Abstract:

There are abundant faults with different sizes in Sanzhao depression, Songliao basin. Predecessors who think that the large faults were main migration pathway for Fuyang and Putaohua oil layers, neglect the petroleum significance of small faults. There are a lot of small faults in the Cretaceous of Sanzhao depression, characterized by polygonal planform geometry and small distribution length, small fault throw and big angle of dip. So it is suggested that the small faults are Polygonal fault systems(PFS). In the plane, PFS distributed in the whole depression; while in the vertical, it distributed both in Fuyang and Putaohua oil layers. And PFS played a significant role during the accumulation of reservoirs. PFS, as the main migration pathway of Fuyang oil layer, have controlled the distribution of the oil layer, and widely-developed PFS are the main reason for continuous distribution of oil layer. Large faults and PFS are the main migration pathway of Putaohua oil layer, among which PFS played a bypass role in hydrocarbon migration of Putaohua oil layer and has some influence on the distributiion of Putaohua oil layer.

Key words: polygonal fault systems, petroleum migration, Putaohau oil layer, Fuyang oil layer, Sanzhao depression, Songliao basin