There are low-gamma ray mudstones present in V oil zone of Bi 125 block, and the natural gamma ray of effective reservoirs has a wide range which crosses with that of ineffective reservoirs; the reservoirs are shallow, the salinity of formation water is low, the amplitude anomaly of self-potential is minor and the self-potential of effective reservoirs also has a wide range and its range crosses with that of invalid reservoirs. These two curves of identifying lithology are both or partially invalid, which makes it difficult to identify the effective reservoirs in the area. According to the fact that there is no low limit of logging curves to determine effective reservoirs of the objective intervals, the geological factors causing the complex phenomenon have been studied, and together with the actual data, integrated with the useful information contained in a variety of logging data, then, the models appropriate for the area have been established, including models of natural gamma amplitude anomaly marginal limits, self-potential amplitude anomaly marginal limits and invalid reservoirs removal. The application of these models makes the logging interpretation of effective reservoirs in the area possible and turns the adverse situation that the identification of effective reservoirs could only depend on coring and borehole log. With the application of the newly-established marginal reservoir identification model, 108 wells in the area have been reinterpreted, and 37 oil layers, up to 26.4 m thick, have been added; moreover, the misinterpreted 18 oil layers, 15.6 m thick, have been removed; and the thickness of numerous pre-interpreted oil layers has been corrected. The established identification models of complex-lithology effective reservoirs are suitable for the fast-deposited fan deltaic system and are expected to be applied to other fast-deposited systems such as alluvial fan and subsea apron.