Development Characteristics And Accumulation Conditions Of Deep Central Uplift Belt In Songliao Basin

Songliao basin that is an area of 260 thousand square kilometers is a Mesozoic large continental petroliferous basin in Northeast China.This paper makes a systematic study of deep central uplift belt in Songliao Basin by means of sedimentation,tectonics,geophysics and geochemical analysis.The Paleozoic in Songliao Basin underwent complex structural transformation,mainly related to plate movement.In the Precambrian period,the old blocks in Northeast China were separated from the Siberia plate and existed independently on the ancient Asian Ocean.In the Silurian period,Jiamusi and Songliao blocks collided and collaged.From the late Devonian to the Early Carboniferous Period,ancient blocks formed a unified Jiamusi Mongolia block in this way of collision and collage.From The middle Permian to the early Triassic period,Jiamusi Mongolia block and North China plate collided completely,and the ancient Asia Ocean was closed.From late Jurassic to early Cretaceous Period,The collision between the North China plate and the Siberia plate formed a unified Eurasian continent.Add to the Mesozoic period,strike slip between Pacific plate and Isa Nagi plate caused complex tectonic settings and varied lithological characteristics of Paleozoic in Songliao Basin.The deep central uplift belt in Songliao basin is located in the central part of Songliao basin,and was made up of some Paleozoic Secondary bulge.Having analysis from its framework,the central uplift was divided to two segments by Jalaid Banner to Jilin fault,Overall performs “North South high-low,North South old-new,North South wide-narrow”.The North segment is saddle type that the both end are higher than the Middle segment.The East-West central uplift is divided into zones by several eastward tensional fractures,showing zoning characteristics.The formation of central uplift is the result of differential settlement of both sides of fault.It is the relative bulge between a large scale fault depressions.The two sides of it is controlled by boundary fault.In Paleozoic,the central uplift belt was located in deep water sedimentary area,and the central uplift began to develop in the early Cretaceous Huoshiling formation of Mesozoic,and the major development period was the depositional period of the Shahezi formation.But up to the Yingcheng formation,the central uplift began to shrink,and fix absolutely in the depositional period of Denglouku(Quantou)formation.The formation time of central uplift was meantime with the fault depression,It was not a inherited paleo-uplift.The Permian especially the middle-late Permian is the major source rocks.In the well drilling,the content of organic carbon is more than 0.4,accounting for about 70% and more than 1,accounting for about 50%.In the field profile,the content of organic carbon is more than 0.4,accounting for about 90% and more than 1,accounting for about 20%.Generally,the Vitrinite reflectivity is less than 3%.The high Vitrinite reflectance value in some region comes to 6%,but the low is only 0.5%.According to chromatographic analysis of saturated hydrocarbons in source rocks,the Pr/Ph of the Permian source rocks is 0.3 to 0.67,It is less than 1,so It represents the Sedimentary environment of reductive water body.Apart to the Paleozoic source rocks,the Mesozoic source rock is also the major one.The migration pathways of oil and gas are unconformity,overlying sedimentary interfaces and faults.The type of reservoir is interior reservoir and weathering crust reservoir that mainly exist in High position of bulge.Drilling revealed the thickness of the weathering crust 4.4 to 72.61 m.The interior reservoir is mainly divided into three types: the partition between metamorphic rocks,the inner sedimentary rocks under the granite,and the internal depositional layers in different bands.From the characteristics of the development of the cover,the North of the central uplift is covered by mudstone of Denglouku formation,and the South is covered by Quantou formation,the thickness of mudstone is 20 to 99 m.As the central uplift developed to the fault depression,the cap rocks transform to Faulted strata.Combining the reservoir factors of central uplift with matching relation,we think of the Zhaozhou bulge,and Wangjiatun-Weixing-Shengping bulge which are closed to Xujiaweizi fault depression to be a favorable hydrocarbon migration and accumulation point.