Tracing the sources and evolution processes of shale gas by coupling stable (C, H) and noble gas isotopic compositions: Cases from Weiyuan and Changning in Sichuan Basin, China
Tracing the sources and evolution processes of shale gas by coupling stable (C, H) and noble gas isotopic compositions: Cases from Weiyuan and Changning in Sichuan Basin, China
复制标题
DOI：
10.1016/j.jngse.2020.103304
复制
发表时间：
2020-06-01
影响因子：
--
通讯作者：
Zhou, Zheng
中科院分区：
文献类型：
--
作者：
Cao, Chunhui;Zhang, Mingjie;Zhou, Zheng
龙马溪组页岩有机质来源和热演化历史仍存在争议。本研究分析了碳氢化合物（CH4、C2H6 和 C3H8）和 CO2 的分子和稳定碳同位素组成，以及甲烷、乙烷和稀有气体（He、Ne、Ar、Kr 和 Xe）的稳定氢同位素组成。 WY 和 CN 地区页岩气湿度极低，CH4 浓度范围为 93.41% 至 99.01%。非烃气体主要是N-2（0.22%-2.81%）和CO2（0.03%-1.35%）。未检测到H2S。 WY 和 CN 页岩气中不同的 Delta C-13(1) 和 Delta C-13(2) 值（WY：-37.3 至 -35.0 份和 -40.3 份至 -38.3 份，CN：-29.8 份至 -26.3 份和 -35.3 份至 -32.7 份）和各种碳同位素组成分布 碳氢化合物的模式（δ C-13（1）> δ C-13（2）δ C-13（2）> δ C-13（3））表明了复杂的演化过程。 WY 页岩气比 CN 页岩气含有更多的石油裂解气，表明 WY 页岩气更像来自 I-II 型有机质。在页岩气系统中，甲烷含量和δ C-13(1)比值随热演化程度的不同而变化，因此仅利用碳同位素数据无法确定页岩气的来源。 δ C-13(CO2) 值（-8.9 ppm 至 -0.8 ppm）和 N-2/(40) Ar 比率 (20.8-165.1) 的广泛范围表明气体的多个来源。峨眉山地幔柱为某些热成因气体提供了热源。稀有气体同位素组成（He-3/He-4：0.001Ra 至 0.019Ra）表明空气和地壳起源，地幔没有显着贡献。 Ar-40/Ar-36比值(1194.3～4604.5)与Ar同位素累积效应计算出的龙马溪地层年龄一致。页岩气湿度、碳同位素比和碳同位素组成分布模式可以包含指示页岩气甜点的信息。
The source and thermal evolution history of organic matter for the Longmaxi shale are still debated. This study analyzed the molecular and stable carbon isotopic compositions of hydrocarbons (CH4, C2H6, and C3H8) and CO2 as well as the stable hydrogen isotopic compositions of methane, ethane, and noble gases (He, Ne, Ar, Kr, and Xe). Shale gases in the WY and CN areas show an extremely-low-wetness with CH4 concentrations range from 93.41% to 99.01%. Non-hydrocarbon gases are mainly N-2 (0.22%-2.81%) and CO2 (0.03%-1.35%). H2S have not been detected. Different delta C-13(1) and delta C-13(2) values in WY and CN shale gases (WY: -37.3 parts per thousand to -35.0 parts per thousand and -40.3 parts per thousand to -38.3 parts per thousand, CN: -29.8 parts per thousand to -26.3 parts per thousand and -35.3 parts per thousand to -32.7 parts per thousand) and various carbon isotope-composition distribution patterns (delta C-13(1)>delta C-13(2)delta C-13(2)>delta C-13(3)) of hydrocarbons indicate a complex evolution process. WY shale gases include more oil-cracking gas than CN shale gases, suggesting WY shale gases more like come from Type I-II organic matter. In shale gas systems, methane content and delta C-13(1) ratios vary with the degree of thermal evolution, so the origin of shale gas cannot be determined using carbon isotope data alone. The wide range of delta C-13(CO2) values (-8.9 parts per thousand to -0.8 parts per thousand) and N-2/(40) Ar ratios (20.8-165.1) suggests multiple origins of the gases. Emeishan mantle plume provides the source of heat for some thermo-genic gas. Noble gas isotopic compositions (He-3/He-4: 0.001Ra to 0.019Ra) indicate air and crustal origins with no significant contribution from the mantle. Ar-40/Ar-36 ratios (1194.3-4604.5) are consistent with the age of Longmaxi strata calculated by accumulative effect of Ar isotope. The shale gas humidity, carbon isotope ratios, and the carbon isotope-composition distribution patterns may contain information indicating the shale gas sweet spot.