南堡凹陷混源油分布与主力烃源岩识别

南堡凹陷油气源尚不清晰.首次采用单体烃碳同位素、结合生物标志物对全凹陷范围的原油和烃源岩进行了精细地球化学研究.分析表明, 拾场次洼沙三段烃源岩(Ⅰ类)发育高丰度的4-甲基甾烷与硫芴系列、贫伽玛蜡烷, 单体烃碳同位素为"斜直线型", 相关原油分布于高柳深层; 南堡凹陷南部沙二+三段源岩(Ⅱ类)伽玛蜡烷较发育, 但4-甲基甾烷不太发育, 其他特征类似于Ⅰ类源岩, 相关原油发现于潜山; 南堡凹陷沙一段-东三段烃源岩(Ⅲ类)富含重排甾烷与孕甾烷系列, 单体烃碳同位素较轻且近"W"型, 相关原油主要分布于南堡4、5号构造带.发现南堡油田1、2号构造带、老爷庙、高柳中浅层原油具有界于Ⅱ、Ⅲ类源岩(及相关原油)间的同位素与生标特征, 系混源油, 定量预测出混源油中沙二+三段源岩的贡献最高达82%.本研究关于Es₂₊₃系南堡凹陷重要的油气源的认识不同于以往研究, 为该区进一步油气勘探提供了重要依据. 

Mixed Oil Distribution and Source Rock Discrimination of the Napu Depression,Bohaibay Basin

The origin of the hydrocarbons in the Napu depression is still not clear. Compound specific carbon isotope of n-alkanes has been utilized, combined with biomarkers to carry out detail geochemical investigations for the oils and source rocks within the whole depression for the first time. The results show that the Tertiary Es₃ rocks (type-Ⅰ) in the Shichang sub-depression are characterized by abundant 4-methyl steranes and dibenzothiophenes but low concentration of gammacerane with a "tilted linear" shape of compound specific carbon isotope distribution. The type-Ⅰ genetic related oil has been discovered in the Tertiary Es₃ interval of Gaoshangpu and Liuzan oilfields. The Tertiary Es₂₊₃ rock (type-Ⅱ) in the south Nanpu depression is featured by a relatively high content of gammacerane while little 4-methyl sterane contained, and it has a similar carbon isotope curve and dibenzothiophene concentration to that of the type-Ⅰ rock. The type-Ⅱ genetic oil has been discovered in the Ordovician burial hills. The Tertiary Es₁-Ed₃ rock (Ⅲ) in the Nanpu depression is distinguished from the others by obviously high content of diasteranes and pregnant series with a relatively lowerδ13C of n-alkane and nearly a "W" shape of carbon isotopic pattern. The type-Ⅲ genetic related oils was discovered in the NP4, 5 tectonic belts. It is observed that the oils in the NP1, 2 tectonic belts, Laoyemiao oilfield and the Tertiary Nm-Es₁ of Gaoshangpu and Liuzan oilfield have intermediate biomarker and isotope characteristics between the type-Ⅱ and type-Ⅲ source rocks and the related oils, indicating mixed sources of the oils derived from both the type-Ⅱ and type-Ⅲ rocks. It is found that the related contribution of the Es₂₊₃ source rocks to the mixed oils is up to 82%. We suggest that the Es₂₊₃ is an important set of source rock in the Nanpu depression, responsible for most of the oils. This result is different from the previous ones that most of the oils in the Nanpu depression were derived from the Es₁-Ed₃ source rocks rather than the Es₂₊₃, which provides essential information for further petroleum exploration of the depression.