普光气田沥青地球化学特征及成因

doi:10.11743/ogg20060308

摘要/Abstract

摘要：

系统的地球化学分析表明,普光气田飞仙关和长兴组气藏沥青为古油藏原油经热裂解成气的残留物。其有机元素组成以贫氢、富氧、富硫为特征,属高热演化且受硫酸盐热化学还原作用影响的焦沥青类。它们的碳同位素变化在-25.60‰～-27.78‰之间,与本区上二叠统烃源岩干酪根相当(-26.50‰～-29.20‰),两者具有成因关系。这些沥青的饱和烃中正烷烃系列碳数分布完整,没有遭受过严重生物降解作用的迹象。它们呈植烷优势,Pr/Ph值小于1.0;甾烷系列中C27化合物占优势,检出C₃₀和C₂₆甾烷;萜烷中三环萜烷丰富,伽马蜡烷含量较高。这表明有机质来源以水生生物为主,是在还原环境中沉积的海相烃源层。沥青的芳烃组成独特,富含四、五环芳烃化合物,且以萤蒽、芘、屈和苯并萤蒽等无烷基取代的母体芳烃化合物为主,反映出沥青裂解成气过程中的有机质芳构化作用。芳烃分布模式及甲基菲指数显示,这些沥青已达高演化阶段,相当的镜质体反射率在2.0以上。

关键词: 有机元素, 碳同位素, 生物标志物, 芳烃, 沥青, 普光气田, 四川盆地

Abstract:

Systematic geochemical analyses show that the reservoir bitumen in Feixianguan and Changxing Formations in Puguang gas pool are residuals of the original oil in fossil oil pools after they have been thermally cracked into gas.The organic elementary compositions of the bitumen are characterized by poor hydrogen and rich oxygen and sulfur,suggesting that it is of pyrobitumen as a result of high maturity and TSR.The bitumen has δ¹³C values ranging from-25.60‰ to-27.78‰ and fits isotopically with kerogen in the Upper Permian source rocks(-26.5‰ to-29.2‰),indicating a genetic relationship between them.The n-alkanes with a complete range of carbon number are observed in the saturated hydrocarbons of the bitumen and no evidences of severe biodegradation occur.They exhibit a phytane predominance with Pr/Ph ratios less than 1.0; predominance of C₂₇ compounds occur in the steranes with detectable C₃₀ and C₂₆ steranes;and the terpanes are characterized by abundant tricyclic terpanes and gammacerane.All these indicate that aquatic organism-dominated marine source rocks have been deposited in a reducing environment.As a result of aromatization of organic matter during the thermal cracking of original bitumen into gas,the aromatic hydrocarbons in the bitumen are characterized by abnormally abundant tetra-and penta-cyclic compounds,and predominated by parent aromatic compounds without alkyl chain,such as fluoranthene,pyrene,chrysene, benzofluoranthene etc.The distribution pattern and MPI index of aromatic hydrocarbons reveal a high thermal evolution for the bitumen with a corresponding R_o value of over 2.0%.

Key words: organic element, carbon isotope, biomarker, aromatic hydrocarbon, bitumen, Puguang gas pool, Sichuan basin

中图分类号:

TE125.2

蔡勋育,朱扬明,黄仁春. 普光气田沥青地球化学特征及成因[J]. 石油与天然气地质, 2006, 27(3): 340-347. doi: 10.11743/ogg20060308 Cai Xunyu,Zhu Yangming,Huang Renchun. Geochemical behaviors and origin of reservoir bitumen in Puguang gas pool[J]. Oil & Gas Geology, 2006, 27(3): 340-347. doi: 10.11743/ogg20060308

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