Tectonic Characteristic And Petroleum Accumulation Of Yitong Basin

This dissertation mainly discussed tectonic characters, tectonic setting and tectonic evolution of Yitong graben, and analyzed the relationship between tectonic activities and oil-gas accumulation.Yitong graben is a strike-slip basin developed in Paleogene. The strike-slip basin underwent compression and extension: several generations of early Eocene extension (Shuangyang formation-fist segment of Yongji formation), extension and differential subsidence metaphase in late Eocene- late Oligocene(second segment of Yongji formation-Qijia formation) and end up under development compression in Neogene(Chaluhe formation).Boundary fault in northwestern margin of Yitong graben is quite different from that in southwesterm margin. The northwest boundary fault was a strike-slip fault, which was a sinistral strike-slip fault in early Eocene(Shuangyang formation-first segment of Yongji formation) but gave way to a dextral strike-slip fault in late Eocene-late Oligocene(second segment of Yongji formation-Qijia formation).In Neogene,it was reverse fault under regional compession(Chahelu formation),which controlled graben evolution to a great extent. The southwestern boundary fault was an extensional fault, which served as an accommonditing fault during graben evolution. No.2 fault was a branching normal fault of northwest boundary fault and southwest boundary fault, which separates the Moliqing-Luxiang and Chaluhe fault.The tectonic styles in the depressions can be divided geometrically into nine kinds:"stepped fault blocks","fault terrace(normal and antithetic)","graben","horst","imbricate structures","flower structures","Y"style structures","feather structures"and"anticline hinge subsidence".They could be grouped into two namely tectonic tectonic kinematics styles:"extensional faulted blocks"and"inversion structures".Unconformity surface of bedrock( paleo-weathered crust)was one of oil-gas transeverse migration pathways. Faults can be one of oil-gas vertical migration pathways besides as bars. Faulted block structure, fault-nose and fault anticline were main structures good for oil-gas accumulation. Fault- lithology compound structure, stepped fault- lithology compound, fault- lithology in the hanging-wall of Marginal fault and concealed hill structures were secondary structures for oil-gas accumulation.Based on the tectonic analysis on Yitong graben together with other petroleum geology conditions in key evaluation regions, Wuxing tectonic zone, Liangjia tectonic zone and Wanchang peri-clinal tectonic zone were proposed to be fault tectonic zones benefit to oil-gas accumulation.