Abstract: In order to identify the relationship between the petrochemical composition and mineral properties and the gas-bearing property of the shale reservoirs in Weiyuan Structure in the low-steep fold belt in the southwestern Sichuan Basin. Core samples were taken from the lower Silurian Longmaxi Formation in the W202 Block of the Weiyuan Structure, and studied on rock chemical elements, shale mineral types and characteristics, organic carbon content and adsorption capacity. It was found in the study that the lithology of Long₁¹ Sub-member of Longmaxi Formation was mainly lime (dolomitic) shale, siliceous shale, carbonaceous shale, and clay shale; mineral type was dominated by terrigenous minerals, authigenic minerals, bioclasts and a little amount of organic matter; there were 4 layers in the vertical direction, but their petrochemical characteristics were obviously different; the Layer I of the Long₁¹ Sub-member was developed with quartz, with hight brittleness, rich pyrite, high organic matter abundance and strong adsorption capacity, and it was a quality reservoir for shale gas. This study provides a technical support for the adjustment of exploration and development plans for shale gas reservoirs.

Key words: shale gas, petrological characteristics, mineral composition, gas-bearing property, mechanical brittleness, Weiyuan Structure, Longmaxi Formation