Anomalous Dispersion in Pore-Scale Simulations of Two-Phase Flow

We investigate anomalous dispersion in steady-state two-phase flow though a random, artificial porous domain. A natural distribution of trapped wetting-phase fluid was obtained via two-phase lattice Boltzmann drainage simulations. To avoid spurious velocities, accurate inter-pore velocity fields were derived via additional one-phase lattice Boltzmann simulations incorporating slip boundary conditions imposed at various interfaces. The nature of the active dispersion at various timescales was subsequently studied via random walk particle tracking. For our system, results show persistent anomalous dispersion that depends strongly on the assumed molecular diffusivity and the initial positions of tracer particles. Imposing slip versus no-slip boundary conditions on fluid-fluid interfaces made no observable difference to results, indicating that observed anomalous dispersion resulted primarily from the complex flow network induced by the trapped fluid phase.