Sensitivity of Pore-Scale Flow and Dispersion to Properties of Random Bead Packs

Comparisons between pore-scale simulations and physical experiments are complicated by the difficulty of reproducing the geometry of the experimental porous medium. For example, obtaining the coordinates of the beads in experimental bead packings is difficult, so pore-scale simulations typically develop geometry with some type of sphere-packing algorithm. Simulated and experimental geometries may have similar porosity but otherwise no direct correspondence. Flow and dispersion are affected by resulting differences in packing density, random packing variations, mild polydispersity, nonrandom packing defects, and confining walls. The authors will present recent results on the sensitivity of pore-scale simulations to these physical parameters and to certain simulation parameters. Simulation and experiment may also differ in methods for obtaining dispersion statistics. Dispersion coefficients are often inferred from experimental column breakthrough data, although more recently they have been inferred from changes in NMR signal intensity within the measurement section of a column. Simulation techniques based on particle tracking differ from breakthrough experiments but have some similarity to NMR measurement techniques. The present method for long-time simulations of dispersion will be presented and some issues in the experimental evaluation of asymptotic dispersion will be discussed. As time permits, results will also be presented on the sensitivity of flow and dispersion to the numerical treatment of no- slip boundaries, and a highly vectorizable implementation of the standard LBGK algorithm for viscous fluid flow.