渤东凹陷北部烃源岩地球化学特征与油源对比

探讨渤海湾盆地渤东凹陷北部多套烃源岩的生烃潜力及其生烃贡献。通过烃源岩有机碳含量测试及岩石热解分析,结果显示东三段、沙一+沙二段、沙三段均发育优质烃源岩,3套烃源岩的干酪根均以Ⅱ1-Ⅱ2型为主,主要处于低成熟阶段。烃源岩GC-MS测试表明它们形成于不同的沉积环境,母质来源各异,表现出明显不同的生物标志物组合特征。东三段以较低伽马蜡烷/C₃₀藿烷(<0.11)、较低ETR(<0.3)和较高C₁₉TT/C₂₃TT(>0.5)为特征,沉积于缺氧-低氧的淡水湖泊环境,具有较多的陆源有机质输入。沙河街组以较高伽马蜡烷/C₃₀藿烷(>0.11)、较高ETR(>0.3)和较低C₁₉TT/C₂₃TT(<0.5)为特征,沉积在缺氧的弱咸化湖泊环境,陆源有机质输入较少。沙三段的沟鞭藻贡献较大,以高4-MSI(>0.17)和高TDSI(>0.35)为特征,与东三段、沙一+沙二段存在明显差异。基于生物标志物参数的主成分分析将原油划分为3类油族:油族A来源于沙三段烃源岩;油族B来源于东三段烃源岩;油族C主要来源于沙一+沙二段烃源岩,次为东三段烃源岩。

Geochemical characteristics and oil-source correlation of source rocks in northern Bodong Sag,Bohai Bay,China

The hydrocarbon generation potential and contribution of multiple sets of source rocks in the northern Bodong Sag,Bohai Bay Basin are discussed by measurement of organic carbon content of source rocks and rock pyrolysis analysis.The results show that the third member of the Oligocene Dongying Formation(E₃d³),the first to second(E₂s¹⁺²)and third(E₂s³)members of the Eocene Shahejie Formation all develop high quality source rocks,and the kerogen of the three sets of source rocks is mainly typeⅡ₁-Ⅱ₂,which is mainly in low maturity stage.GC-MS analysis show that the source rocks were formed in different sedimentary environments and their parent materials came from different sources,showing obviously different biomarker combinations.The E₃d³ is considered to be deposited in anoxic-hypoxic freshwater lakes with more terrigenous organic matter input,evidenced by lower gammacerane/C₃₀ hopane(<0.11),lower ETR(<0.3)and higher C₁₉TT/C₂₃TT(>0.5),and the Shahejie Formation is thought to be deposited in anoxic alkaline-alkaline lakes with less input of terrigenous organic matter,evidenced by higher gammacerane/C₃₀ hopane(>0.11),higher ETR(>0.3)and lower C₁₉TT/C₂₃TT(<0.5).The contribution of dinoflagellates in the E₂s³ is higher than that in the E₃d³ and the E₂s¹⁺²,which is characterized by high 4-MSI(>0.17)and TDSI(>0.35).Based on the principal component analysis of biomarker parameters,the crude oil in the study area can be divided into three oil groups:Oil group A comes from the source rock of E₂s³;Oil group B comes from E₃d³;and the main source of oil group C is E₂s¹⁺²,and the secondary source is E₃d³.