Lithofacies types and reservoir differences of marine continental transitional shale in Linxing area，eastern margin of Ordos Basin

In order to explore the influence of transitional facies shale on the reservoir development characteristics，the transitional facies shale of Taiyuan Formation in Linxing area of Ordos Basin was taken as the research object，the shale facies types were divided by X⁃ray diffraction experiment and rock thin section observation sys⁃ tem. The reservoir characteristics of different lithofacies were analyzed in detail based on the test data of pore structure and gas content. The results show that according to the mineral composition，the Taiyuan Formation shale in the study area can be divided into four lithofacies types，namely clay type，siliceous type，mixed type and calcareous type. Fur⁃ thermore，it can be divided into high organic matter rich siliceous shale，medium organic matter rich siliceous shale，medium organic matter calcium siliceous shale with 2% and 4% organic carbon content as the boundary. The medium organic matter is rich in clay，siliceous shale and argillaceous / siliceous shale. Clay shale is in terrestrial fresh water and sub reduction environment， with relatively high organic carbon ( 4. 46%) content and gas content (1.44 m3 / t on average)，well⁃developed micropores，large pore volume and specific surface area，and good reservoir and adsorption capacity，but the brittleness index is the lowest，with an average of 33.5%. The mixed shale is deposited in saline water environment，with relatively low organic carbon content (1.65% on average)，poor devel⁃ opment of micropores and mesopores，the lowest gas content，and the brittleness index between clay shale and siliceous shale. Siliceous shale is in brackish water⁃salt water and sub⁃reductive environment，with average organic carbon con⁃ tent of 2. 07%， well⁃developed micropores and mesopores， low gas content， high brittleness index and easy fracturing. Generally speaking，the clay shale reservoir has a great hydrocarbon generation potential and development prospects，and can be evaluated on the basis of fully consideration on the brittleness index of the reservoir.