The Structural Styles And Hydrocarbon Accumulation Of The Midwest Part On The Southern Margin Of Junggar Basin

The southern margin of the Junggar Basin is in front of the northern Tianshan Mountains,it is an oil and gas accumulation area of the typical polycyclic superimposed foreland basin in the west.Based on the field geological data and seismic data,under the guide of fault-related folding theory and tectonic control hydrocarbon theory,tectonic style and structural reservoir,evolution of traps and oil-trapping process have been studied detailly in this paper.Through the analysis of the main controlling factors of reservoir formation,the role of fault control is clarified,and the models of hydrocarbon accumulation in the central and western margins of the southern margin is summarized.The fault-related folds dominated by compression structures are mainly developed in the southern margin of the Junggar Basin.The structural style has the characteristics of upper and lower layers,and can be divided into two combinations of deep and shallow.The deep layer is detachment fold,and the decollement is located in the coal seam of the Jurassic Xishanyao Formation.The shallow layer is the fault-propagation fold,and the fault develops along the Paleogene Anjihaihe Formation mudstone.And two different shades of anticline are superimposed.The three rows of anticline exhibit different structural features: the first row of anticline is characterized by developmental basement thrust fracture and base-entangled structural wedge or tectonic wedge.The Jurassic strata are strongly pleated,forming a series of anticline structures,and the representative structure is Qigu anticline.The second row of anticline develops a slope anticline formed by fault-propagation fold,usually developed on the detachment fault.The most typical structure is the Huo-Ma-Tu structural belt.The third row of structural anticline structures with the development of detachment fold,such as the Hutubi anticline.The first row of anticline structures in the southern margin of the Junggar Basin was mainly formed in the Late Yanshanian movement at the end of the Jurassic,matching the peak period of hydrocarbon generation and expulsion of the Upper Permian and Middle and Lower Jurassic source rocks,and then undergoing a strong transformation of the Himalayan movement.Most of the Cenozoic strata have been denuded,and the anticline structure is mainly composed of the Jurassic and Triassic strata.Therefore,the accumulation model can be summarized as:self-source mixed source-near-source vertical transport-self-generated self-storage,ancient new deposit-multi-stage accumulation.The second and third rows of anticline tectonic belts are mainly formed in the second tectonic movement of the Himalayan from the late Pliocene to the early Pleistocene,which is beneficial to the Paleogene oil and gas accumulation,and has the fault to communicate with the deep Jurassic oil and gas sources.Therefore,the reservoir-forming model has the characteristics of dual-source hydrocarbon supply-near-source vertical transport-the paleozoic new reservoir-late accumulation.