In recent years, exploration and testing have shown that a set of carbonate reservoirs developed in the first member of the Middle Permian Maokou Formation in the Fuling area of the southeastern Sichuan Basin. These reservoirs have good gas-bearing properties and prospects for oil and gas exploration. The lithology of the reservoir is complex, with "eyeball" and "eyelid"-shaped structures commonly observed. The pore system shows strong heterogeneity with pores and fractures well developed. The reservoir spaces are mainly grain margin pores (fractures), diagenetic shrinkage pores (fractures), organic pores, and fractures. The porosity and permeability are separately distributed in ranges of 1%~5% and 0.01~1 mD, with the characteristics of ultra-low porosity and ultra-low permeability of the carbonate reservoir. The strong heterogeneity leads to the inaccurate effectiveness evaluation of the reservoir by conventional well-logs. Therefore, based on the analysis of reservoir characteristics, it is necessary to jointly combine the conventional well-logs, electrical imaging logging, core experiments, and gas testing to comprehensively evaluate the reservoir's effectiveness in three aspects of lithology, physical properties, and fractures. The research results show that: (1) Four kinds of lithology, namely stucco limestone, nodular stucco limestone, micrite limestone, and nodular micrite limestone, develop in the Mao-first member. The lithology of the gas-producing layers is mainly stucco limestone and nodular stucco limestone; (2) The physical properties of the reservoir are the stuccoed limestone and nodular stucco limestone, followed by micrite limestone and nodular micrite limestone; (3) The fractures mainly develops in the stucco limestone and nodular stucco limestone, with the largest fracture porosity and effectiveness.