Abstract: Lithofacies identification and reservoir characteristics study of shale are fundamental to the geological evaluation of shale gas exploration and development.Based on the drilling data,X ray diffraction and thin section analysis,we proposed a scheme for lithofacies classification of marine shale.Then,we systematically analyzed the reservoir quality of varying shale lithofacies from the Wufeng Formation-Longmaxi Formation's first member,based on geochemical test results such as the total organic carbon(TOC) content,pore structure,porosity-permeability properties,lamina features,gas-charging properties,etc.The stratigraphic member developed three categories of shale lithofacies in the Fuling area,which can be subdivided into five major lithofacies(argillaceous-siliceous shale,dolomitic-argillaceous-siliceous shale,siliceous-clay shale,mixed argillaceous-siliceous shale,and mixed dolomitic-argillaceous-siliceous shale).There is a significant difference in reservoir characteristics between various lithofacies:the siliceous shale is a high-quality lithofacies with high TOC,high porosity and high gas content.The sedimentary setting determines reservoir quality development,while also controlling the shale lithofacies development.During the sedimentation of siliceous shale in the lower Wufeng Formation-Longmaxi Formation's first member, frequent volcanic activities provided abundant nutrients for plankton outburst,and induced an oxygen-poor and anaerobic environment which is conducive to the preservation of organic matter and the development of organic carbon-rich siliceous shale.The mixed shale and argillaceous shale developed in the middle and upper part of the first member are affected by bottom current and terrigenous debris supply respectively,which led to an oxygen-rich depositional environment,deteriorating the preservation condition of organic matters,thus lower content of TOC and less gas generation.

Key words: lithofacies, reservoir quality, shale, Longmaxi Formation, Fuling area, Sichuan Basin