Abstract: The evolution history, oil source, filling time and carrier system in Babei-I trap of northern margin of Qaidam basin are analyzed. It is indicated that from Late N₁ to Early N₂, oil generated from Middle Jurassic hydrocarbon source rocks in Gaqiu sag migrated to the shallow layer (<1 000 m) of Well Mabei-1 within Mabei-I trap and Mabei-III trap. In the period of Middle N₂, the source rocks with higher maturity of Middle Jurassic in Saishiteng sag originated expulsion of hydrocarbon followed by migrating into the deep layer (>1 000 m) of Well Mabei-1. In the Late Himalayan movement, the whole Mahai swell was uplifted, featuring fixed traps and shallower reservoirs. The model of hydrocarbon accumulation in Mabei-I trap could be described as that the drape-like structure was formed on the paleo-uplift of basement in the period of Yanshan movement, the traps were evolved successively and formed by the end of Yanshan period. Also, there exist two-source and two-stage hydrocarbon accumulations in this area.

Key words: Qaidam basin, trap, hydrocarbon accumulation, mechanism, model