Abstract: To study the lithofacies types and reservoir characteristics of gas-bearing shale in the Upper Permian Dalong Formation in western Hubei area, the drilling cores of Endi 2 Well were taken as the research object and analyzed by whole rock X-ray diffraction, organic carbon content, vitrinite reflectance, kerogen microscopy, field emission scanning electron microscopy, carbon dioxide and nitrogen physical adsorption experiments, shale gas content and trace elements. The results show that the main lithofacies types of the Permian Dalong Formation in western Hubei include siliceous rocks, clayey siliceous rocks and mixed siliceous rocks, and the clayey siliceous lithofacies has the highest average organic carbon content. The shale of Dalong Formation has multiple pore types. Micropores and mesopores contribute to the main pore volume and specific surface area of shale. High organic carbon and clay mineral content are conducive to the accumulation of shale gas and the establishment of micro-pore system (pore size < 50 nm) in shale, and the adsorbed gas in micropores and mesopores is an important part of the total gas content. This paper established the evaluation criteria of Permian Dalong Formation shale in western Hubei based on gas content and TOC. The results show that clayey siliceous lithofacies and mixed siliceous lithofacies are Ⅱ1 class advantageous lithofacies types, siliceous lithofacies are Ⅱ2 class advantageous lithofacies types, and the 1 241.0-1 250.4 m section of Endi 2 Well is the “sweet section” of shale gas. The relationship between trace elements and organic carbon content of shale shows that the high organic matter content of Dalong Formation is the joint result of high productivity and water reduction environment, and the high ancient productivity is the main reason for the enrichment of organic matter.

Key words: western Hubei area, Dalong Formation, shale lithofacies, pore structure, gas-bearing property, reservoir