Anisotropic microscale failure mechanism of shale

IF 5.6 1区 工程技术 Q1 ENGINEERING, GEOLOGICAL Acta Geotechnica Pub Date : 2024-06-21 DOI:10.1007/s11440-024-02353-5
Lei Deng, Lingzhi Xie, Bo He, Yao Zhang, Jun Liu, Peng Zhao
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Abstract

As a hydrocarbon reservoir rock, shale is generally composed of highly compacted clay particles with submicrometer sizes and includes nanometric porosity and different hard particles, like quartz, pyrite, etc. One of the key reasons for the formation of a complex fracture network via hydraulic fracturing is the multiscale heterogeneity of shale, especially heterogeneity on the microscale. This paper conducted on an experimental investigation of shale and explored the intrinsic relationship between the microstructure, the related mechanical properties at the micrometer level and the anisotropic failure mechanism. Small-scale specimens with micrometer dimensions in the form of cantilever beams with rectangular cross-section were fabricated by means of a focused ion beam (FIB) and tested via bending with a nanoindenter. The load–deflection curves of these bending beams were monitored up to failure, and the tensile strength of the shale composite was directly derived from the load–deflection curves at 474.5 MPa (parallel to the bedding plane) and 168.9 MPa (vertical to the bedding plane). The results show that the strength anisotropy of shale at the micrometer scale is driven by the clay particles and other minerals, and the bonds of these particles. The modulus anisotropy of the shale composite at the microscale is dominated by the orientation of clay particles. Moreover, the shale composite embedded with pyrite exhibited strong softening characteristics.

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页岩的各向异性微尺度破坏机制
作为一种碳氢化合物储层岩石,页岩一般由亚微米级的高致密粘土颗粒组成,包括纳米级孔隙度和不同的硬质颗粒,如石英、黄铁矿等。通过水力压裂形成复杂压裂网络的关键原因之一是页岩的多尺度异质性,尤其是微尺度异质性。本文对页岩进行了实验研究,探讨了微观结构、微米级相关力学性能与各向异性破坏机制之间的内在联系。利用聚焦离子束(FIB)制作了微米级的矩形截面悬臂梁小尺寸试样,并用纳米压头进行了弯曲测试。对这些弯曲梁的载荷-挠度曲线进行了监测,直至其失效,并根据载荷-挠度曲线直接推导出页岩复合材料在 474.5 兆帕(平行于垫层平面)和 168.9 兆帕(垂直于垫层平面)时的抗拉强度。结果表明,页岩在微米尺度上的强度各向异性是由粘土颗粒和其他矿物质以及这些颗粒之间的粘结所驱动的。页岩复合材料在微米尺度上的模量各向异性主要受粘土颗粒取向的影响。此外,嵌入黄铁矿的页岩复合材料表现出很强的软化特性。
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来源期刊
Acta Geotechnica
Acta Geotechnica ENGINEERING, GEOLOGICAL-
CiteScore
9.90
自引率
17.50%
发文量
297
审稿时长
4 months
期刊介绍: Acta Geotechnica is an international journal devoted to the publication and dissemination of basic and applied research in geoengineering – an interdisciplinary field dealing with geomaterials such as soils and rocks. Coverage emphasizes the interplay between geomechanical models and their engineering applications. The journal presents original research papers on fundamental concepts in geomechanics and their novel applications in geoengineering based on experimental, analytical and/or numerical approaches. The main purpose of the journal is to foster understanding of the fundamental mechanisms behind the phenomena and processes in geomaterials, from kilometer-scale problems as they occur in geoscience, and down to the nano-scale, with their potential impact on geoengineering. The journal strives to report and archive progress in the field in a timely manner, presenting research papers, review articles, short notes and letters to the editors.
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