“In the development of marine shale gas in southern China, traditional lithofacies classification has shortcomings. Experts have proposed a reservoir facies classification method based on thermal evolution degree, organic matter content, and mineral composition. Through thin section observation, scanning electron microscopy (SEM), and various experimental tests, a systematic analysis of the reservoir facies characteristics of the Lower Silurian Longmaxi Formation shale in the southern Sichuan Basin has been conducted. A reservoir facies index grading standard has been established, and over mature organic rich siliceous shale has been determined as the optimal reservoir facies, providing new ideas for improving the accuracy of reservoir evaluation.”