珠江口盆地东部油气系统地球化学-Ⅰ:油组划分、油源对比及混源油确定  

Geochemistry of Petroleum Systems in the Eastern Pearl River Mouth Basin-I:Oil Family Classification, Oil-source Correlation and Mixed Oil Analysis

作　　者：张水昌[1] 龚再升[2] 梁狄刚[1] 吴克强 汪建蓉 宋孚庆[1] 王培荣[1] 王汇彤[1] 何忠华[1] 

机构地区：[1]中国石油勘探开发研究院 [2]中国海洋石油总公司,北京100027 [3]中国海洋石油研究中心勘探研究院,河北高碑店074010 [4]中国海洋石油东部公司研究院,广州510240

出　　处：《沉积学报》2004年第B06期15-26,共12页Acta Sedimentologica Sinica

摘　　要：对珠江口盆地东部原油和烃源岩抽提物进行了详细的生物标志化合物检测,结果发现存在两类不同特征的原油,第一类原油含有丰富的C304-甲基甾烷,而C19三环萜烷、双杜松烷(主要是T构型)等代表陆生高等植物生源的分子化合物浓度低,与典型湖相沉积的文昌组烃源岩有良好的可比性;另一类原油具有高丰度的双杜松烷和C19三环萜烷以及较高的Pr/Ph值等,代表着偏氧化环境下以高等植物生源为主的恩平组湖沼相烃源岩的贡献,但这类原油中同时也不同程度地含有只是在文昌组岩石中才有的C304-甲基甾烷,因而认为这类油是两套烃源岩的混源产物,恩平组原油的混合比例最高可达80%以上,主要分布在惠州凹陷及其南边的西惠地凸起上。原油配比实验表明,即使在文昌组生成的原油中加入50%-80%的恩平组原油,混合油仍表现出文昌组生源的特征。因此,4-甲基甾烷的存在不能作为判识珠江口盆地东部油源主要是文昌组的唯一证据。文昌组烃源岩对珠-坳陷商业性油藏的贡献是普遍的,但恩平组烃源岩对惠州凹陷周边凸起上的油田/油藏的显著贡献不容忽视。正是由于恩平组生成的原油的再次注入,使得早期发生生物降解了的油藏再次充满,使油质变轻。Detailed analyses of crude oils and source rock extracts indicate the presence of two, effective petroleum source rocks in the eastern Pearl River Mouth Basin of the South China Sea region. Oils derived from the lacustrine source rocks in the Eocene Wenchang Formation are characterized by abundant C30 4 methyl steranes with relatively little C19 tricyclic terpane and bicadinanes. In contrast, oils from an Eocene-Oligocene Enping Formation source typically contain significant amounts of C19 tricyclic terpane and bicadinanes, with relatively little 4-methylsteranes and high pristane/phytane ratios. However, the chemical compositions of a large number of oils do not conform to those of the unknown source rocks. consistent with the mixing of the two sources. Mixed oils occur mainly in the Huizhou Sag and along its south margin, and the highest proportion of the Enping Formation source in the mixed oils is estimated to be around 80%. Laboratory mixing experiments using selected end-member oils indicate that, even with 50 to 80% contribution from the Enping Formation source, the mixture still display sterane biomarker signatures diagnostic of the Wenchang Formation source. Therefore, the presence of abundant 4-methyl steranes is a necessary but not sufficient indicator for the Wenchang Formation source in the eastern Pearl River Mouth Basin. Although our results support the Wenchang Formation as a major source to the known oil discoveries in the study area, the contribution of the Enping Formation source to traps in the Huizhou Sag and surrounding area cannot be ignored. There is clear evidence for the recharge of Enping Formation derived oils into the early-biodegraded oil reservoirs to form light oil accumulations.

关 键 词：地球化学 油组划分 烃源岩 生物标志化合物 湖相沉积 

分 类 号：P593[天文地球—地球化学]