渤海湾盆地渤中19⁃6凝析气田高蜡凝析油地球化学特征及成因分析

Geochemical Characteristics and Origin of High-wax Condensate in Bozhong 19-6 Condensate Gas Field,Bohai Bay Basin

渤海湾盆地渤中19-6凝析气田凝析油以高含蜡为特征,综合前人研究成果和油气地球化学资料对渤中19-6凝析气田高蜡凝析油特征和成因进行了分析。结果表明,研究区凝析油具有低密度、低黏度、低沥青质和胶质、高蜡和高凝固点的物性特征,其低碳数与中—高碳数正构烷烃含量相当,C_(1-8)轻烃组分以正构烷烃和环烷烃为主,C_(27)、C_(28)和C_(29)规则甾烷呈“L”字型分布,C_(30)4-甲基甾烷含量较高、伽马蜡烷含量中等—低,3+4—甲基双金刚烷含量较低,主要为沙河街组三段烃源岩成熟阶段的产物。高蜡凝析油的形成主要受控于烃源岩母质类型和相控混溶的凝析气形成机制。研究区烃源岩有机显微组分以腐泥无定形体和腐殖无定形体为主,为高蜡凝析油的形成提供了充足的物质基础。相控混溶的凝析气成因机制为高蜡凝析油的形成与保存创造了良好的外部条件。

The condensates of Bozhong 19-6 gas condensate field in the Bohai Bay Basin feature high wax content.This study discusses the characteristics and genesis of condensates with high wax content at this location,based on previous research and geochemical data.The results show that the condensate oil has the physical properties of low density,low viscosity,low asphaltene and resin content,high wax content and high freezing point.In the condensate oil,the content of n-alkanes with low carbon components is equivalent to that with medium and high carbon number,and light hydrocarbon components of C_(1⁃8) are mainly n-alkanes and cycloalkanes.The distribution of C_(27),C_(28) and C_(29) regular steranes is L-shaped.The condensate oil contains high 4-methyl steranes,medium and low gammacerane and low 3+4-methyl diamantane.The condensate oil is the product of mature source rocks in Member 3 of the Shahejie Formation.The high wax content in the condensate oil is mainly controlled by organic matter type and phasecontrolled miscibility.The organic macerals in source rocks in the study area are mainly sapropelic amorphous and hu⁃mic amorphous,which provide a sufficient material basis for the formation of high-wax condensate;and the formation mechanism of phase-controlled miscibility provides favorable external conditions for the formation and preservation of high-wax condensate.