Understanding the changes in the mechanical properties of shale exposed to fracturing fluids is crucial for optimizing parameters in hydraulic fracturing. However, the dynamic alterations in mechanical properties still need to be disclosed due to the high heterogeneity of shale, particularly at the microscale. This paper aims to in-situ unravel the microscale changes in the dynamic mechanical properties of shale affected by fracturing fluids. A combination of nanoindentation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrum (EDS) techniques was employed. The nanoindentation results demonstrate a rapid initial decrease followed by a slower decline after 4 days in both Young's modulus and the hardness of shale exposed to fracturing fluids. Specifically, the average Young's modulus of shale ranges from 62.45 GPa to 56.275 GPa, 52.575 GPa, 40.15 GPa, and 39.5 GPa while the average hardness modulus varies from 3.305 GPa to 2.2125 GPa, 1.8175 GPa, 1.24 GPa and 1.1525 GPa with the treatment time of 0, 1, 2, 4, and 7 days, respectively. An exponential expression well describes the relationship between mechanical properties with the treatment time. XRD analysis shows carbonate and clay mineral content decrease, while quartz content increases. Moreover, in-situ SEM results highlight the emergence of many dissolution pores when shale is exposed to fracturing fluid. Further pH testing and EDS analysis indicates a corrosion effect, with hydrogen ions reacting with carbonate minerals in shale, leading to a significant reduction in calcite and dolomite. Consequently, the corrosion-induced dissolution pores weaken the stability of the shale matrix, leading to a reduction in mechanical properties. This study sheds light on the mechanism behind the dynamic mechanical properties of rock and provides valuable insights for optimizing the soaking time for fracturing fluids.

中文翻译：

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压裂液接触引起页岩微观力学变化的实验研究

了解暴露于压裂液的页岩力学性能的变化对于优化水力压裂参数至关重要。然而，由于页岩的高度非均质性，特别是在微观尺度上，机械性能的动态变化仍然需要披露。本文旨在原位揭示压裂液影响页岩动态力学性质的微观变化。采用纳米压痕、X 射线衍射 (XRD)、扫描电子显微镜 (SEM) 和能量色散谱 (EDS) 技术的组合。纳米压痕结果表明，暴露于压裂液的页岩的杨氏模量和硬度最初快速下降，然后在 4 天后缓慢下降。具体而言，随着处理时间的延长，页岩的平均杨氏模量变化范围为62.45 GPa～56.275 GPa、52.575 GPa、40.15 GPa和39.5 GPa，平均硬度模量变化范围为3.305 GPa～2.2125 GPa、1.8175 GPa、1.24 GPa和1.1525 GPa。分别为 0、1、2、4 和 7 天。指数表达式很好地描述了机械性能与处理时间之间的关系。 XRD分析表明碳酸盐和粘土矿物含量减少，而石英含量增加。此外，原位扫描电镜结果突出显示，当页岩暴露于压裂液时，会出现许多溶蚀孔隙。进一步的 pH 测试和 EDS 分析表明存在腐蚀效应，氢离子与页岩中的碳酸盐矿物发生反应，导致方解石和白云石显着减少。因此，腐蚀引起的溶蚀孔隙削弱了页岩基质的稳定性，导致力学性能下降。这项研究揭示了岩石动态力学特性背后的机制，并为优化压裂液浸泡时间提供了宝贵的见解。