珠江口盆地惠州凹陷及其邻区原油分类和分布特征

20多年来,在珠江口盆地惠州凹陷及邻区发现了一批油气田和含油气构造。原油的生物标志化合物分析结果表明,惠州凹陷及邻区原油可分为3类:Ⅰ类原油主要来源于文昌组中深湖相烃源岩,具有高的C₃₀4-甲基甾烷和低的双杜松烷含量;Ⅱ类原油主要来源于恩平组烃源岩,具有高的双杜松烷和低的C₃₀4-甲基甾烷含量;Ⅲ类原油为文昌组中深湖相烃源岩和恩平组烃源岩混合来源,C₃₀4-甲基甾烷和双杜松烷含量均较高。从平面分布看,Ⅰ类原油主要分布于远离凹陷的凸起区;Ⅱ类原油主要分布于惠州凹陷内恩平组烃源岩发育的地区;Ⅲ类原油分布于惠州凹陷内文昌组中深湖相和恩平组烃源岩共同发育的地区。从纵向分布看,Ⅰ类原油主要分布于浅层的韩江组和珠江组;Ⅱ类原油主要分布于中深层的恩平组和珠海组;Ⅲ类原油在珠海组、珠江组和韩江组均有分布。

Classification and distribution of oil in Huizhou Depression of Pearl River Mouth Basin

Many oilfields and oil-bearing traps have been found in Huizhou Depression and its neighboring area in recent years. Oils in Huizhou Depression and its neighboring area can be classified to three types according to their biomarker characteristics. Type-I oil mainly originated from the middle-deep lacustrine source rock in Wenchang Formation and had high content of C_(30)4-methyl steranes and low content of bicadinanes. Type-Ⅱ oil was mainly derived from source rock of Enping Formation and had high content of bica-dinanes and low content of C_(30)4-methyl steranes. Type-Ⅲ oil came from the middle-deep lacustrine source rocks in Wenchang and Enping formations and had relatively high content of C_(30)4-methyl steranes and bicadinanes. Regionally, type- I oil mainly distributed at the uplift area. Type-Ⅱ oil mainly distributed inside the sags that have good source rock of Enping Formation and poor source rock of Wenchang Formation. Type-Ⅲ oil mainly distributed inside the sags that have good middle-deep lacustrine source rocks of Wenchang and Enping formations. Vertically, type- I oil mainly distributed at shallow layers of Hangjiang and Zhujiang formations. Type-Ⅱ oil mainly distributed at deep Enping and Zhuhai formations, and type-Ⅲ oil commonly distributed at Hangjiang, Zhujiang and Zhuhai formations.