Abstract A single-step method allowing the measurement of 13C intramolecular distribution of butane isomers (n- and i-butane) from natural gas samples was developed. The method builds up on the one that has been developed for propane, using on-line pyrolysis followed by isotope analysis of the pyrolytic fragments. The isotopic filiation between n-butane and its pyrolytic fragments was elucidated using samples spiked with 13C on terminal positions. The isotopic filiation for i-butane could not be shown experimentally due to the lack of commercially available enriched i-butane. We thus used a recent model named Reaction Mechanism Generator (RMG) to assess the origin of the fragments arising from i-butane pyrolysis. Butanes from natural gas samples from the Carnarvon Basin (Australia) and the Arkoma Basin (USA) were analyzed. The results are consistent with a model for thermogenic natural gas generation and suggest that combined intramolecular isotope composition of propane and n-butane can be related to the gas maturity. In addition, the method allows the detection and shed light on the mechanism of n-butane and i-butane biodegradation in natural gas reservoirs.

中文翻译：

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天然气中丁烷的分子内 13C 同位素分布

摘要 开发了一种单步法，可以测量天然气样品中丁烷异构体（正丁烷和异丁烷）的 13C 分子内分布。该方法建立在为丙烷开发的方法的基础上，使用在线热解，然后对热解碎片进行同位素分析。使用在末端位置加标 13C 的样品阐明了正丁烷与其热解碎片之间的同位素关系。由于缺乏市售的富集异丁烷，异丁烷的同位素分枝无法通过实验显示。因此，我们使用了一种名为反应机制生成器 (RMG) 的最新模型来评估异丁烷热解产生的碎片的来源。分析了来自 Carnarvon 盆地（澳大利亚）和 Arkoma 盆地（美国）的天然气样品中的丁烷。结果与热成因天然气生成模型一致，表明丙烷和正丁烷的分子内同位素组成与天然气成熟度有关。此外，该方法允许检测和阐明天然气藏中正丁烷和异丁烷生物降解的机制。