Sedimentary Environments and the Stratigraphic base-level Cycle Division of Jurassic Coal Measures in the East of Junggar Basin

The eastern Junggar basin located on the northeastern edge of the large down warped lake basin in Jurassic.Mainly three sets of thick coal layers developed in the east of Junggar basin Jurassic strata,respectively lying at the bottom of Xishanyao group,the upper part and the lower of the middle part of Badaowan group.The coal layer of Xishanyao group and the upper part of Badaowan group were formed in the stage of lacustrine regression delta and they are thick and stable regionally.The coal layer of the lower of the middle part of Badaowan group was formed shore swamp in the stage of lacustrine transgression and it is thin and stability in region.The coal accumulation environment and stacking pattern are controled by base-level and accommodation in the eastern Junggar basin.The accommodation is affected by the structural uplift and basement differential subsidence in the eastern Junggar basin in Jurassic.Accommodation move toward the center of the basin in the process of lacustrine regression and there are bulky accommodation below shoreland where peat are preserved advantageously in the upper section of Badaowan group and the bottom of Xishanyao group.The two sets of coal layers may be acted as the transfer surface of sedimentation.The coal layer of the down of the middle part of Badaowan group may be regard as first flood surface of lacustrine and sequence boundary.Based on accurate correlation of the high-resolution sequence stratigraphy,distribution regularity of oil,gas and water of Xishanyao group reservoir can be explained reasonably in the Well CAI 31 area.It has obtained a good effect on the identification of subtle reservoir and precise reservoir description.