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

摘要

The purpose of this paper is to test how well numerical cal-culations can predict transport properties of porous perme-able rock, given its 3D digital microtomography (μCT) im-age. For this study, a Berea 500 sandstone sample is used, whose ACT images have been obtained with resolution of 2.8 Am. Porosity, electrical conductivity, permeability, and surface area are calculated from the μCT image and com-pared with laboratory-measured values. For transport proper-ties (electrical conductivity, permeability), a finite-difference scheme is adopted. The calculated and measured properties compare quite well. Electrical transport in Berea 500 sand-stone 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 sur-faceconduction on the rock μCT image. Effects of image res-olution and computation sample size on the accuracy of nu-merical predictions are also investigated. Reducing resolu-tion (i.e., increasing the voxel dimensions) decreases the cal-culated values of electrical conductivity and hydraulic per-meability. Increasing computation sample volume gives a better match between laboratory measurements and numeri-cal results. Large sample provides a better representation of the rock.