Abstract The pyrobitumen in conventional petroleum reservoirs is a thermally altered product of ancient oil pools, which may provide valuable source information using its molecular and isotopic signatures. Pyrobitumen formation is often associated with thermal alteration of asphaltene or polar-rich components rather than that of oil as a whole. Although asphaltenes are useful in source correlation of altered oils, the geochemical characteristics of asphaltene-derived pyrobitumen are poorly understood. In this study, artificial pyrobitumen formation through oil asphaltene cracking was performed at different thermal simulation (i.e., pyrolysis) temperatures. Systematic variations in the amounts and distributions of extractable and bound hydrocarbons, released by catalytic hydropyrolysis of the artificially produced pyrobitumen were studied. Pyrobitumen production yield was high at pyrolysis temperatures corresponding to post oil peak maturities, with a maximum yield of ∼70 wt% of asphaltene being reached in the early condensate–wet-gas stage. The molecular structure of pyrobitumen varied only slightly over the high maturity range (EasyRo 1.64–2.51%). Compared with the parent asphaltene, the pyrobitumen had a low biomarker (e.g., regular steranes and terpanes) content, and even the carbon isotopic values of the more stable bound n-alkanes were strongly altered. Thermal cracking of asphaltene alone, rather than whole oil, accelerates cross-linking of aromatic units, and cleavage or condensation of molecules bound in the pyrobitumen. These molecular changes suggest that care is needed when using the geochemical characteristics of bound hydrocarbons in natural pyrobitumen for source determinations. Nevertheless, the carbon isotopic ratios of bulk pyrobitumen hydropyrolysate were similar to those of bulk oil or pyrobitumen, even at very high maturities, suggesting these may be reliable indices for source tracing. A comparison of carbon isotopic compositions between pyrobitumen-bound and solvent-extractable n-alkanes could be useful in determining whether they have the same origin. Furthermore, the compositional and isotopic characteristics of bound hydrocarbons in pyrobitumen may provide information on the stage of maturity under geological conditions. The investigation of free and bound molecules may thus elucidate pyrobitumen genesis as related to its source, thermal maturity, and possible later hydrocarbon charging.

中文翻译：

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沥青质裂解快速形成的焦沥青的结合烃和结构：对油源关联的启示

摘要 常规油藏中的焦沥青是古代油藏的热变产物，利用其分子和同位素特征可以提供有价值的来源信息。焦沥青的形成通常与沥青质或富含极性的组分的热变有关，而不是与整个石油的热变有关。尽管沥青质可用于改变油源的相关性，但对沥青质衍生的焦沥青的地球化学特征知之甚少。在这项研究中，在不同的热模拟（即热解）温度下通过石油沥青质裂解形成人工焦沥青。研究了人工生产的焦沥青的催化加氢热解所释放的可提取和结合烃的数量和分布的系统变化。在对应于油后峰值成熟度的热解温度下，焦沥青的产量很高，在早期凝析油 - 湿气阶段达到了约 70 wt% 的最大沥青质产量。焦沥青的分子结构在高成熟度范围（EasyRo 1.64–2.51%）内仅略有变化。与母体沥青质相比，焦沥青的生物标志物（例如，常规甾烷和萜烷）含量较低，甚至更稳定的结合正构烷烃的碳同位素值也发生了强烈变化。单独热裂解沥青质而不是整个油会加速芳香族单元的交联，以及结合在焦沥青中的分子的裂解或缩合。这些分子变化表明，在使用天然焦沥青中结合碳氢化合物的地球化学特征进行来源测定时需要小心。尽管如此，散装焦沥青水解物的碳同位素比与散装油或焦沥青的碳同位素比相似，即使在非常高的成熟度下，这表明这些可能是溯源的可靠指标。焦沥青结合的正构烷烃和溶剂可萃取的正构烷烃之间的碳同位素组成的比较有助于确定它们是否具有相同的来源。此外，焦沥青中结合烃的成分和同位素特征可以提供有关地质条件下成熟阶段的信息。因此，对游离和结合分子的研究可以阐明焦沥青的成因与其来源、热成熟度、