Structural Features Of Chaiwopu Sag In Junggar Basin And Its Control Of Hydrocarbon Accumulation

The Chaiwopu Sag is a multi-stage superimposed basin developed on the Carboniferous fold basement,belonging to the southeastern edge of Junggar Basin.The Sag contains the Yilian Haber Mountain in the south with the Bogda Mountain in the north,present a basin-mountain mosaic pattern.It has the unique petroleum geological characteristics of the superimposed basin,and develops various sets of source rocks such as Permian and Jurassic,corresponding to multiple sets of reservoir-cap combination with good prospects for exploration.This paper studies the tectonic deformation characteristics and deformation periods of the Chaiwopu Sag since the Late Paleozoic,and analyzes the overall evolution process of the entire Sag,which is of great significance for understanding the formation of oil and gas geological conditions in the Chaiwopu Sag.Through our research,following understandings have been achieved:1.There are two series of thrust faults in the Chaiwopu Sag.Among them,the“north-east”fault developed extensively in the study area,mainly formed in the Indosinian period;the“near-east”fault developed mainly in the front of Yilian Haber Mountain and Dabancheng sub-sag,the former developed in the Hexi period,and the latter formed in the late Yanshan-Xishan period.2.The Chaiwopu Sag was absolutely thrust by the peripheral mountains.During the late Permian,it was mainly laterally squeezed by the southern margin of the Yilian Haber Mountain,developing basal involvement faults in the area.During the propagation of the fault,it developed a series of recoils faults and fault-related folds.At the end of Jurassic,affected by the uplifting orogeny of the Bogda Mountain,the Sag developed a series of southward thrust faults near the piedmont zone,and developed a hedge belt at the intersection between the south thrust faults and the north thrust faults.3.Based on the analysis of seismic interpretation and logging data,we conduct field geological surveys and identify three unconformity interfaces in the Chaiwopu Sag and it's adjacent areas.From bottom to up there are:Unconformity interface under Shangcangfanggou Group,unconformity interface under Badaowan Formation,and unconformity interface under Paleogene.4.Since the late Paleozoic,the Chaiwopu Sag has experienced multiple phases of movement such as Varisian movement,Yinzhi movement,Yanshan movement and Himalayan movement.Affected by these movements,the superimposed Sag experienced rift basin development stage(C₂-P₂),depression basin development stage(P₃-T),wide basin development stage and inter-mountain basin development stage(E-).5.Based on the study of the evolution of the Chaiwopu Sag,we studied the types of source rocks,reservoirs,caps and traps in the work area next.The results show there are multiple sets of source rocks,reservoirs and caps system,which have the conditions for multi-stage accumulation.In addition,the main trap types in the Sag are fault traps for it's developed faults,and there are few other types of traps,such as lithologic traps and Stratigraphic traps.