珠江口盆地油气分带性及其控制因素

Hydrocarbon zonation and its control factors in Pearl River Mouth basin

珠江口盆地油气分布存在明显的分带性,浅水区珠一、珠三坳陷以油为主,油气主要来源于始新统文昌组中深湖相烃源岩,其次来源于下渐新统恩平组沼泽相烃源岩;而深水区珠二坳陷以天然气为主,油气主要来源于恩平组沼泽相烃源岩和渐新统海相烃源岩。珠江口盆地油气分带性主要受控于烃源岩的有机质类型及热演化程度。珠一、珠三坳陷文昌组中深湖相烃源岩有机质类型主要为Ⅱ1型,为倾油型烃源岩,而珠二坳陷恩平组煤系烃源岩和渐新统海相烃源岩有机质类型主要为Ⅱ2—Ⅲ型,为倾气型烃源岩,所以烃源岩有机质类型的差异是珠江口盆地油气分带的内在因素。珠江口盆地总体具有"热盆"属性,但深水区比浅水区更热,对于相同层系的烃源岩,深水区烃源岩的热演化程度明显高于浅水区,所以烃源岩热演化程度的差异是珠江口盆地油气分带的外在因素。

There is a clear zonation of oil and gas distribution in Pearl River Mouth basin （PRMB）, with Zhu I and Zhu III depressions in shallow wa- ter predominated by oil from the main source rocks of middle-deep lake facies in Wenchang Formation and the subsidiary source rocks of paludal facies in Enping Formation, and Zhu II depression in deep water predominated by gas from the source rocks of paludal facies in Enping Formation and Oligo- cene marine facies. This hydrocarbon zonation is primarily controlled by organic type and thermal maturation of the source rocks. In Zhu I and Zhu III depressions, the source rocks of middle-deep lake facies in Wenehang Formation are prone to oil due to their predominated organic matter of Type II1 ~ and in Zhu ]] depression, the source rocks of paludal facies in Enping Formation and Oligocene marine facies are prone to gas due to their predomi- nated organic matter of Type II2-III. Therefore, the difference in organic type of the source rocks is an intrinsic control factor over the hydrocarbon zonation. In general, PRMB is a ＂hot＂ basin, but its deep water is ＂hotter＂ than its shallow water, re sulting in the much higher maturation of the same- formation source rocks in the deep water than in the shallow water. Thus, the difference in matura tion of the source rocks is an extraneous control factor over the hydrocarbon zonation in PRMB.