A new statistical approach to pore/throat size distribution of porous media using capillary pressure distribution concept

Abstract

This paper proposes a method of an indirect representation of pore/throat size distribution (PSD) of porous media using capillary pressure curves by introducing two important concepts; Capillary Pressure Distribution (CPD) and Pressure Duration.First, the drainage Pc- Sw trend was modeled using a Shifted Power equation involving three regression parameters. The CPD curves were then obtained using the capillary pressure curves for five desired Pressure Durations (Pressure Duration is defined as a specific pressure range (ΔPi) based on which the vertical axis (Pc axis) in capillary pressure curve is divided into equal ranges of capillary pressure). This duration can be of various sizes depending on the application.A diagram including five curves (for five durations) of distribution (or percent of drainage) vs. Pressure Duration were then plotted, each having a peak point, representing the average mean capillary pressure (Pcm.av) of the porous medium under study which is a measure of degree of homogeneity of the medium. Finally, it was shown that the CPD curve, indirectly, accounts for size distribution of the medium; hence, no need to calculate the PSD curve. Of course, simply, using CPD curve, the PSD curve as well as the average mean throat size (if drainage process) or pore size (if imbibition process) of the medium can be obtained using the general capillary pressure equation.