Petroleum accumulation conditions of Damoguaihe Formation in Urxun—Beier Sags, Hailaer Basin

The petroleum accumulation conditions of Damoguaihe Formation in the Urxun—Beier Sags of the Hailaer Basin were studied with stratigraphic,tectonic and accumulation system theories.The fractures in the study area experienced 3 stages of deformation including the extension during Tongbomiao and Damoguaihe periods,the strike-slip during Yimin period and the strong inversion during Qingyuangang and the late Paleogene periods.Damoguaihe Formation was divided into 3 third-grade sequences and 15 sand layers.Different stages controlled different sedimentary evolution processes.The crude oil in Damoguaihe Formation came from Nantun Formation and was closely related to the first member of Nantun Formation.There existed 2 ways of hydrocarbon migration.1)When the fault displacement was over 300 m,the source rocks in Nantun Formation connected with the reservoirs in Damoguaihe Formation,resulting in side-generating and side-reserving reservoirs.2)The hydrocarbon in Nantun Formation migrated upwards into Damoguaihe Formation,and then moved laterally for a short distance,forming lower-generating and upper-reserving reservoirs.The reservoirs in the region were classified into 4 types: tectonic,lithologic,stratigraphic and lithologic—tectonic.