The Structural Evolution And Oil And Gas Distribution Of Urxun-Beier Depression In Hailer Basin

The Urxun and Beier depressions are two main oil-gas bearing depressions in the Beier lake depression zone of Hailar basin. In Late Jurassic and Early Cretaceous, Urxun-Beier depressions went through thermal uplift extensional rift period of Tamulan ditch Fm and Tongbomiao Fm, the extending rift period of Nantun Fm, the fault sag transformation period of Damoguaihe Fm, the weak extending rift period of Yimin Fm and the depression period in Late Cretaceous.Affected by the intra-continental subduction and mantle delamination in Tamulan ditch-Tobongmiao period, mantle in the deeper part of basin melted and developed into volcano-rock platform. Consequently, the extensional rift system failed to take shape and volcanic lava, pyroclastic rock, coarse clastic formation and small amount of fine clastic were found. Formation of Nantun period basin is mainly controlled by strike NE-NEE low angle extensional rift system and presents small-scale haft-graben fault depression and river-lake facies filling. During the period, the haft-graben fault depression was separated by strike NE-NEE ancient block salient. Damoguaihe period basin was a extensional rift and developed large-scale delta foreset characteristics with large range Sedimentary. By contrast, Yimin stage basin controlled by strike NNE-NE high angle fault system was a weak extensional rift fault system and developed swamp facies sediment. In the late Yimin stage inversion structure was formed when the superimposed basin subjected to compressional inversion.The filling and evolution of sediment basin was primarily controlled by the structural evolution of the basin and various semimetal filling characteristics were found in different tectonic evolution stages. Fault depression controlled by controlling-falling fault and fault convex configurations determined the characteristics of channel-valley controlling source and fault ramp controlling sand. Formation of the chief source rock series was mainly controlled by the NE-NEE extensional regime in Nantun Fm and the occurrence state of source rock was decided by NNE weak extensional process. The superimposition of Nantun Fm residual fault depression and Damoguaihe Fm fault sag, together with weak extensional fault depression in Yimin Fm, controlled the distribution of effective source rock in Nantun Fm.Structural action and sediment evolution controlled the collocation relationship of bear-reservoir-seal combination and oil-gas enrichment localization, forming Upper, middle and lower three sets of optimum reservoir-seal combination with major oil and gas occurrence in the central and lower part. Structural style determines the distribution of the oil and gas reservoirs in the basin.The main trap types are fault block and fault nose which developed through multi-phase overlay of extensional process in Nantun FM, weak extensional process in Yimin FM and folding in late Yimin FM. At the same time, there is stratigraphic reservoir and combined reservoir. We propose in this paper the uplift zone in depression and gentle slope fracture structural zone adjacent to source kitchen as hydrocarbon enrichment zone and make a prediction of 10 favorable exploration area with 4 areas for class I, 2 for II and 4 for III.