西湖凹陷西部斜坡带原油来源

Crude oil source in the western slope zone of Xihu sag

原油来源分析是确定油气勘探方向的重要依据。利用有机地球化学分析手段,分析了西湖凹陷西部斜坡带原油和烃源岩特征,通过生物标志物谱图和生物标志物参数的对比,结合原油与烃源岩分布特征,确定了西湖凹陷西斜坡不同区原油的来源。结果表明:(1)研究区原油总体上富含指示陆源高等植物输入的生物标志物,但平北地区原油碳同位素重,二萜类丰富,规则甾烷以C29甾烷为主;平湖地区原油碳同位素较轻,二萜类含量较高,且具有较低的伽马蜡烷;黄岩-天台地区原油碳同位素轻,二萜类含量低,规则甾烷以C29甾烷为主,同时C27甾烷的含量也较高。(2)研究区发育煤系烃源岩(包括煤和炭质泥岩)和暗色泥岩两类烃源岩。煤系烃源岩富含来源于裸子植物的异海松烷类和蕨类植物的16β(H)-扁枝烷,从平北到黄岩-天台地区的煤系烃源岩中16β(H)-扁枝烷含量增加;暗色泥岩二萜类含量低,16β(H)-扁枝烷相对于降异海松烷占优势,且从平北到黄岩-天台地区暗色泥岩中C27甾烷、16β(H)-扁枝烷增加。(3)平北地区原油主要为煤系烃源岩贡献,平湖地区原油为煤系烃源岩和暗色泥岩混合贡献,且煤系烃源岩的贡献较大,黄岩-天台地区原油主要为暗色泥岩贡献。研究成果对深化西湖凹陷油源认识及油气勘探部署有一定的指导作用。

Crude oil source analysis is a crucial basis for determining the direction of oil and gas exploration.Utilizing organic geochemical techniques,the characteristics of crude oil and source rocks in the western slope zone of Xihu sag were investigated.Subsequently,employing the comparisons of biomarker spectra and biomarker parameters,and combined with the distribution features of crude oil and source rocks,the origin of crude oil in different zones of the western slope of Xihu sag was ascertained.The results indicate that:(1)The crude oil in the study area is generally abundant in biomarkers indicative of terrestrial higher plant origins.However,in Pingbei area,the crude oil exhibits a heavier carbon isotope composition,enriched diterpenoids,and predominance of C_(29)sterane.In Pinghu area,the crude oil displays a lighter carbon isotope composition,higher diterpenoids content,and lower gammacerane.In Huangyan-Tiantai area,the crude oil is characterized by a lighter carbon isotope composition,diminished diterpenoids content,a dominance of C_(29)sterane in regular sterane,and a higher content of C_(27)sterane.(2)The study area develops two types of source rocks including coal measure source rocks(coal and carbonaceous mudstone)and dark mudstone.The coal measure source rocks are enriched in isopimarane derived from gymnosperms and 16β(H)-phyllocladane from ferns.From Pingbei to Huangyan-Tiantai,the content of 16β(H)-phyllocladane displays an increasing trend in the coal measure source rocks,the diterpenoids content is decreasing in the dark mudstones,and 16β(H)-phyllocladane dominates over norisopimarane.Moreover,the content of C_(27)sterane and 16β(H)-phyllocladane increases in dark mudstone.(3)In Pingbei area,the crude oil is mainly contributed by coal measure source rocks,while in Pinghu area,the crude oil is contributed by a combination of coal measure source rocks and dark mudstone,with a significant contribution from coal measure source rocks.In Huangyan-Tiantai area,the crude oil is primarily contributed by dark mudstone.These research findings significantly enhance understanding of the oil source in Xihu sag and provide valuable insights for the deployment of oil and gas exploration.