Pore-scale modeling of mass transfer from nonaqueous phase liquids

A pore-scale model is developed to simulate mass transfer between two fluid phases in a porous medium. The model uses a network description of the pore space, and couples to a capillary displacement model, which explicitly tracks each fluid-fluid interface in the porous medium. Given explicit locations of all fluid-fluid interfaces, the mass-transfer model computes mass fluxes across each interface, then solves transport equations in the pore network to determine aqueous-phase concentrations. A stagnant-layer diffusion model is used for mass transfer, so calculated concentrations control the subsequent rates of mass transfer. The model is used to predict a dissolution front developed by flushing water through a column that is initially at residual NAPL saturation. Model results compare well to measured experimental results.