在线裂解色谱—同位素比值质谱测定天然气丙烷位碳同位素及其初步应用

Measurements of position-specific carbon isotopic compositions in propane by on-line Gas Chromatography-Pyrolysis-Gas Chromatography-Isotope Ratio Mass Spectrometer (GC-Py-GC-IRMS) and its preliminary application

马媛媛 陶成 把立强 王杰 李吉鹏 李璐赟 孙永革

MA Yuanyuan TAO Cheng BA Liqiang WANG Jie LI Jipeng LI Luyun SUN Yongge

中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126 中国石化 油气成藏重点实验室, 江苏 无锡 214126 浙江大学 地球科学学院 有机地球化学研究组, 杭州 31002

Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China SINOPEC Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi, Jiangsu 214126, China Organic Geochemistry Unit, School of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027, China

遵循富集、色谱分离、瞬时裂解、同位素比值测试原则，搭建了气相色谱—裂解—气相色谱同位素比值质谱(GC-Py-GC-IRMS)在线位碳同位素测试系统用以测定特定化合物位碳同位素组成。由于丙烷瞬时裂解严格受控于动力学过程，因此，以丙烷为例，考察不同温度下丙烷裂解转化率以及裂解产物碳同位素组成，获得该测试系统丙烷的最佳裂解温度为780~820 ℃，并根据丙烷裂解动力学分馏模型，计算获得丙烷位碳同位素组成。对鄂尔多斯盆地大牛地气田已知上古生界煤系成因两件天然气样品丙烷位碳同位素进行了测定，结果表明，奥陶系马家沟组五段气藏和石炭—二叠系气藏天然气丙烷中心碳相同的碳同位素组成可能指示二者具有相同的气源，而石炭—二叠系气藏天然气丙烷端元碳同位素显著富集13C，则指示了其高演化阶段成因特征。研究成果初步展示了丙烷位碳同位素组成在天然气成因研究中具有广阔应用前景。

In this study, an on-line Gas Chromatography-Pyrolysis-Gas Chromatography-Isotope Ratio Mass Spectrometer (GC-Py-GC-IRMS) was established to conduct position-specific isotope analysis (PSIA) by enrichment of compound interested, chromatographic separation, instantaneous pyrolysis and isotope ratio measurement. Propane, as its instantaneous pyrolysis can be kinetically controlled, was selected for tests. The molar conversion (mol%) of propane during pyrolysis and the carbon isotopic compositions of pyrolysis products upon temperature sequence show that the optimal pyrolysis temperature of propane is 780-820 ℃ for its position-specific carbon isotope analysis. Integrated with carbon isotopic fractionation during the propane pyrolysis, the carbon isotopes of central and terminal carbon were successfully calculated. Two natural gas samples from the Daniudi Gas Field, Ordos Basin were collected for central and terminal carbon isotope measurements in propane. Similar δ13C values of central carbon of propane in natural gas from the Ordovician and Carboniferous-Permian reservoirs could be indicative of the same source strata. While 13C-enrichment in the terminal C-atom of propane in natural gas from the Carboniferous-Permian reservoirs probably indicates that natural gas accumulated in the Carboniferous-Permian reservoir maybe have experienced a higher thermal maturation compared to that from the Ordovician reservoirs. The results suggest that the PSIA in propane can be a potentially powerful tool to probe the mechanisms on natural gas generation.

国家自然科学基金 42030803;中国石化科技部项目 P21035-1

https://doi.org/10.11781/sysydz202202350