Abstract:

Abstract: Based on data from drilling,logging,seismic and lab,we make a study of the Fuyang oilbearing interval in Songliao Basin by using theories of continental sequence stratigraphy,sedimentary geology and hydrocarbon accumulation.The Fuyang oilbearing interval in Songliao Basin is a lowporosity and lowpermeability reservoir of fluvial facies.The overlapping mudstone of lacustrine facies in the 1^st member of the Cretaceous Qingshankou Formation is both source rock and regional seal,and therefore hydrocarbons generated in the upper source rocks migrated downward and accumulated in the lower reservoirs.Oilsource correlation shows that average distance of downward vertical migration of hydrocarbons is 300 m with the longest distance of 500 m.At the end of the Mingshui Formation deposition,stress field inversion resulted in various faults cutting through source rocks and the Fuyang oilbearing interval and many fractures inside the source rocks and reservoirs.At the same time,source rocks reached the peak of hydrocarbon generation.Driven by tectonic stress and overpressure due to hydrocarbon generation,the hydrocarbons migrated downward along the faults and fractures and accumulated in the Fuyang oilbearing interval.Hence the major period for hydrocarbon accumulation is the late period of the Mingshui Formation deposition.With favorable reservoir quality,meandering river point bars are major reservoirs for oil and gas.The existence of mudstone seals of shallow lacustrine facies leads to the formation of two sets of oilbearing intervals.Oil pools mainly developed in the Fuyang oilbearing interval which was close to the oil source and have a uniform oilwater contact in the basin.High mature source rocks in the 1^st member of the Qingshankou Formation determine that oil pools are mainly distributed in the central depression zone.Relatively low nettogross ratio leads to the predominance of lithlogic oil pools in the Fuyang oilbearing interval.