Tectonic Evolution And Accumulation History Simulation In The Northern Depression Of Wuwei Basin

The northern depression is located in the north of Wuwei Basin,which is located in the southeast of Hexi Corridor Basin Group,and at the intersection of three structural units:North China Block,Qilian Fold System and Helantai Fold Belt.However,there is no previous study on the relationship between tectonic evolution and accumulation process in different periods by using balanced profile technology and basin simulation technology,which restricts the further exploration and development of oil and gas resources in this area.In this paper,combined with logging,seismic and geochemical data sources,based on systematic analysis of stratigraphic lithology,paleo-water depth,paleo-heat flow value and other parameters in the study area,the structural evolution and reservoir-forming history of the study area are simulated by using balanced profile technology and reservoir-forming simulation technology.The results of tectonic evolution analysis show that the main tectonic evolution stages in the study area are as follows:(1)During the Hercynian rift development stage,due to the southward subduction of the ancient Asian Ocean,the Alashan block in the late Hercynian period was in the active continental margin arc environment,the southern Qilian basin subducted and disappeared under the continental crust and started orogenic activities,while the northern depression occurred rifting,and all levels of faults controlled the development of the "single fault" dustpan graben and "double fault" graben distributed in the northeast;(2)During the uplift and denudation stage of Indosinian period,due to the influence of Indosinian movement,the northern Qilian and Hexi Corridor areas rose as a whole,resulting in the overall lack of Triassic sediments in the study area;(3)In Yanshan fault block development stage,from early Jurassic to middle Jurassic,Longshoushan fault in the north was right-lateral strike-slip,with internal extension and tension,and the fault depression began to develop.The north-east part of the study area was the center of the fault depression,while the west part was in the uplift area.During the Late Jurassic,the Qilian Mountains in the north of Longshou Mountain in the study area experienced intense orogeny,and the compression uplift of the study area suffered denudation.In the early Cretaceous,affected by the collision between Gangdise block and Eurasia,Qilian Mountain region was uplifted,and the region was continuously affected by NE-SW compression and right-lateral strike-slip.The NE-trending fault extended again,and a series of NE-trending rifts expanded,and the sedimentary range expanded,and began to form a unified lake basin;(4)During the Himalayan depression formation stage,in Tertiary,influenced by the collision between Indian plate and Eurasian plate,the study area was once again in the right-lateral strike-slip structure background,which caused the NE-trending fault to extend right-lateral strike-slip again.During this period,the control of fault activity on sedimentation weakened and began to change to depression stage.In Quaternary,the southern part of the study area suffered from compression,uplift and denudation.During this period,the fault activity was extremely weak and the whole area was in depression stage.The simulation results of oil and gas accumulation show that the thermal evolution degree of source rocks in the northern depression of Wuwei basin is generally high,and it begins to enter the hydrocarbon generation threshold at the end of Carboniferous Since the end of Permian,Carboniferous source rocks have entered the mature stage;Since the end of Triassic,Carboniferous source rocks have entered a high maturity stage;At present,the Carboniferous source rocks in a high maturity stage.Combined with the comprehensive analysis of structural evolution stage and simulation results of reservoir forming history,the northern depression of Wuwei Basin can be used as a favorable area for oil and gas exploration.