Abstract: In view of the unclear understanding of the reservoir characteristics and main controlling factors of the Permian Changxing Formation in the platform-depression margin in eastern Sichuan Basin, this paper discusses the reservoir characteristics of the reef beach and the controlling effect of the reef beach sedimentation and diagenesis transformation on the Changxing Formation reservoir by using the methods of thin section identification, core observation and conventional physical property analysis. The results show that the reservoir rock types of the reef beach reservoir in the study area are bioclastic dolomite and reef dolomite. The main reservoir space types of bioclastic dolomite are intercrystalline pores, intercrystalline dissolved pores and non-fabric selective dissolved pores (vugs), while that of the reef dolomite consists of organic lattice pores and non-fabric selective dissolved pores (vugs). The reservoir physical properties are generally characterized by low-medium porosity and low permeability. The controlling factors of the reservoir include the material basis in the sedimentary stage and the dolomitization transformation in the syndiagenetic stage. In the sedimentary stage, along the high-energy zone in the platform-depression margin, belt-like discontinuous reef beaches were formed, which provided a material basis for dolomitization transformation in the later period. The medium-salinity seawater formed in syndiagenetic stage carries out dolomitization transformation on reef beaches along the primary pore spaces of reef beaches that have not been completely cemented by calcite of the first and second stages, which is the key factor for the formation of reef beach dolomite reservoir. The research results can provide strong support for the exploration expansion of reef beach gas reservoir in the Changxing Formation of eastern Sichuan Basin.

Key words: platform-depression margin, reef beach reservoir, reservoir characteristics, controlling factor, Changxing Formation, eastern Sichuan Basin