Structural Characteristics And Its Influence On Hydrocarbon Accumulation In Eastern Qaidam Basin

On basis of drilling data,seismic data,gravity-magnetic-electric data,with referen-ce of predecessors' achievements,directed by theory on fault related fold,by means of quantitative analysis and qualitative analysis,combined with geology and geophysics,the author make deep research on structural characteristics and its evolution history of eastern Qaidam basin.Results indicated that there developed three thrust systems namely marginal thrust system,intrabasinal thrust system,intrabasinal strike-slip structure system and three kind of structural patterns such as compression,extension,and strike-slip.Tectonic stratigraphic framework of eastern Qaidam basin can be summarized as south-north division and east-west zoning.Structure evolutionary history during Mesozoic and Cenozoic can be subdivided into four phases,which are,weak stretching fault-compressive depression sedimentary stage during Early–Middle Yanshanian,intensive compressional depression–erosion sedimentary stage during Late Yanshanian,compressive depression sedimentary stage during Paleogene and Neogene,compressional strike-slip sedimentary stage during late Himalayan epoch,and Nappe–strike slip type structural evolutionary history is establish-ed.Based on the new insight into the tectonic evolution characteristics,the author concluded new idea as the following: sedimentation of Mesozoic was controlled by weak stretching rift–extruding during Early–middle Yanshanian;residual distribution of Jurassic strata in the study area were controlled by intensive compression and erosion during Late Yanshanian;source rock evolution,hydrocarbon generation,oil-gas accumulation and preservation were all controlled by intensive compression during Hymalayan movement.The prototype basin of Jurassic is recovered by a “seven step” method,which includes the definition of the basin property,clarification of formation thickness and distribution,determination stratum structure,recovery the denudation thickness and conformation distribution of original sedimentation.According to new idea,eastern Qaidam basin was divided by Mahai-Dahongou,Oulongbluk,and Chaidan rises into 4 separate lake basins namely Gaxi-Yuka,Hongshan-Xiaochaidan,Huobuxun and Deli-ngha.And this is essential to get clear understanding in relationship between present residual sag and prototype basin during Jurassic.Distribution regularity of Lower to Middle Jurassic and its controlling factors have been implemented by multiple methods.Meanwhile,geothermal evolution history of source rocks and the diversity in different basin styles are ascertained.New viewpo-ints are presented in hereafter,which can be explained as: continuous subsidence basins are sags with mature oil kitchen,and positive inversed basins are sags with low-mature source rock.Integrated relevant conclusions in aspects of structure,hydrocarbon-generation,evolution process of hydrocarbon-generation and its difference,the author established dynamic matching relationship among structure,hydrocarbongeneration and evolution process,and then point out that continuous subsidence basins are the most favorable exploration region,especially in those inherited structural belt closing to oil kitchen.