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.