Abstract: In view of various aspects of source bed, reservoir rock, caprock, barrier and structural features, this pa- per studied the oil-gas migration and accumulation of petroleum system of Shahejie formation in Chexi sag of Bohai bay basin. Furthermore, combining the analysis of nose structure and arch-shape faults in the depression as well as the distribution of sand bodies, we also discussed the oil-gas distribution. The author integrate the source rock, reservoir rock, caprock and trapment as an unified basic pool-forming unit—oil-gas pool forming unit. Then according to characteristics of geological structure, it was subdivided into Ⅰ,Ⅱ, Ⅲ classes. It is considered that in petroleum systems, there exists a principal orientation of oil-gas migration and accumulation, namely the oil-gas distribution and formation unit which is dominated by oil-gas unit. It is represented by various kinds of oil-gas pool distribution patterns, including radiating distribution form, circular distribution form. And combined distribution the above two forms dominate the various types of oil and gas distribution. It revealed the internal relations to a certain degree of source rock of fault-depression basin, sandbody distribution, structures characteristics with the formation of oil-gas pools.

Key words: source rock, oil and gas generating, oil and gas accumulating, oil and gas migration, oil and gas entrapment, nose-like structure