大民屯凹陷高凝油全烃地球化学特征

Total Hydrocarbon Geochemical Characteristics of High Pour Point Oil in Damintun Sag

以原油全烃气相色谱分析技术为工具,从正构烷烃和轻烃化合物两方面对大民屯凹陷高凝油进行成熟度、沉积环境、母质类型等方面的地球化学特征研究。正构烷烃分析认为高凝油为后峰单峰型分布,碳数范围大,主峰碳大,略呈奇碳优势,轻重比(∑nC21-/∑nC22+)在0.79~0.91之间,姥植比(Pr/Ph)介于1.49~2.28,高凝油为成熟烃源岩的产物,形成于弱还原的环境中,有机质输入以陆生生物为主要来源,具有高等植物蜡的特征。轻烃化合物中,C5~C7轻烃馏分以正构烷烃为主,含有一定的环烷烃,C7轻烃化合物中正庚烷含量最高,甲基环己烷次之,推测来源于腐泥型母质烃源岩,并具高等植物的贡献;K1值符合稳定为1.0的规律,但K2值异常偏低,这可能是高凝油具有陆相有机质来源的一个特点。

This paper took total hydrocarbon chromatographic(THC)analysis as the tool and conducted studies on maturity,sedimentary environment,parent material type of source rock,and other geochemical characteristics of high pour-point oil from perspectives of overall distribution pattern of normal alkanes and light hydrocarbon compound.The distribution of normal alkanes in high pour-point oil of Damintun Depression shows a single postpeak with a large carbon number range(nC8~nC38)and main peak carbon in nC27;carbon preference index(CPI)and odd-even predominance(OEP)range from 1.05 to 1.06,with no obvious OEP;∑21-/∑22+ranges from 0.79 to 0.91;the Pr/Ph ranges from 1.49 to 2.28,showing pristane prevalence;the crude oil is the outcome of mature source rock and is formed in the environment of weak reduction,and the main source of organic material input is terrestrial organism dominated by higher plant.As for light hydrocarbon compound,C4~C7 light hydrocarbon fraction of high pour-point oil sample is dominated by normal alkanes and contains certain naphthenes;in C7 light hydrocarbon compound,the content of heptane is the highest,followed by methylcyclohexane,which is speculated originating from source rock with sapropelic parent material with characteristics of source rock with terrigenous parent material.K1 of the sample is stable,while K2 is abnormally low,which is considered as one of the features of high pour-point oil with terrigenous organic material source.