Abstract: One of the key techniques for logging evaluation of water-flooded reservoir is to determine the resistivity of the mixed liquid of water-flooded reservoir. At present, the method of calculating the resistivity of the mixed liquid of water-flooded reservoir needs to be improved. In this paper,a dimensional dynamic material balance method is proposed to accurately calculate the resistivity of formation mixed fluid. The method makes the water flooding process microelement and takes into account the variable exchange ratio of original water and the injected water ions in the water flooding process. In theory, the variable gradually changes from 0 to 1 with the increase of flooding degree. The comparison results show that the average relative errors of the rock resistivity calculated by the first derivative method, the variable magnification material balance method, and the improved micro-element dynamic material balance method are 0.192, 0.169, and 0.124 respectively. The improved micro-element dynamic material balance method is more accurate when measuring the mixed solution resistivity in different flooding types. The residual oil saturation can be calculated more accurately in well evaluation. The method has been applied to the well logging evaluation of different flooding types in major oil fields. The calculated water saturation of water-flooded reservoir is the closest to the saturation data of the closed coring. The comprehensive interpretation coincidence rate of the flooded reservoir logging reaches more than 87%.

Key words: water flooded reservoir, water flooding dynamic model, mixed liquid resistivity, micro-element dynamic conduction mechanism