辽西低凸起JZ25-1S太古界潜山原油地球化学特征及来源分析

Geochemical characteristics and source analysis of crude oil from Archean buried hill JZ25-1S in Liaoxi Low Uplift

为探讨辽西低凸起JZ25-1S太古界潜山原油的地球化学特征及其来源,分析了太古界潜山原油物性、族组分、稳定碳同位素、生物标志化合物分布特征并与古近系原油地球化学特征进行对比研究。该区古近系沙河街组二段和太古界潜山原油主要为轻质和中质原油;族组分具有中等饱和烃、高芳香烃、高非烃+沥青质的特征;原油碳同位素分布在-26.2‰^-24.4‰,族组分同位素分馏效应小;色谱曲线明显见到生物降解形成的“鼓包”,单高峰—后峰态为主,Pr/Ph一般在1.3左右,Pr/nC17、Ph/nC18均为高值;原油的甾萜烷特征表现出伽马蜡烷丰度较高、C27重排甾烷和4-甲基甾烷含量中等,甲藻甾烷含量低,规则甾烷C27、C28、C29指纹呈不对称的偏“V”或“L”型分布。但JZ25-1S-4D井和JZ25-1-10D井太古界原油与上述原油特征存在较大的差异。JZ25-1S地区古近系和太古界潜山原油主体为辽西凹陷沙三段、辽中凹陷沙一段烃源岩混合来源,其母质来源于具有一定盐度的弱还原环境,以藻类等浮游动植物输入为主,且原油成熟度较高,受生物降解严重。JZ25-1S-4D井和JZ25-1-10D井太古界潜山原油来源于辽西凹陷沙三段烃源岩,为淡水弱还原环境,原油成熟度高,受生物降解较弱。

The physical properties,group composition,stable carbon isotope,and biomarker compound distribution characteristics of crude oil in the Archean buried hill were studied and compared with the geochemical characteristics of Paleogene crude oil,in order to discuss the geochemical characteristics and sources of crude oil from the Archean buried hill JZ25-1S in the Liaoxi Low Uplift.The crude oil from the second member of the Paleogene Shahejie Forma⁃tion and the Archean buried hill in this area are mainly light and medium crude oil.The oil has medium saturated hydrocarbon,high aromatic hydrocarbon,high non⁃hydrocarbon and asphaltene contents.The carbon isotopes of the crude oil are distributed between-26.2‰and-24.4‰,and the isotopic fractionation among group components is small.The chromatographic curve clearly shows the“bulge”formed by biodegradation,the single peak and post⁃kurtosis state is dominant,the Pr/Ph value is generally around 1.3,and the Pr/nC17,Ph/nC18 values are both high.The sterane characteristics of crude oil show a high gammacerane abundance,the C27 rearranged sterane and 4⁃methyl sterane contents are medium,the dinostane content is low,and the regular sterane C27,C28,C29 fingerprints are partial“V”or“L”shaped.However,the characteristics of Archean crude oil from wells JZ25⁃1S⁃4D and JZ25⁃1⁃10D are quite different from the above⁃mentioned crude oil.Comprehensive analysis suggests that the main body of crude oil from the Paleogene and Archean buried hills in the JZ25⁃1S area is a mixture from the Es3 member of the Liaoxi Sag and the Es1 member of the Liaozhong Sag.Its parent material comes from a weakly reducing environment with moderate salinity and is mainly derived from algae and other phytoplankton.The crude oil has a high degree of maturity and is severely biodegraded.The Archean buried hill crude oil from wells JZ25⁃1S⁃4D and JZ25⁃1⁃10D is derived from the Es3 member source rock in the Liaoxi Sag,which was deposited in a weakly reducing freshwater environment with high maturity and weak biodegradation.