南八仙构造油气成藏模式及其对柴北缘勘探的启示

柴北缘为柴达木盆地北部一个以侏罗系生烃、第三系为主要储集层的含油气系统。南八仙构造是柴北缘一个具有代表性的三级构造。该构造反映出柴北缘分别在早第三纪和晚第三纪受到不同方向、不同性质的区域挤压或压扭作用,并分别形成基底卷入型和盖层滑脱型两种不同构造样式的断层。基底卷入断层是下第三系储层形成油气藏必不可少的油源通道;晚第三纪滑脱型断层则对下第三系油气藏起破坏作用,并导致上第三系次生油气藏的形成。原油性质、储层包裹体均一化温度和包裹体正构烷烃分布都证明下第三系储层存在早晚两期油气注入,上第三系储层则为晚期油气注入。南八仙构造的油气成藏模式说明,加强断层活动史和封闭史研究对柴北缘油气评价有重要意义;与上第三系相比,下第三系的油气藏形成条件更有利。

POOL-FORMING MODEL OF HYDROCARBON IN NANBAXIAN STRUCTURE AND ITS IMPLICATION TO THE EXPLORATION OF THE NORTHERN MARGIN OF THE QAIDAM BASIN

The northern margin of the Qaidam Basin is a petroliferous system in the northern part of the basin with the Jurassic source rock and the Tertiary master reservoir. Nanbaxian structure is a representative tertiary structure on the northern margin of the Qaidam Basin. The structure reflects that the northern margin of the Qaidam Basin was subjected to regional compression or compresso shearing of different direction and different characteristics in the Paleogene and Neogene, and formed basement involved and mantle detached two different tectonic patterns of faults respectively. The basement involved fault is an essential passage of oil source to form oil and gas pools in the Lower Tertiary reservoir, and the Late Tertiary mantle detached fault on the other side plays a destructive role to the Lower Tertiary oil and gas pools and results in the formation of the Upper Tertiary secondary oil and gas pools. The properties of crude oil, the homogenization temperature of reservoir inclusions and the n alkane distribution of inclusions all show that the Lower Tertiary reservoir has early and late two stages of hydrocarbon injection and the Upper Tertiary reservoir has only late staye hydrocarbon injection. The pool forming model of hydrocarbon in Nanbaxian structure suggests that the enhancement of study on the moving history and sealing history of faults have important significance to the evaluation of hydrocarbon on the northern margin of the Qaidam Basin. Compared with the Upper Tertiary, the Lower Tertiary has more advantageons conditions to form oil and gas pools.