塔河油田白垩系原油地化特征与成因类型

Geochemical characteristics and genetic types of Cretaceous oils,Tahe oilfield

利用气相色谱和气相色谱-质谱联用仪对采自塔河油田白垩系油藏的12件原油进行了生物标志物分析,系统研究了原油的地球化学和原油及族组成碳同位素特征.结果表明:白垩系原油中正构烷烃系列的碳数分布范围为nC10~nC35且呈前峰型单峰态分布,以nC15或nC16为主峰碳数、C21TT/C23TT值分布范围为0.51~0.56、甾烷质量分数C27>C28<<C29,C29/C30藿烷值分布范围为0.55~0.69、原油碳同位素值分布范围为-31.94‰^-30.00‰.东、西部白垩系原油在部分分子地球化学指标上存在差异.东部原油Pr/Ph>1.4,西部原油Pr/Ph<1.2;东部原油二苯并噻吩质量分数为50%~70%,西部原油二苯并噻吩质量分数>80%;东部原油C30重排藿烷/C30藿烷值为0.20~0.23,西部原油C30重排藿烷/C30藿烷值为0.08~0.11.因此,白垩系原油与奥陶系原油具有共同的特征,即低密度、低含硫量、完整的正烷烃系列且以低分子量轻烃为主、C21/C23三环萜烷值<1、规则甾烷呈不对称"V"型分布、高C29/C30藿烷值、高二苯并噻吩含量、低碳同位素值,两者具有统一的油源,为同一成因类型.塔河油田白垩系东部6口井的原油与西部6口井原油分别属于不同的组群,造成东西部原油细微分子地球化学差异的原因可能是地层浸染或者气侵等次生作用.

Biomarkers in twelve Cretaceous oils of Tahe oilfield were analyzed using gas chromatography and gas chromatography-mass spectrometry,and the geochemical characteristics and carbon isotopic value of oils were systematically studied.The results show that the n-alkanes carbon number distribution from nC10 to nC35 have a single peak with nC15 or nC16 dominating,the C21TT/C23TT range is 0.51-0.56,the C27 regular steranes content is much less than that of C29 but greater than that of C28,the C29/C30 hopane value range is 0.55-0.69,the carbon isotope value range is-31.94‰——30.00‰.The cretaceous oils have some geochemical differences between East and west.Pr/Ph in eastern Oils is higher than 1.4 and less than 1.2 in western oils.The Dibenzothiophene content range is 50%-70 % in eastern oils and is higher than 80% in western oils.The C30 diahopane/C30 hopane range is 0.20-0.23 and 0.08-0.11 in eastern oils and western oils respectively,therefore,both the Cretaceous and Ordovician oils have common characteristics.For example low density,low sulfur content,a complete series of n-alkanes with low molecular weight,hydrocarbon domination,C21/C23 lower than 1,asymmetrical ＂V＂ distribution-type of regular steranes,higher C29/C30 hopane values,higher dibenzothiophene content and low carbon isotope values.Both the Cretaceous oils and the Ordovician oils have the same source and genetic type.The eastern crude oils are different from western oils in some different groups.For the Cretaceous crude oils between east and west,subtle geochemical differences are caused by stratigraphic dip or gas invasion and other secondary effects.