Quantitative characterization of the geo-mechanical properties of shale and organic matter (OM) holds paramount significance in the assessment of shale gas reserves and the design of hydraulic fracturing. However, the mechanical evolution processes during shale hydrocarbon generation and its influencing factors have received limited attention. This study examines the changes in shale mechanical properties during pyrolysis at high temperatures (415–600 °C) and high pressure (50–125 MPa) for mature to over-mature stages. The nanoindentation and in-situ AFM-QNM analysis are utilized to characterize the changes in mechanical properties during evolution. Subsequently, gas adsorption, Fourier Transform infrared spectroscopy (FTIR), and laser Raman spectroscopy (Raman) are used to investigate the factors influencing the mechanical properties of shale and the associated OM, and establish a model for the evolution of the mechanical properties. The results demonstrate that with increasing maturity, the overall Young's modulus of the bulk shale gradually increases from 42.8 GPa to 58.4 GPa for the temperature increment from 415 °C to 600 °C. During the thermal maturation process, the mesopore structure and quartz content of the shale significantly influence its mechanical properties. Young's modulus of OM shows an S-shaped trend, with variations in the micromechanical properties of OM corresponding to stages of hydrocarbon generation. In particular, two peaks of Young's modulus increase are observed during the mature and over-mature stages. In the mature stage, the aromatization of the kerogen leads to substantial detachment of aliphatic side chains and oxygenated functional groups, resulting in a higher degree of aromatization. This reduces the kerogen spacing and consequently increases the Young's modulus. In the over-matured stage, the process of aromatics condensation leads to the orientation and arrangement of aromatic rings, reducing the number of key site vacancies and crystal defects, thereby forming large aromatic clusters and significantly increasing the graphite-like structure. This study will facilitate the analysis of shale matrix deformation mechanisms at the microscale, providing a fundamental theoretical and scientific basis for shale fracturing design, exploration, and development.

中文翻译：

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页岩在热解过程中的机械性能：原子力显微镜和纳米压痕研究


页岩和有机质 （OM） 地质力学性质的定量表征在页岩气储量评估和水力压裂设计中具有至关重要的意义。然而，页岩烃生成过程中的机械演化过程及其影响因素受到的关注有限。本研究研究了在高温 （415-600 °C） 和高压 （50-125 MPa） 下热解过程中页岩机械性能的变化，从成熟到过成熟阶段。纳米压痕和原位 AFM-QNM 分析用于表征进化过程中机械性能的变化。随后，使用气体吸附、傅里叶变换红外光谱 （FTIR） 和激光拉曼光谱 （Raman） 研究影响页岩和相关 OM 力学性能的因素，并建立力学性能演变模型。结果表明，随着成熟度的增加，随着温度从 415 °C 增加到 600 °C，块状页岩的整体杨氏模量逐渐从 42.8 GPa 增加到 58.4 GPa。 在热成熟过程中，页岩的中孔结构和石英含量显著影响其力学性能。OM 的杨氏模量呈 S 形趋势，OM 的微观机械性能变化对应于碳氢化合物生成的阶段。特别是，在成熟和过成熟阶段观察到杨氏模量增加的两个峰值。在成熟阶段，干酪根的芳构化导致脂肪族侧链和含氧官能团的大量分离，从而导致更高程度的芳构化。 这减小了干酪根间距，从而增加了杨氏模量。在过熟阶段，芳烃缩合过程导致芳烃环的取向和排列，减少了关键位点空位和晶体缺陷的数量，从而形成大的芳烃簇，显著增加了石墨状结构。本研究将有助于在微观尺度上分析页岩基质变形机制，为页岩压裂设计、勘探和开发提供基础理论和科学基础。