The Sichuan Basin is a composite oil-and gas-bearing basin characterized bay Paleozoic marine deposits and Mesozoic-Cenozoic lacustrine deposits. Following the Late Triassic, the basin transitioned into an inland continental sedimentation stage, resulting in the development of lacustrine strata. The Upper Triassic Xujiahe Formation is the primary target for lacustrine gas reservoirs in the western Sichuan low-relief area, while the Da’anzhai Member of the Lower Jurassic Ziliujing Formation serves as the main target for lacustrine oilfields in the central Sichuan gentle slope area. This chapter focuses on the Da’anzhai Member, specifically in the Langzhong to southern Sichuan region, as a case study. It examines the depositional environment, biogeographic zoning, stratigraphy, sedimentary facies, primary source rock characteristics, and petroleum accumulation conditions. These insights provide valuable guidance for the exploration and development of lacustrine petroleum resources in the Sichuan Basin.