Downfaulted Sequence Stratigraphy and Hydrocarbon Reservoir Forming Characteristics of Wunan Sub-depression in the Hailaer Basin

We analyzed the sequence stratigraphic framework,internal sedimentary characteristics and its controlling factors in Wunan sub-depression based on sequence stratigraphy principle.There are three third-order sequences in Wunan sub-depression during rift period.Each sequence is integrated in the sag and is denudated partially in Wudong ramp region,and the distribution range is controlled by faulted slope-break belt.Hydrocarbon source rock consists of high system tract and half deep lake facies in depressed stage.Main reservoir consists of the sand body of fan delta front and braided stream delta front which is present in high system tract or low system tract in lower part of Nantun Formation.The enriching belts of structural-lithological reservoir in Wanan sub-depression are due to the effective matching between source rock and reservoir.Hydrocarbon distribution shows zonation.The middle slope break is a main enrichment zone,and lower part of Nantun Formation is the main oil concentration area,which is a primary exploration area.