PNNL

Abstract

The study of non-aqueous phase liquid (NAPL) transport in groundwater requires a correct description of multiphase flow in porous media. For the simulation of multiphase flow a number of material-dependent parameters have to be known. These include relationships between capillary pressure, relative permeability, and saturation. One of the major difficulties in characterising a porous medium is the presence of small-scale heterogeneities, which have distinctly different multiphase flow properties than the main medium. Such heterogeneities can considerably affect the spreading behaviour of non-aqueous liquids. They are often sources of localised pools of pollutants. For most practical purposes, the details of fluid distribution in such a medium are not of interest. It is also computationally not feasible to discretise a compositional multiphase model at such small scales. Even if a detailed numerical model is constructed, it is virtually impossible to obtain data for these heterogeneities. Thus, instead of modelling the subsurface at the scale of micro-heterogeneities, it is desirable to model it at a higher scale, as a homogenised medium, with effective properties.