As the three-dimensional (3D) molecular structure of kerogen plays important roles in further understanding of shale gas storage and transport, accurate characterization methods for 3D kerogen structures are attracting increasing attention. Spatial alignment is important information for 3D kerogen modeling, but was usually ignored in previous studies. In this work, seven kerogen samples with different maturities were isolated from organic-rich shale using a chemical method and high-resolution transmission electron microscopy (HRTEM) was employed to quantitatively characterize the spatial alignment of these seven kerogen samples. Raman spectroscopy was used to investigate the overall structural disorder of the kerogen molecules and Fourier transform infrared (FT-IR) was conducted to study the chemical structure of these kerogen samples. The results show that immature, mature, and overmature kerogen samples all show an obvious alignment on the scale of 20 nm × 20 nm. In the immature kerogen sample Yl-1 with equivalent vitrinite reflectance (VR_eqv) = 0.4%, 60% of total aromatic fringes align in the major direction (with a 60° range), while 87% of the total aromatic fringes align in the major direction for the overmature kerogen sample Lmx-3 (VR_eqv = 3.1%). However, unlike local alignment in the scale of 20 nm × 20 nm, the aromatic fringes in different regions may have different directions in larger scale. Meanwhile, based on FT-IR data, aliphatic carbons and oxygen containing functional groups contribute to a large proportion in immature, mature, and overmature kerogen samples. Thus, immature, mature and overmature kerogen samples all show overall disorder according to Raman data. In addition, the size of aromatic rings is also quantitatively characterized based on HRTEM images. In immature kerogen samples, the proportion of aromatic rings smaller than 3 × 3 is larger than 70%. In mature and overmature kerogen samples, 3 × 3 sized aromatic rings always occupy the largest proportion. This study provides the quantitative information on spatial alignment and the size of aromatic rings for kerogen samples, which contribute to an improved understanding of the 3D structure of kerogen.

中文翻译：

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高分辨率透射电镜，拉曼光谱和傅里叶变换红外光谱法评价页岩中干酪根的空间排列

由于干酪根的三维（3D）分子结构在进一步理解页岩气的储藏和运输中起着重要作用，因此3D干酪根结构的准确表征方法正引起越来越多的关注。空间对齐是3D干酪根建模的重要信息，但在以前的研究中通常忽略不计。在这项工作中，使用化学方法从富含有机物的页岩中分离出七个成熟度不同的干酪根样品，并采用高分辨率透射电子显微镜（HRTEM）定量表征了这七个干酪根样品的空间排列。拉曼光谱用于研究干酪根分子的整体结构紊乱，并进行傅立叶变换红外（FT-IR）研究这些干酪根样品的化学结构。结果显示，未成熟，成熟和过成熟的干酪根样品均在20 nm×20 nm的范围内显示出明显的对齐方式。在未成熟的干酪根样品Y1-1中具有等效的镜质体反射率（VR_eqv）= 0.4％，过早的干酪根样品Lmx-3（VR _eqv= 3.1％）。但是，与20 nm×20 nm范围内的局部排列不同，不同区域的芳香族条纹在较大范围内可能具有不同的方向。同时，根据FT-IR数据，脂族碳和含氧官能团在未成熟，成熟和过成熟的干酪根样品中占很大比例。因此，根据拉曼数据，未成熟，成熟和过成熟的干酪根样品均显示出总体紊乱。另外，芳族环的大小也基于HRTEM图像被定量表征。在未成熟的干酪根样品中，小于3×3的芳环比例大于70％。在成熟和过早的干酪根样品中，3×3大小的芳环始终占据最大比例。