Pore-scale analysis of permeability reduction resulting from colloid deposition

High-energy, synchrotron-based x-ray difference microtomography (XDMT) was combined with lattice Boltzmann simulations to assess changes in pore-scale flow patterns and bulk permeability resulting from colloid deposition in a granular porous medium. The detailed structural information obtained from XDMT was used to define internal boundary conditions for simulations of pore fluid flow both with and without colloidal deposits. As colloids accumulated in the pore space, the mean tortuosity increased and the tortuosity distribution became multi-modal, indicating the development of macro-scale heterogeneity. These structural changes also produced large reductions in bulk permeability that were not captured by empirical or semi-empirical estimators based on the first-order geometric properties of the porous medium. This work demonstrates that coupling between fluid flow and particle transport produces heterogeneities at the sub-millimeter scale that greatly affect the hydrogeologic properties of natural porous media.