珠一坳陷惠州西凹混源油研究

Research on Mixed Oil in Western Huizhou Sag of Zhu I Depression

详细的原油和烃源岩抽提物分析表明,珠江口盆地东部地区存在两套有效的烃源岩。源自始新统湖相烃源岩的典型原油具有丰富的C304-甲基甾烷和相对较低的双杜松烷化合物(T)特征。与之相反,源自渐新统恩平组的典型原油则具有高含量的双杜松烷化合物(T)、高Pr/Ph比值以及相对低含量的C304-甲基甾烷。然而,绝大多数原油的化学组成特征与那些未知烃源岩不相匹配,而与这两套烃源岩的混合特征相一致。其油源对比结果表明,西江24-3、西江24-1原油主要来自西江24洼文昌组和恩平组烃源岩,而西江30-2原油主要来自西江30洼文昌组烃源岩。原油的化学组成受洼陷内烃源岩组合的控制,且油气具有近源成藏、短距离运移的特点。

Detailed analyses of crude oils and source rock extracts indicate that there are two sets of effective hydrocarbon source rocks in eastern Pearl River Mouth Basin.Typical crude oil derived from the lacustrine source rocks in the Eocene Wenchang Formation is characterized by abundant C304-methylsteranes but relatively little bicadinane chemicals(T),while the typical crude oil derived from Oligocene Enping Formation features in high content of bicadinane chemicals(T)and relatively low content of C30 4-methylsteranes with high Pr/Ph.The chemical compositions of most crude oils coincide with the mixed features of these two source rocks but do not match those unknown source rocks.The comparison of oil sources shows that the crude oils of Xijiang 24-3 and Xijiang 24-1 mainly derived from the source rocks in Xijiang-24 Wenchang and Enping Formations.The chemical composition of crude oils is determined by the source rocks combination in sags.The oil and gas in the basin features in hydrocarbon accumulation near the source rocks and short distance migration from them.