Abstract: The analysis of fault activity and hydrocarbon migration and accumulation in Fuyang reservoir in northern Songliao basin suggests that this reservoir could not be explained simply by overpressure allowing hydrocarbon to migrate down along faults rather than by the model of intermittent overpressure releasing along faults and episodic counterflow/accumulation, which is the main reason of mature hydrocarbon from Qinshankou source rock migrating down along faults for a long distance. Such a model can not only explain that it is the fault that carried the oil and gas migrating down in condition of overpressure, but also provides theoretic basis for petroleum long-distance counterflow migrating down along faults. Also, it is pointed out that the underlying strata and the deep strata with overpressure in this area are favourable for petroleum exploration.

Key words: Songliao basin, overpressure, petroleum migrating down, fault activity, mechanism, Fuyang reservoir