A method for estimating a relationship between physical properties of a porous material from a sample thereof includes making a three dimensional tomographic image of the sample of the material. The image is segmented into pixels each representing pore space or rock grains. The image is divided into sub-volumes. A porosity is estimated for each sub-volume. At least one petrophysical parameter is modeled from the image of each sub-volume. A relationship between the porosity and the at least one modeled petrophysical parameter is determined by, e.g., a best-fit statistical method. The relationship and the modeled petrophysical parameter for each sub-volume are stored in a computer or displayed.