The Pickett plot is a graphical solution used to help define water saturation parameters. A clean (low shale volume) water bearing interval should be used. A line drawn slightly below the southwesterly data represents the Sw=1.00 line. The intercept of the Sw=1.00 line at PHI=1.00 is equal to tortuosity exponent (a) multiplied by water resistivity (Rw) at reservoir temperature. Slope of the water saturation lines equals cementation exponent (m) multiplied by negative one. Saturation exponent (n) sets the distance between the water saturation lines.
Start by inputting resistivity-porosity 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 water saturation parameters (yellow cells with Rw, a, m and n inputs) until the water saturation lines fit the desired data series. Finally, customize the input values for the five constant water saturation lines which will be plotted (yellow cells with Sw value inputs).
GR Pickett "A Review of Current Techniques for Determination of Water Saturation from Logs," paper SPE 1446, presented at the SPE Rocky Mountain Regional Meeting, Denver, Colorado, USA, May 23-24, 1966; SPE Journal of Petroleum Technology (November 1966): 1425-1435.