The Tectonic Feature And Hydrocarbon Accumulation In The Northwest Part Of Junggar Basin

The relationship among structural deformation,structural styles and hydrocarbon accumulations in the northwest part of Junggar Basin is a hot issue on the study of tectonic geology and petroleum exploration in piedmont zone of Western China these years,especially in the area of Halaalate Mountain and its front deformation zones.According to the interpretation of seismic profile and analysis of subsidence history and thermal chronology, the tectonic sequence framework,fracture characteristics and structural deformation styles and the relationship between neighboring orogenic belt and them are analyzied.Also,the source rock,hydrocarbon accumulation period,hydrocarbon accumulation assemblage and favorable exploration areas are discussed.(1) According to the field geological survey and isotopic dating,the periods of volcanic rock in Xin1 well,Ying1 well and of the coal-bearing series in Upper Paleozoic are clear,as well as their stratigraphic horizons belonging.Also,the regional stratigraphic correlation and tectonic sequence framework are built.(2) With seismic profile interpretation,it is revealed that Halaalate mountain and its front deformation zones show basement-involved type asymmetric flower structure.And that belt can be divided into two parts,the strong deformation zones of basement-involved type on the north and the weak deformation areas of sedimentary covered on the south.The deformation may undergo thrust nappe during the early-middle Hercynian,and then come through compressional strike slip during the late Hercynian-Yanshanian.It has mainly been finalized during middle Yanshanian.(3) By the analysis of the subsidence history of wells and uplift history of the neighboring mountain,the differential uplift process between the northwest of Junggar Basin and the mountain are revealed.During C₂-P₁ the mountain rapid uplift and the basin rapid subside.During P₂-K₁ the mountain uplift slowly and the basin subside slowly.Since Cenozoic they both uplift. (4) Based on the source rock test,fluid inclusion temperature and illite dating,it shows that middle-upper Permian,Triassic and middle-lower Jurassic are the main effective source rock in northwest of Junggar Basin.There are several hydrocarbon source beds in Mahu drpression on south of the study area.Additionally,there are two main hydrocarbon generation and hydrocarbon accumulation periods in northwest of Junggar Basin:the middle-late Triassic and late Jurassic-early Cretaceous.Since late Cretaceous,hydrocarbon generation is slowing down even boging down,and the reservoir is reformed or destructed.(5) The analysis of allocation relation between tectonic and source rock in the study area presents that there are several sets of hydrocarbon accumulation assemblages in the front deformation zone of Halaalate Mountain:C₂-P₁,P_2-3,T_2-3,J_1-2 and K₁.The favorable exploration targets in mining rights range are H-1 and H-2 anticline traps below Carboniferous thrust nappe rock slices.