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.