Abstract: Traditionally, it was believed that the north Shaanxi slop in Ordos basin was a gentle west-tipping monocline. The formation and distribution of Triassic Yanchang reservoir including Chang-6 reservoir were mainly controlled by sedimentary facies, dominated by lithological reservoir, hence the structural factor and others did not play major controlling roles on Yanchang reservoir's formation and distribution in this area. This study shows that the foundation forming Chang-6 reservoir is the delta distributary channel sands, the necessary condition of petroleum enrichment in Chang-6 reservoir is the nose-like uplift setting and the hydrodynamic environment is its important trapping factor. Therefore, Chang-6 reservoir is in various types, dominated by complex reservoirs including structural-lithologic reservoir and structural-hydrodynamic reservoir, sub-dominated by lithologic reservoir.

Key words: Ordos basin, Triassic, distribution, regularity, reservoir type