The Formation And Evolution Of Hashan Structural Belt And Its Controlling On Hydrocarbon In The Northern Of Junggar Basin

The Hashan structural belt,which belonged to the northern part of overthrust belt in northwestern margin of Junggar Basin,located at the basin-range junction zone of Junggar Basin and Hala'alat mountain,is holding abundance petroleum resources and forming a multi-layers three-dimensional hydrocarbon reservoirs.However,there are some questions that restrict the next optimum-seeking of main exploration target,such as the complicated geologic structure,different hydrocarbon accumulation degrees between various structural zones,the unknown major controlling factors and regulation of hydrocarbon accumulation.In order to adapt the high quality and efficient exploration requirement,reduce the exploration risks and costs,it's needed to study the formation and evolution of Hashan structural belt and its control of hydrocarbon accumulation,to find out the hydrocarbon enrichment regulation,in the hope of providing guidance on the hydrocarbon exploration in Hashan area.Hashan structural belt which showed thrust-napped,thrust-overlapped,strike slip reworked early-failed piedmont zone,is a large thrust nappe structure.It can be divided into four geological structure units including the overlap-denudation zone,the allochthonous nappe system,the front thrust belt and the thrust superimposed belt and six periods of thrust nappe,controlled by the stress field transformation,stress effects patterns and the filling strata properties,its present structural features show vertical stratification,north-south subzone and east-west subsection.It's divided into two structural layers in profile which are shallow sloping zone and median-deep nappe thrust zone,and three structural deformation belts in plane which are reworked strike slip tectonic zone in the north,nappe superimposed-imbricate thrust tectonic zone in the central,and the low angle overthrust-thrust tectonic zone in the south.It develops overlying multi-stage thrust nappe of the Lower Permian and the Carboniferous in western segment,and overlying imbricate thrust of Triassic and Permian in eastern segment.Guided by the theories of fault-related folding and complicated structural analysis,this paper studied the geometry,kinematics and dynamics of the structure by using the data of regional tectonic,outcrop,drilling and seismic.It's divided into ivestages of tectonic movements,by the analysis of unconformity styles,fault cutting relations and the angle of axial planes of the structures.By analyzing the strata involved in the tectonic deformation and development characteristics of the growth-strata,the formation time of the structure is defined when the process and deformation of tectonic is defined by balanced cross-section restoring.On this basis,the structural and sedimentary evolution of Hashan structural belt since the late Paleozoic is rebuilt,which could be divided to six phases: early Permian slip extension phase,late of the Early Permian brittle ductile shearing-imbricate thrust phase,Late Permian para-foreland basin intensive nappe thrust-adjusted strikeslip phase,Triassic intracontinental basin inherited nappe thrust-resformed strike slip phase,Jurassic and Cretaceous intracontinental basin vibrated uplift phase and Cenozoic foreland basin and Himalayan strike slip phase.The key tectonic deformation phases are the late of the Early Permian,Late Permian and LateTriassic,which controled the original orogeny,strengthened uplift and defined shape of the Hala'alat mountain.The spatial-temporal collocation of hydrocarbon accumulation elements are controlled by the formation and evolution of Hashan structural belt and the tectonic deformation of the key phases,which result in the accumulation rules,distribution characteristics and properties of hydrocarbon from different structural units have their own characteristics.It's thought that the expanding-rifted structural setting and soda-lake sedimentary environment created condition for the development of high quality source rocks and clastic dolomitic volcanicmulti type reservoirs of the Fengcheng Formation in the Early Permian,when Hashan area was semi-deep lake face determined by structure restored.And as a result,resource rock is developed broadly,which is distributed in several blocks controlled by nappe-thrust of Hashan.The hydrocarbon generation evolution of resource rock was controlled by overlapping structural and compensating sedimentary stratigraphic,which include steadly burial drocarbon generating type,rapid uplift hydrocarbon stagnation type,quickly burial hydrocarbon generating type and secondary hydrocarbon generating type,the distribution of effective hydrocarbon source rocks from different building blocks was determined.The tectonic control functions on reservoir are shown in two aspects.One is the fault micro-fracture improving the physical properties of brittle volcanic dolomitic reservoir,the other is the tectonic uplift-erosion weathering having corrosion-transformed function on reservoir.And forming four types of reservoir including weathering type,weathering-fault transformation type,inner lithofacies-structure transformation type,matrix porosity structure transformation type.The formation and evolution of Hashan structural belt controlled the tectonic styles,sedimentary strata filled characteristics,the spatial-temporal collocation of hydrocarbon migration elements,as well as the time-space ordering of hydrocarbon migration and distribution regularity of different structural zones.By analyzing the geology and geochemistry conditions,it's figured out that there are two hydrocarbon migration systems: the “fault-carpet” distal lateral transportation model of overlap-denudation zone,and the “multi-fault”proximal vertical transportation model of nappe-thrust zone,of which the hydrocarbon migration system can be classified into three patterns: fault micro-fracture net-shaped migration system in the western nappe super imposed area,fault-sandstone stair-step migration system in the middle thrust super imposed area,and the migration system of fault first sandstone second in the eastern fault fold deformation area.The work together with tectonic evolution,hydrocarbon generation evolution of source rocks and the conducting style evolution control the dynamic evolution of hydrocarbon charging and accumulation.There are three times of hydrocarbon charging in the middle and the west which were at relatively early stages,while in the east,there were twice of hydrocarbon charging which were relatively late period.The factors of source rocks,conduit systems and reservoirs controlled the reservoir types and the hydrocarbon enrichment region in different tectonic units.Also,the preserve condition controlled the difference of hydrocarbon reservoir characteristics.It finally formed the multi-layer oil-bearing pattern in which light and heavy oil coexisted,different maturing stages hydrocarbon accreted.