珠江口盆地惠西南地区凝析油轻烃地球化学特征

惠西南地区是珠江口盆地珠一坳陷重要的原油富集区, 但近年来在新近系珠江组上段和古近系恩平组、文昌组以及基岩潜山储层中陆续发现了凝析油气。利用全油气相色谱和饱和烃色谱-质谱分析技术对凝析油样开展了轻烃和生物标志化合物地球化学特征分析, 探讨了惠西南地区凝析油的成因。研究表明: 轻烃组分特征、C₇异构烷烃、环烷烃及正构烷烃和生物标志化合物特征均指示H6-1构造凝析油来源于半深湖-深湖相文昌组烃源岩, 为腐泥型烃源岩在相对高成熟阶段(R_o处于1.2%~1.3%)生成的凝析油; H1-1构造凝析油来源于浅湖沼泽相恩平组烃源岩, 为偏腐殖型烃源岩在相对低成熟阶段(R_o处于0.9%~1.1%)生成的富低碳数烷烃油气; 揭示了惠西南凝析油的形成受到烃源母质类型和热演化阶段的双重控制。研究结果为富油生烃凹陷凝析油气勘探潜力评价分析提供了地球化学依据和支撑。 

Geochemical characteristics of light hydrocarbons in condensate oil from the southwestern Huizhou of the Pearl River Mouth Basin

The southwestern Huizhou is an important crude oil enrichment area in the Zhu Ⅰ Depression of the Pearl River Mouth Basin. However, condensate oil and gas have been discovered in the upper memberof Neogene Zhujiang Formation, Paleogene Enping and Wenchang formations, and basement buried hill reservoirs in recent years. In this study, the origin of condensate oil was revealed based on the integration of light hydrocarbons and biomarkers characteristics, which were obtained from GC of whole-oil and GC-MS of saturated fractions.The results, including light hydrocarbon composition, C₇ is o-alkanes, naphthene, n-alkanes and other biomarkers indicate that the condensate oil in the H6-1 structure came from the semi-deep to deep lacustrine source rock in Wenchang Formation, which was generated by sapropelic kerogen with relatively high maturity (1.2%-1.3% R_o). In contrast, the condensate oil in the H1-1 structure originated from the shallow lake to peat facies source rock in Enping Formation, the oil was rich in alkanes with low-carbon number which was generated by humic kerogen with relatively low maturity (0.9%-1.1% R_o).The results suggest that the formation of condensate oil in the southwestern Huizhou is both controlled by organic matter type and thermal evolution stage of source rock. This study provides a geochemical basis and support for the evaluation and analysis of condensate oil and gas exploration potential in hydrocarbon-rich depressions.