天然气氢同位素分析及应用

气相色谱—高温裂解—质谱在线分析方法可用于测定天然气氢同位素组成.通过实验优选了质谱仪离子源参数和色谱工作条件,探讨了H₃⁺因子、色谱柱流速、涂碳等因素对分析结果的影响.参考标准气连续多次测定结果表明天然气氢同位素在线分析具有良好的重现性.应用该方法分析了四川盆地部分天然气样品.依据天然气单体氢同位素组成的差异,结合已知地质文献资料进一步验证了川西侏罗系浅层气藏为高成熟或过成熟陆相煤成气天然气藏,川东地区气藏甲烷氢同位素大于-135‰,明显重于川西地区,反映典型的海相成因天然气特征.

ANALYSIS AND APPLICATION OF HYDROGEN ISOTOPIC COMPOSITION OF THE NATURAL GAS

The gas chromatography thermo-conversion mass spectrometry (GCTC-IRMS) can be used to detect the hydrogen isotopic composition of the natural gas.An experiment has been conducted first to optimize the MS ion source parameters and the GC conditions.The effects of the H₃+ factor,the GC flow rate and the carbon stick-coated conditioning of the thermo-conversion reactor on the analysis results have been discussed.The results prove that this isotopic measurement method has high reproductivity when compared with the numerous analysis results of the certified reference natural gas.The ana-lysis results of the hydrogen isotopic composition of some gas samples from the Sichuan Basin are pre-sented.Combined with the existing regional geological data,the hydrogen isotopic differences between the individual hydrocarbon gases prove that the gas in the shallow Jurassic reservoir in the western Sichuan Basin is coal-formed hydrocarbons from the high to over mature continental source rocks.The results also show that the hydrogen isotopic value of the methane from the eastern Sichuan Basin is higher than-135‰,heavier obviously than that from the western Sichuan Basin,indicating that the gas from the eastern Sichuan Basin is typically characterized by the marine origin.