乌兰花凹陷原油特征及成因

乌兰花凹陷是二连盆地南部新发现的富油凹陷，对乌兰花凹陷原油物理性质和地球化学性质进行了系统的分析以揭示其特征及来源。原油物理性质显示，乌兰花凹陷原油比重（API gravity）介于20.2°~40.0°之间，主体为正常原油。原油生物标志化合物参数表明，不同构造带之间原油特征存在差异，可以划分为两类原油。一类以土牧尔构造带原油为主，具有低姥值比（Pr/Ph）和C₂₁/C₂₃三环萜烷，相对较高的伽马蜡烷/C₃₁藿烷和规则甾烷/C₃₀藿烷的特征，原油主要为烃源岩在成熟阶段早期的产物，主要以藻类来源为主。另一类原油包括赛乌苏和红井构造带原油，具有高姥值比（Pr/Ph）和C₂₁/C₂₃三环萜烷，相对较低的伽马蜡烷/C₃₁藿烷和规则甾烷/C₃₀藿烷，主要为陆源有机质和藻类有机质混合来源，原油具有更高的成熟度。原油碳同位素和正构烷烃单体烃碳同位素表明这两类原油应是一套烃源岩在不同成熟阶段的产物，原油主要来源于南洼槽阿尔善组烃源岩。阿尔善组烃源岩的非均质性和成熟度导致了两类原油的差异。 

Characteristics and origin of crude oils in the Wulanhua sag

The Wulanhua sag is a newly discovered oil-rich sag in the Erlian basin. The physical and geochemical properties of crude oils in the Wulanhua sag were systematically analyzed to reveal the characteristics and origins. The physical properties of crude oils suggest that the API gravities range from 20.2° to 40.0°, and most are normal crude oil. The biomarker parameters show considerable variation among the oils from different tectonic units, which can be separated into two crude oil families. Crude oil family-I is dominated by oils from the Tumuer tectonic unit, and characterized by low Pr/Ph and C₂₁/C₂₃ TT, and relatively high gammacerane/C₃₁ hopane and regular sterane/C₃₀ hopane. Crude oil family-I is mostly derived from the algal organic matter at low maturity levels. Crude oil family-Ⅱ consists of oils from the Saiwusu and Hongjing tectonic units, which is characterized by high Pr/Ph and C₂₁/C₂₃ TT, and relatively low gammacerane/C₃₁ hopane and regular sterane/C₃₀ hopane. Crude oil family-Ⅱ is mainly derived from the mixed algal and terrigenous organic matter at higher maturity levels. Carbon isotopic compositions of crude oil and individual n-alkanes indicate that these two crude oil families should be the products of the same set of source rocks at different maturity levels, and likely derived from the K₁ba source rock in the southern sub-sag. The factors controlling differences between the two crude oil families include the heterogeneous source rock and its maturation process.