Abstract: The sedimentary characteristics and diagenesis of the Dongying Formation in the Bohai C oilfield are complex, and the physical properties change greatly. Evidence for oil and gas is common. Because are a large number of high-resistivity water layers as shown in logging data, it is difficult to identify the fluid types. The comprehensive analyses of well-logging results, core, rock and mineral data reveal that the high content of clay minerals, dominantly kaolinite, and high residual oil saturation are the two main factors for the high resistivity water layers. Based on the analysis of the genesis, we propose that the fluid replacement method and the intersection of deep resistivity and density curves can be used to quickly identify high-resistivity water layers. The application of the methods with measurement data shows that the difference between normalized deep resistivity and density is a sensitive parameter for identifying oil and water layer, according to the crossplot of ΔRd -Δρ vs. Rd, the oil layer mainly occurs
in regions where ΔRd -Δρ is greater than 2.3. This method could guide comprehensive evaluation of well logging in C oilfield and
even in the medium-deep reservoirs of Bohai area.

Key words: Dongying Formation, high-resistivity water layers, kaolinite, cenetic analysis, identification method