The Late Reconstruction Process Of Bayanhot Basin And Its Petroleum Geological Significance

The Bayanhot Basin is located in the southeastern edge of Alax Block,which is a composite-superimposed basin formed by different periods and many tectonic movements.Predecessors have conducted some research on the sedimentary geological conditions in the Bayanhot Basin,confirming that the carboniferous in this basin may have good hydrocarbon conditions.However,due to the complicated geological conditions and the strong later reformation in the basin,oil and gas exploration has failed to achieve a breakthrough.Therefore,whether from oil and gas exploration or scientific research,it is of great practical significance to carry out a comprehensive study on the structural changes and later reformation after the carboniferous in the study area.The Late Paleozoic sedimentary structures in the Bayanhot Basin are unclear,and the basin is strongly reconstructed in the late period and the distribution of the faults is unclear.In this study,the combination of field outcrops around the basin,intra-basin seismic data,and drilling coring methods was used to start from sedimentary construction and later reformation.This is an ancient comparison and mutual restraint.The reform of the basin is clearly defined and the dynamic evolution of the basin is restored,and then determine the geological significance of the later reformation of oil and gas.Comprehensive analysis of a large number of seismic data,combined with previous research results,a systematic summary of the fault characteristics,formation period and structural styles of the basin believed that:The strike of faults is mainly NE,NNE,NW-NNW and near-EW direction.The period of fault activity is mainly Carboniferous,Late Jurassic,Late Jurassic-Early Cretaceous and Cenozoic,some faults are inheriting and present the characteristic of multiperiodic activity.Because the Bayanhot basin has experienced multiple periods of compression uplift and extensional rift,this leads to the basin has developed a wide range of tectonic styles,such as extrusion,extension,strike slip and inversion.A total of nine structural styles were identified in the study area,which includes Graben-Horst combination,semi-graben,stepped fault combination,rift extension structure,vertical and horizontal anticline,cut off anticline,imbricate thrust fault combination,back thurst structure and opposite thrust structure.Based on the existing drilling and seismic data in the basin,the distribution of t he Carboniferous and its overlying strata in the study area and the comprehensive ana lysis of the unconformity surface are considered.It is considered that the Carbonifero us in the study area has been reformed by three tectonic movements in the late Herc ynian-Indosinian,Yanshan and Himalayan periods.The main types of reformation are squeezed fold deformation,uplift denudation,superimposed deep burial and thermodyn amic action.The late Hercynian-Indosinian tectonic reformation is the most intense res formation period in the entire basin,resulting in differential uplift and erosion of the Carboniferous.The main tectonic reformation in Yanshan period is to make the Carbo niferous strong thrust deformation,uplift and denudation and thermodynamic reformati on caused by magmatic activity.The later reformation of Carboniferous in the Bayanhot Basin has the characteristics which is stronger in the west than the east and stronger in the north than the south.And in the process of later reformation,the accumulation center of Bayanhot Basin has a law of clockwise migration from southeast to northwest,and then to the northeast,which reflects the different stages of structural reformation and basin sedimentary dynamics mechanism changes.The studies suggest that the Bayanhot basin has been subjected to a strong later reformation since the late Paleozoic deposition.Especially,the late Hercynian-Indosinian and Yanshan tectonic movements is obvious for the basin reformation,which makes the Carboniferous source rock distribute mainly in the long and narrow belt in the eastern and southern depression of the basin.The extensively developed magmatic activities in the Yanshan period also promoted the evolution of source rocks in the study area,and the uplifting and subsidence in different phases also had a great impact on the hydrocarbon accumulation in the later period.