A logging tool provides a log of fractional flow characteristics of formations surrounding an earth borehole. The logging tool is suspended in the borehole and resistivity measurements are made at different radial depths of investigation while the logging tool is moved through the borehole to obtain several resistivity logs. Model fractional flow parameters are selected, and a formation conductivity model as a function of the model fractional flow parameters is determined. Several simulated resistivity log values are generated at respective radial depths of investigation from the formation conductivity model. The simulated resistivity log values are compared with values from the resistivity logs of the resistivity measurements to obtain an error indication. The model fractional flow parameters is modified accordingly. Steps are repeated until a predetermined criterion is met, then an output of formation fractional flow characteristics is produced.