东海盆地西湖凹陷油岩地球化学特征及原油成因来源

Geochemical Characteristics of Oil and Source Rock,Origin and Genesis of Oil in Xihu Depression,East China Sea Basin

东海盆地西湖凹陷具有大量的原油资源,但对于原油成因讨论较少.采集西湖凹陷多个油样和岩样,利用气相色谱和傅里叶红外光谱等手段,全面分析了该区烃源岩和原油的地球化学特征,综合讨论了原油来源以及凝析油和高蜡轻质油的成因.研究结果表明,平湖组煤系源岩均处于热演化的成熟阶段,其中碳质泥岩和煤岩以陆源生物为主要生源,其干酪根类型为Ⅲ型,暗色泥岩则具有陆源生物和水生生物双重生源贡献,其干酪根类型Ⅱ-Ⅲ型,同时碳质泥岩和煤的生油潜力远高于泥岩.原油主要为凝析油和轻质油,凝析油具有低密度、低蜡等"六低一高"的特点,轻质油具有高蜡特质,而且轻烃组分有明显差异.生标参数显示大部分原油为腐殖型,少部分原油表现出具有腐殖和腐泥母质的特点,同时该区原油均处于中等成熟阶段.油油对比和油岩对比表明大部分油来自平湖组碳质泥岩和煤岩,具有典型Ⅲ型腐殖油的特征;少部分油来自暗色泥岩,具有Ⅱ-Ⅲ型油的特征(总体上仍偏腐殖型).凝析油和轻质油的物性及轻烃组分的差异与源岩母质无关.凝析油是干酪根在成熟演化阶段生成的原油遭受蒸发分馏作用的结果,高蜡轻质油除了是"蒸发分馏作用"的残余油外,还有部分是"混合作用"的结果.

There are plenty of oil in Xihu depression of East China Sea basin,however,few scholars pay attention to the origin and genesis of oil.The samples of source rocks and oil were measured by gas chromatography and Fourier transform infrared spectroscopy （FTIR）,and the origin of oil and genesis of condensate and high-wax light oil are discussed based on the analysis of geochemical characteristics.The results suggest that coal measure source rocks of the Pinghu Formation are at the mature stage of thermal evolution.Carbonaceous mudstone and coal mainly came from terrestrial organism,with kerogen type Ⅲ. Dark mudstone mainly came from both terrestrial organism and aquatic organism,with kerogen type Ⅱ-Ⅲ.Genetic potential of carbonaceous mudstone and coal is significantly higher than that of mudstone.The crude oil is mainly divided into condensate with low density and wax and high-wax light oil,and light hydrocarbon displays obvious different compositions.Most of the oil is of humic type with some oil being both humic and sapropelic.Oil is at the medium mature stage.Most oil is derived from carbonaceous mudstone and coal in the Pinghu Formation,whereas only a small amount of oil is derived from dark mudstone.Physical properties of condensate and light oil and their difference of light hydrocarbon composition are unrelated with source rocks.Condensate was produced under the evap-oration fractionation effect and from the oil which had been generated from the kerogen at the mature stage.High-wax light oil is resid-ual oil from evaporation fractionation effect,and some oil has experienced mixing.