Abstract: The volume of clay within clay-bearing formations is determined throughout the formations. This volume of clay is then functionally related to measurements indicative of formation porosity, such as density and neutron well logs of the formations. Utilizing measured formation characteristics representative of different clay types, such as potassium content or bound water content, the formation porosity measurements are extrapolated to indicate the porosity log measurements which would be yielded if the logging devices were responsive only to the clay within the formations. These extrapolated measurements are then related to known or determinable formation characteristics to determine additional formation properties such as porosity, permeability, and fluid saturation characteristics.