Influence of non-thermal maturity factors on laser Raman spectroscopy of highly to overmature shale: a case study of Lower Paleozoic marine shale in southern Sichuan Basin
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摘要: 激光拉曼光谱技术因其样品制备过程简单、测试便捷及具备无损分析等优势，在古老海相页岩热成熟度评价领域的应用日益广泛。目前，国内外研究主要聚焦于激光拉曼相关参数对热成熟度变化的响应，而对于非热成熟度因素(如谱图处理、样品预处理、激光波长设置等)对实验精度影响的研究相对匮乏且认识不一。采用激光拉曼光谱技术对四川盆地上奥陶统五峰组—下志留统龙马溪组及下寒武统筇竹寺组高—过成熟黑色页岩进行系统对比分析，重点探讨非热成熟度因素对激光拉曼光谱峰间距(RBS)、半峰宽(FWHM)、峰强比(ID/IG)等参数的影响，主要获得如下认识：(1)在图谱处理方法方面，双峰拟合较五峰拟合的不确定性更小、处理效率更高，更契合高—过成熟页岩热成熟度测试的需求，适用于筇竹寺组页岩拉曼谱图处理；(2)在参数选择方面，位置参数(WD、WG、RBS)经分峰拟合后，热成熟度差异小于2%，稳定性较高，而峰形参数(ID/IG、FWHM-D、FWHM-G)中的ID/IG受分峰拟合影响较小且样品间区分度高，建议在热成熟度相关性研究中优先选用位置参数RBS与峰形参数ID/IG；(3)在样品预处理方面，抛光处理对五峰组—龙马溪组高—过成熟黑色页岩拉曼参数的影响整体小于3%，但为确保能够准确定位黑色页岩中的分散有机质，建议在实验前对样品进行抛光处理。Abstract: Laser Raman spectroscopy has become increasingly prevalent in assessing the thermal maturity of ancient marine shale due to its advantages of simple sample preparation, easy operation, and non-destructive analysis. Current studies primarily focus on the response of Raman spectral parameters to thermal maturity variations, while research on the influence of non-thermal maturity factors, such as spectrum processing methods, sample pretreatment, and laser wavelength settings, on experimental accuracy remains relatively scarce and inconsistent. Using laser Raman spectroscopy, this study conducted a systematic comparative analysis of highly to overmature black shale samples from the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation and Lower Cambrian Qiongzhusi Formation in the Sichuan Basin, with a particular focus on the impact of non-thermal maturity factors on parameters such as Raman band separation (RBS), full width at half maximum (FWHM), and the intensity ratio of D peak to G peak (ID/IG). The findings are as follows: (1) Spectrum processing methods: Two-peak fitting demonstrated lower uncertainty and higher efficiency than five-peak fitting, making it more suitable for thermal maturity assessment of highly to overmature shale, especially for the processing of Raman spectra of shale in Qiongzhusi Formation. (2) Parameter selection: Positional parameters (WD, WG, and RBS) showed thermal maturity differences of less than 2% after peak fitting, indicating high stability. Conversely, among the peak shape parameters (ID/IG, FWHM-D, FWHM-G), ID/IG was less affected by peak fitting and demonstrated better sample discrimination. Therefore, RBS and ID/IG are recommended as priority parameters in thermal maturity correlation studies. (3) Sample pretreatment: Polishing treatment has an overall impact of less than 3% on the Raman parameters of highly to overmature black shale from the Wufeng Formation and Longmaxi Formation. However, to accurately locate the dispersed organic matter within the black shale, polishing prior to Raman analysis is recommended.
