Accurately calculating the salinity and resistivity of mixed solution in water-flooded layers is the key basis for evaluating the water-flooded condition and remaining oil saturation in middle-late development stage. This paper focuses on simulating water-flooding processes with varying salinities and measuring resistivity at the rock core scale. A novel model for calculating the resistivity of mixed solutions was developed

taking into account the efficiency of injected-water sweep and ion exchange. This model was formulated based on theoretical analysis and provides an accurate representation of the properties of reservoir mixed solutions during water-flooding. It significantly enhances the accuracy of mixed-water resistivity calculations. The established model was successfully used in H Block of Qinghai Oilfield and the calculated water saturation was consistent well with the core analysis result with the total coincidence rate reached 92.33 %. The interpreted water-flooded layers were matched well with the actual production performance

the effectiveness of the established model was validated and lays a foundation for quantitative evaluation in the water-flooded layers.