropic features of the five energy indexes are systematically discussed. The results indicate that bedding structure considerably influences these energy indexes. U-e, U-V and U-D all decrease to a minimum as the bedding orientation reaches 60 degrees and then increase with the bedding degree. The relationships between U-e, U-V and U-D and the confining pressure can be described by linear functions, similar to the variation in the compressive strength with either bedding inclination angle or confining pressure. As the axial strain increases, the rates of increase in U-e, U-V and U-D first increase, then remain constant, and then decrease before failure; however, the rates of increase in U-t and U-d continue to increase until failure. U-e, U-D and U-V have strong relationships with the peak compressive strength but weak relationships with the peak axial strain, whereas U-t and U-d exhibit the opposite relationships with the peak strength and strain. The anisotropic characteristics of the energy indexes can help to further elucidate the failure mechanisms of shale and are of great significance to hydraulic fracturing design.