松江盆地白垩系烃源岩地球化学特征及油源对比

松江盆地白垩系发育大砬子组和长财组两套烃源岩。通过对烃源岩及原油进行常规有机地化分析和生物标志化合物测试，研究了烃源岩和原油的地球化学特征并探讨油源关系。有机地化分析表明，其白垩系烃源岩有机质丰度高，Ⅱ₁-Ⅱ₂型有机质，低成熟-成熟。大砬子组烃源岩生烃潜力大，长财组次之。生物标志化合物分析表明，白垩系部分烃源岩和原油遭受了一定程度的生物降解作用。长财组烃源岩可分为3类，第Ⅰ和第Ⅱ类生烃母质以高等植物为主，为偏氧化的淡水和微咸水沉积，第Ⅲ类伽马蜡烷和β胡萝卜烷含量丰富，为咸水环境沉积。大砬子烃源岩为咸化的还原环境沉积，生烃母质为混合源。经油源对比表明，长财组下段原油来源于长财组第Ⅰ类烃源岩，长财组上段原油来源于第Ⅱ类烃源岩，而偏还原的大砬子组原油来源于大砬子组上段烃源岩。

Geochemical characteristics of Cretaceous source rocks and oil-source correlation in the Songjiang Basin

Two sets of Cretaceous source rocks,Dalazi and Changcai Formation,develop in the Songjiang Basin.In this study,we discussed the geochemical characteristics of source rocks and crude oil and the oil-source correlation based on the conventional organic geochemical analysis and biomarker compound test on Cretaceous source rocks and crude oil in the basin.The organic geochemical analysis indicates that Cretaceous source rocks are rich in organic matters,with the major organic matter being TypeⅡ₁-Ⅱ₂,and the source rock maturity ranges from low-mature to mature degree.And the Dalazi Formation has the greatest potential of hydrocarbon generation,followed by Changcai Formation.The analysis of biomarker compounds show that some of the Cretaceous source rocks and crude oil are subjected to a certain extent of biodegradation.Besides,source rocks of the Changcai Formation can be divided into three groups:the organic matters of source rock Group Ⅰ and Ⅱ are mainly from higher plants,which are deposited in partially oxidized fresh and brackish water,and source rock Group Ⅲ contains large amounts of gammacerane and β-carrotane,deposited in saline water.Source rocks of the Dalazi Formation are mainly deposited in reductive-brackish water environment,and their parent materials come from mixed sources.The oil-source correlation reveals that the crude oil generated from the Changcai Formation can be divided into two categories:the K₁c¹ oil originates from Group Ⅰ source rock and the K₁c² oil from the Group Ⅱ source rock of the source formation.Meanwhile,the reductive-prone oil from the Dalazi Formation originates from its K₁d²section.