- a. You are evaluating a sand where the porosity, m, and Rw remain constant. The lower part of the sand is water-bearing (Sw=100%) and has a resistivity of 1 m. The upper part of the sand has a resistivity of 7.4 2. m. If n=1.75, what is the water saturation in the upper part of the sand? b. If n can vary from 1.6 to 2.2, what is the possible range of water saturation in the upper part of the sand?