This crossplot is based on Schlumberger's K4 chart and is used to determine permeability from porosity and water saturation. An interval above the transition zone should be used (no water production). The following equation is employed to draw the permeability lines:
A medium-gravity oil is assumed. If the saturating hydrocarbon does not meet this condition, a correction factor will need to be applied (see Raymer).
The blue lines represent equal bulk volume water and the red lines represent equal permeabilities. Lines are labelled with values.
The permeability equation can be rearranged to solve for water saturation, when porosity and permeablility are known. This enables estimation of water saturation from any rotary sidewall or routine core analysis (see Deakin). Solving for Swi, the equation becomes:
Start by inputting saturation-porosity data series, (green, blue and orange cells). Each data series allows for an unlimited number of rows of data, and cut and paste functionality is available. Once data have been loaded, record the predicted permeability range for each series.
Coates, G.R., and Dumanoir, J.R., "A new Approach to Improved Log-Derived Permeability." The Log Analyst January - February 1974.
Deakin, M., "How To Do Quick-Look Shaly Sand Log Analysis With Confidence." SPWLA Asia-Pacific Regional Conference, March 1-4, 2020.
Morris, R. L., and Biggs, W. P., “Using Log-Derived Values Of Water Saturation And Porosity.” SPWLA Eighth Annual Logging Symposium, June 12-14, 1967.
Raymer, L.L., "Elevation and Hydrocarbon Density Correction for Log-Derived Permeability Relationships." The Log Analyst May - June 1981.
Schlumberger's Industry Publication, "Log Interpretation Charts." K-4 Chart from 2000 Edition.
Timur, A., "An Investigation of Permeability, Porosity and Residual Water Saturation Relationships for Sandstone Reservoirs." The Log Analyst July - August 1968.