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Key words:
- organic petrography /
- organic matter /
- Raman spectral parameters /
- peak fitting /
- Sichuan Basin
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图 2 川南上寒武统五峰组—下奥陶统龙马溪组典型页岩样品激光拉曼光谱平滑处理与基线校准对比
Figure 2. Comparison of smoothed laser Raman spectra and baseline calibration of typical shale samples from Upper Cambrian Wufeng Formation to Lower Ordovician Longmaxi Formation in southern Sichuan Basin
图 3 川南上奥陶统五峰组—下志留统龙马溪组与下寒武统筇竹寺组典型样品不同分峰方式拟合效果
Figure 3. Fitting results of different peak fitting methods for typical samples from Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation and Lower Cambrian Qiongzhusi Formation in southern Sichuan Basin
图 4 川南下古生界样品双峰拟合与五峰拟合对比
Figure 4. Comparison between double-peak and five-peak fitting of samples in Lower Paleozoic of southern Sichuan Basin
图 5 川南下古生界筇竹寺组典型样品抛光与未抛光镜下照片对比
Figure 5. Microscopic images comparing polished and unpolished typical samples from Lower Paleozoic Qiongzhusi Formation in southern Sichuan Basin
表 1 川南下古生界黑色页岩样品信息
Table 1. Information of black shale samples from Lower Paleozoic in southern Sichuan Basin
井号 样品编号 深度/m 层位 ω(TOC)/% 样品数量 Z213 1~9 4 108.70~4 092.78 五峰组—龙马溪组 2.11~4.88 9 Z205 18~25 4 103.73~4 099.05 龙马溪组 8 W120 47~55 2 822.13~2 829.52 筇竹寺组 9 N206 76~82 1 889.73~1 330.11 筇竹寺组 0.83~3.58 7 W201 83~88 2 629.15~2 819.40 筇竹寺组 0.37~5.69 6 H201 89~100 4 052.80-4 085.60 龙马溪组 13 
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表 2 川南上奥陶统五峰组—下志留统龙马溪组典型页岩样品平滑处理中不同窗口对各类参数的影响
Table 2. Influence of different smoothing window sizes on each parameter of typical shale samples from Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation in southern Sichuan Basin
窗口大小 RBS/cm-1 WG/cm-1 WD/cm-1 FWHM-G/cm-1 FWHM-D/cm-1 ID/IG 原始数据 270.40 1 603.16 1 332.76 32.15 60.73 0.75 5 270.38 1 603.16 1 332.78 32.16 60.99 0.75 7 270.42 1 603.18 1 332.75 31.92 60.23 0.74 9 270.61 1 603.24 1 332.63 31.51 55.90 0.66 11 270.62 1 603.24 1 332.61 31.43 55.82 0.66 13 270.58 1 603.24 1 332.65 31.56 56.21 0.67 15 270.58 1 603.23 1 332.65 31.61 56.25 0.67 17 270.88 1 603.24 1 332.36 30.19 54.61 0.68 19 270.74 1 603.23 1 332.49 30.81 55.55 0.68 21 270.55 1 603.22 1 332.66 31.79 56.62 0.67
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表 3 川南上奥陶统五峰组—下志留统龙马溪组典型页岩样品不同基线校准拉曼参数对比
Table 3. Comparison of Raman parameters with different baseline calibrations for typical shale samples from Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation in southern Sichuan Basin
基线类型 WD/cm-1 WG/cm-1 RBS ID/IG FWHM-G/cm-1 FWHM-G/cm-1 未校准 1 324.85 1 597.68 272.83 1.25 - - 线性 1 331.55 1 599.03 267.48 0.84 116.09 39.74 最佳拟合 1 329.62 1 599.22 269.60 0.80 117.94 41.16 三次多项式 1 324.92 1 597.24 272.31 0.91 113.16 75.70 对数 1 331.00 1 598.59 267.59 0.85 118.17 40.75
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表 4 川南上古生界样品双峰拟合与五峰拟合差值百分比
Table 4. Percentage difference between double-peak and five-peak fitting of samples in Upper Paleozoic of southern Sichuan Basin
% 井号 WD WG RBS ID/IG FWHM-D FWHM-G W120 0.71 0.24 -1.92 17.74 -36.32 -18.38 N206 0.14 0.25 0.78 10.09 -6.95 -13.47 W201 0.41 0.16 -1.14 10.29 -24.92 -12.04 Z213 0.43 0.17 -1.11 7.46 -32.31 -13.69 Z205 0.48 0.15 -1.48 4.55 -31.95 -15.03 H201 0.17 0.16 0.39 11.54 -20.28 -10.21
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表 5 川南上奥陶统五峰组—下志留统龙马溪组抛光与未抛光样品拉曼参数对比
Table 5. Comparison of Raman parameters between polished and unpolished samples from Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation in southern Sichuan Basin
抛光情况 样品编号 WD/cm-1 WG/cm-1 RBS/cm-1 ID/IG FWHM-D/cm-1 FWHM-G/cm-1 抛光 Z205-22-1 1 327.93 1 598.63 270.70 0.68 162.42 44.45 Z205-22-2 1 328.54 1 600.61 272.07 0.64 162.78 43.21 Z205-22-3 1 328.61 1 597.58 268.97 0.70 172.26 46.67 Z205-22-5 1 329.44 1 599.04 269.60 0.66 173.82 45.88 未抛光 Z205-22-1 1 325.71 1 595.88 270.17 0.66 172.58 45.85 Z205-22-2 1 325.41 1 594.61 269.20 0.70 175.36 49.31 Z205-22-3 1 324.68 1 594.85 270.17 0.69 159.92 44.41 Z205-22-5 1 325.00 1 595.13 270.13 0.69 164.66 46.12
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