There is a significant variation in the productivity of the same sedimentary microfacies in the median porosity—median to low permeability reservoirs of the Z layer in F oilfield in the South Caspian Basin. A comprehensive study was conducted on the types of diagenesis and reservoir characteristics of the Z layer by using casting thin sections, scanning electron microscopy, core mercury injection experiments, and logging data. According to the study of rock casting thin sections, scanning electron microscopy, and clay mineral analysis in this area, the main characteristics of diagenesis are as follows: mechanical compaction, secondary quartz enlargement, carbonate cementation, dissolution, as well as the characteristics of clay minerals and their impact on reservoirs. In this study, the authors established the logging facies characteristics of different types of reservoirs, determines quantitative discrimination criteria for different reservoirs. The reservoirs can be divided into four types based on diagenesis, diagenetic minerals, etc. The four types are as following: distributary channel facies, distributary mouth bar facies, overbank sand facies, and inter distributary facies. The selected logging curves such as natural gamma ray (GR), resistivity (RT), and spontaneous potential (SP), were used to establish logging identification standards for each reservoir facies, and to process logging data from all wells in the oilfield research area to obtain the distribution pattern of reservoir facies profiles. Based on the analysis of the matching results with the physical property analysis, it is believed that in the case of undeveloped fractures, the physical properties of the developed layers in the distributary channel are the best, followed by the distributary mouth bar facies, the overbank sand is the third one, and the subfacies inter distributaries is the worst, generally non reservoir.