安页1井志留系龙马溪组页岩有机质拉曼光谱特征及其地质意义

我国下古生界海相页岩有机质热演化程度普遍高、陆源植物镜质体缺乏,显微组分难以区分,现有镜质体反射率、岩石热解、Tm/Ts等生物标志化合物指标的测试方法难以有效评价泥页岩有机质成熟度。本文以贵州正安地区安页1井志留系龙马溪组页岩为研究对象,利用场发射扫描电镜观察和激光拉曼光谱检测相结合,不依赖于有机质显微组分类型,直接获取高演化页岩中不同赋存状态有机质的拉曼谱图,利用拉曼谱图衍生参数评价高演化页岩的有机质成熟度。结果表明:安页1井志留系龙马溪组页岩发育着生物结构型、脉状或团块状、自形边界填隙状、他形边界填隙状4种类型有机质,其中自形边界填隙状有机质孔径大于80nm,他形边界填隙状有机质孔径小于60nm,这两种填隙状占比在90%以上,是页岩储层的主体储集空间;4种形态的有机质热演化程度不一致。激光拉曼面扫描取谱方式获得大量数据计算的拉曼成熟度主体介于2. 8%～3. 0%,各类型有机质的拉曼成熟度数量占总数量的比例与场发射扫描电镜观测的半定量统计结果一致。该方法为刻画我国高-过成熟度页岩有机质成熟度提供了一种行之有效的手段。

Raman Spectrum Characteristics of Organic Matter in Silurian Longmaxi Formation Shale of Well Anye-1 and Its Geological Significance

BACKGROUND: The higher thermal maturity of organic matter and the shortage of terrestrial plants are the main characteristics of Lower Paleozoic marine shale in China, which results in the difficulty of distinguishing macerals. Nowadays the existing methods of vitrinite reflectance, rock eval, Tm/Ts and other biomarker indices cannot be effectively used to evaluate the maturity of organic matter in shale.
OBJECTIVES: To evaluate the maturity of organic matter in highly evolved shale.
METHODS: The shale of the Silurian Longmaxi Formation of Well Anye-1 in Zheng''an area of Guizhou Province is used in the experiments. Field Emission Scanning Electron Microscopy and Laser Raman Spectroscopy are used to obtain the Raman Spectra of organic matter in different occurrences of highly evolved shale, independent of the type of organic macerals.
RESULTS: It can be found that there are four types of organic matter in the Silurian Longmaxi Formation of Well Anye-1, i.e. bio-structural type, vein-like or clump-like type, euhedral and anhedral boundary filling gap shape. The euhdedral boundary filling gap shape has an organic aperture larger than 80nm, whereas the anhedral boundary filling gap shape has an organic aperture less than 60nm. These two types of organic matter are the main reservoir space of rock reservoirs, which account for more than 90%. Four types of organic matter have different thermal evolution degrees. Moreover, the Raman maturity ranges from 2.8% to 3.0%, which is calculated from the laser Raman surface scanning data. The proportion of Raman maturity of various organic matters to the total amount is consistent with the semi-quantitative statistical results observed by Field Emission Scanning Electron Microscopy.
CONCLUSIONS: The methods used in the experiments are effective in measuring the maturity of organic matter in highly evolved marine shale in China.