渤海湾盆地青东凹陷古近系原油地球化学特征及油源分析

摘要

渤海湾盆地济阳坳陷青东凹陷存在常规原油和生物降解油.选取新参数β-胡萝卜烷/(2×C29藿烷)、伽马蜡烷/(2×C29藿烷),三环萜烷系列参数(2×C24四环萜烷)/(C26三环萜烷)、(2×C19)/(C28+C29)三环萜烷以及艹屈/菲,结合C29 4-甲基甾烷及碳同位素特征等,将该区原油划分为Ⅰ、Ⅱ、Ⅲ和Ⅳ等4类,烃源岩划分为A、B1和B2 等3类.Ⅰ类原油来自青东凹陷中北部深洼的沙三下亚段成熟烃源岩,Ⅱ类原油来自凹陷南部沙四上亚段烃源岩,Ⅲ类原油来自中北部洼陷的沙四上亚段烃源岩,Ⅳ类原油来自青南洼陷沙四上亚段烃源岩,而青东8井原油应有青东凹陷南部烃源岩的贡献.%Biodegraded oils have been discovered in the Qingdong Sag, Jiyang Depression, Bohai Bay Basin.On the basis of the geochemical characteristics of source rocks and crude oils, the less affected C29 hopane, is chosen to calculate biomarker parameters, including β-carotane/(2×C29hopanes), gammacerane/(2×C29hopanes).The tricyclic terpane parameters (2×C24tetracyclic terpane)/(C26 tricyclic terpanes), (2×C19)/(C28+C29) tricyclic terpanes and chrysene/phenanthrene, combined with 4-methylsteranes and carbon isotopes.Crude oils in the Qingdong Sag were divided into 4 types (Ⅰ, Ⅱ, Ⅲ, Ⅳ), while source rocks were divided into 3 types (A, B1, B2).Crude oils of type I derived from mature source rocks (type A) in the lower part of the third member of Shahejie Formation in the northern part of the sag.Crude oils of type Ⅱ were sourced from rocks (type B2) in the upper part of the fourth member of Shahejie Formation in the southern part of the sag.Crude oils of type Ⅲ were derived from type B1 source rocks in the upper part of the fourth member of Shahejie Formation in the central and northern parts of the sag.Crude oils of type Ⅳ were sourced from rocks in the upper part of the fourth member of Shahejie Formation in the Qingnan Sag.Oils in well QD-8 partially originated from source rocks in the southern part of the Qingdong Sag.