Representative Elementary Volume Determination for Permeability and Porosity Using Numerical Three-Dimensional Experiments in Microtomography Data

Abstract

Combining tomographical reconstructed volumes and direct pore-scale flow simulations has proven to be an efficient tool in modern soil sciences. The main objective of the present paper is to present an extensive study about the usage of micro–computed tomography to obtain transport properties of porous media. The transport properties are obtained by means of pore-scale simulations whose domains are the pore space of the tomographical images of three different materials: glass spheres, sand, and clay. The main discussion in the present paper regards the definition of the representative elementary volume (REV). To address this issue, statistical analyses were carried out, showing that the REV concept is scale-dependent. Also, some guidelines considering the specification of the numerical domain size are discussed. It is shown that, for the glass spheres and sand, the coefficient of variation (CV) of the permeability decreases as the simulation domain increases, reaching values as low as 2%. In contrast, for clay samples, the CV does not show a clear decreasing tendency, and its values are approximately 75% for the largest domain size considered. Hypothesis tests were used to show that more than one domain size can be considered a REV (i.e., there are different minimum domain sizes for which permeability and porosity can be evaluated), and these values can be used to predict the transport properties of a larger part of the domain at a given scale.