Modelling and Simulation of the Entrapment of Non-Wetting Fluids Within Disordered Porous Materials

The phenomenon known as non-wetting phase (nwp) entrapment, and the multiphase fluid flow within porous media that gives rise to it, is important in several areas such as contaminant transport and subsequent remediation, subsurface energy storage, oil recovery, carbon dioxide sequestration, and pore structural characterisation. The aim of this review was to survey the various different modelling and simulation approaches used to predict the pore-scale processes involved in the entrapment of nwp in disordered porous media, and the impact of pore structural features on the level of entrapment. The various modelling and simulation approaches considered included empirical models, pore network models (PNMs), percolation models, models derived directly from imaging data, and thermodynamic and statistical mechanical techniques. Dynamic flow simulations within models derived from images have validated the quasi-static idealisation for low capillary number, often used with PNMs. Modelling using this approximation has demonstrated the importance of pore connectivity and macroscopic heterogeneities in the spatial distribution of pore sizes in determining entrapment. Dynamic simulations in image-derived models have also shown the need for proper representation of menisci configurations in the complex void spaces of mixed-wetting systems in order to accurately predict entrapment, something that is not always currently possible.