Abstract: The exploration and development of biogenic reef oil and gas reservoirs in the margin zones on both sides of the Kaijiang–Liangping trough in the Sichuan Basin have achieved great success, but research on the bioclastic beach beneath the biogenic reefs remains limited. The reef beach reservoir is deep, with a small thickness, and it changes rapidly in both longitudinal and transverse directions, making it difficult to accurately predict the reservoir and develop benefits. In order to solve the above problems, reef beach reservoirs of Changxing Formation in Yuanba West District were studied. Based on the fine division of strata and the study of palaeogeomorphology, it was concluded that the sedimentary model of the reef beach reservoirs of Changxing Formation was formed in the early stage of Changxing Formation, and the biogenic reef was inherited and developed in the middle and late stages of Changxing Formation, thus forming the unique sedimentary characteristics of “upper reef and lower beach” in the longitudinal direction. Based on a deep understanding of the sedimentary model of the reef beach reservoir, a method for identifying the reef beach reservoir by combining well seismic analysis was proposed, successfully guiding the drilling of Well Y203H_C in the study area and achieving significant progress in the evaluation of reef beach development. The research results indicate that: ① The early stage of the Changxing Formation in the Yuanba West District exhibits a distal steep carbonate gentle slope sedimentary model, and the reef beach reservoir is mainly developed along the steep zone. ② The application of mixed phase deconvolution and F-X denoising techniques has improved the quality of seismic data, and waveform indication inversion has been used to enhance the accuracy of longitudinal reservoir prediction. Combined with GR waveform indication simulation technology, it effectively avoids carbonaceous mudstone traps and achieves quantitative prediction of thin reef beach reservoirs. ③ The research results have successfully guided the deployment of the first reef beach development evaluation well, and the drilling results have confirmed the reliability of the geological understanding and reservoir prediction mentioned above. It is concluded that the sedimentary model and prediction method of thin reef beach reservoirs are helpful for the exploration and development of reef beach reservoirs in the Sichuan Basin.