Quantification of the velocity acceleration factor for colloidal transport in porous media using NMR

Nuclear magnetic resonance (NMR) techniques were used to quantify the transport of colloids through porous media. This was achieved via the application of chemically-resolved pulsed field gradient (PFG) methods, hence probing the displacement (probability distribution) propagators of both the colloidal and continuous liquid phase. A dilute decane-in-water emulsion was used with flow through a random glass sphere packing being considered. The acquired propagators allowed for quantification of both colloidal entrapment and the velocities of both the continuous phase and the flowing colloids. The flowing colloids were found to experience a velocity acceleration factor (VAF) increase of 1.08 relative to the continuous phase. This was found to be independent of displacement observation time or flowrate. It was speculated to be a consequence of radial exclusion due to the finite size of the colloids. Simulations of the colloidal transport were also performed using a lattice Boltzmann platform and a Lagrangian particle-tracking algorithm which incorporated colloidal radial exclusion. Reasonable agreement was observed between the simulation and the experimental data.