Abstract: Complex electrical well logging has been widely used in many oilfields. It is a powerful method for the low-resistivity, water-flooded and residual oil zone. However, frequency dispersion and incorrecte calculation of the real and image part of complex resistivity are the main reasons that restrict its development. The principle of complex resistivity logging are studied in this paper, and it is found that permittivity of the rocks and formation fluids have more distinguished response than resistivity of them. The previous experiments have been proved that the permittivity decreased with the distance square between two poles. Based on the results of the experiments, the new equations to calculate the saturation and salinity of formation water have been established, in addition, a circute that used to detect capacitivity is designed. The new method has been shown available for identifing the fluid by the oilfield data.

Key words: Complex resistivity, dispersion, logging, permittivity, fluid identification, dual-band dual laterolog