This crossplot is used to graphically determine a saturation exponent (n) value for a set of core data representing a particular rock type.
Resistivity index (I) is measured in the lab and is equal to the ratio of the true resistivity of the rock (Rt) to the resistivity of 100% brine saturated rock (Ro). Resistivity index (I=Rt/Ro) can also be determined with the equation I=1/Sw^n, where the slope equals saturation exponent (n).
Start by inputting Sw-I data series, (green, blue and orange cells). Each data series allows an unlimited number of rows, and cut and paste functionality is available. Next, adjust the saturation exponent value until the line fits the desired data series.
Archie, G. E., “The Electrical Resistivity Log As An Aid In Determining Some Reservoir Characteristics.” Transactions of the AIME Volume 146, Issue 1, December 1942: 54-62.