Pore-scale modeling of electrical and fluid transport in Berea sandstone

The purpose of this paper is to test how well numerical calculations can predict transport properties of porous permeable rock, given its 3D digital microtomography (mu CT) image. For this study, a Berea 500 sandstone sample is used, whose mu CT images have been obtained with resolution of 2.8 mu m. Porosity, electrical conductivity, permeability, and surface area are calculated from the mu CT image and compared with laboratory-measured values. For transport properties (electrical conductivity, permeability), a finite-difference scheme is adopted. The calculated and measured properties compare quite well. Electrical transport in Berea 500 sandstone is complicated by the presence of surface conduction in the electric double layer at the grain-electrolyte boundary. A three-phase conductivity model is proposed to compute surface conduction on the rock mu CT image. Effects of image resolution and computation sample size on the accuracy of numerical predictions are also investigated. Reducing resolution (i.e., increasing the voxel dimensions) decreases the calculated values of electrical conductivity and hydraulic permeability. Increasing computation sample volume gives a better match between laboratory measurements and numerical results. Large sample provides a better representation of the rock.