Pore Scale Modeling of Rock Properties and Comparison to Laboratory Measurements

Abstract

The microstructure of a porous medium and the physical characteristics of the solid and fluid phases determine the macroscopic transport properties of the medium. The purpose of this paper is to test numerical calculations of the geometrical and transport properties (electrical conductivity, permeability, specific surface area, and surface conductivity) of porous, permeable rocks, given their 3D digital microtomography (μCT) images. We focus on μCT data for a 23.6% porosity sample of Berea Sandstone 500 (BS500) with 2.8 micron resolution. Finite difference methods are used to solve the Laplace and Stokes equations for electrical and hydraulic conductivities. We show that the permeability and formation factor are well correlated using a hydraulic radius computed from the digitized image. Electrical transport in the BS500 sample is complicated by the presence of clays. A three phase conductivity model, which includes the double layer length and counter-ion mobility, is developed to compute interface conductivity from the μCT image and measured values of the cation exchange capacity (CEC). Our calculations compare well with the laboratory measurements on cm[superscript 3] core samples. Finally, we examine the influence of image size and image resolution on our numerical results.