准噶尔盆地滴南凸起东段油气成因及来源

Hydrocarbon origin and source in east section of Dinan salient of Junggar Basin

准噶尔盆地滴南凸起东段业已形成规模油藏,原油密度高、粘度大,区域上存在多个生烃凹陷,纵向上存在多套源岩,均具供烃可能性。对原油物性和地球化学特征进行综合分析,指出该区原油碳同位素较轻,C28甾烷丰度较高,轻烃成熟度高于本身和五彩湾凹陷的二叠系烃源岩,原油和储层抽提物饱和烃色谱不完整,轻组分和正构烷烃严重损失,是东道海子凹陷二叠系来源的成熟阶段产物并遭生物降解。对天然气组分的组成和碳同位素特征分析,表明天然气为干气,乙烷碳同位素较重,甲烷碳同位素较轻,并与生物降解油伴生,为原油菌解气与石炭系高—过成熟阶段产物混合的结果。下一步勘探应往东道海子凹陷延伸,构造下倾部位保存条件好,且降解稠油可与致密储层共同封堵形成岩性圈闭,捕获凹陷较高成熟阶段油气。

Oil reservoirs with certain scale have been formed in the east section of Dinan salient, the Junggar Basin. The crude oils are characterized by high density and high viscosity. Several hydrocarbon-generation sags have been found in the region. Many sets of source rocks exist in the longitudinal direction, and they all have hydrocarbon supply- ing possibility. According to the physical and geochemical properties of crude oils, it has been concluded that the crude oils in the study area are characterized by light carbon isotope and high abundance of C28 sterane. The sterane has higher maturity than crude oils themselves and Permian source rocks from the Wucaiwan Sag. The saturated hy- drocarbon chromatograms of crude oils and reservoir extracts are incomplete with severe damage of light components and n-alkanes, which can be explained by biodegradation effect on mature hydrocarbon sourced from Permian of the Dongdaohaizi Sag. The analyses of natural gas composistions and carbon isotopes have indicated that the natural gas is dry gas with heavier ethane carbon isotope and lighter methane carbon isotope, and is associated with biodegraded oil. It is the mixture of crude oil degraded by bacteria and the product of high-over mature stage of Carboniferous. The next exploration direction should be extended to the Dongdaohaizi Sag, and the preserve conditions in the downward inclined part of structure are better. The common plugging of degraded heavy oil and tight reservoir could form litho- logic trap, which is beneficial to capture oil and gas of high mature stage in the sag.