On Emergence of Phase Discontinuities in Porous Media.

Extensive works has been done to model and predict the flow and transport processes in a porous media both under saturated and unsaturated conditions. However, the current theories and models of multiphase flow in partially saturated media does not address well certain transport processes in soils such as the hysteric nature of water retention and unsaturated permeability, abrupt slow-down of evaporation from drying porous media and preferential and focused flow in seemingly homogenous porous media among others. In this work we argue that the limitation of the current theories lies in their implicit assumption of a continuous distribution of all phases throughout the portion of the porous media that is co-occupied by different phases. The hypothesis in this work is that fluids in partially saturated porous media can exist as disconnected islands and the emergence and/or existence of these phase discontinuities affects most of the macroscopic processes in a porous media. In this study we will conduct experiments that allows establishment of unsaturated flow under controlled boundary capillary potentials using a hanging column to demonstrate the existence of disconnected fluid islands in partially saturated media for two sand samples with coarse and fine sizes. The specific objectives of the experiment is to determine both the proportion of water that isolates completely when an initially saturated homogenous sample is subjected to varying rates of drainage and the amount of water needed to re-establish the lost connections during drainage. A Br-solution, which is non-reactive and non-volatile conservative tracer will be used in this experiment. We expect the results from this work to provide quantitative empirical confirmation on the occurrence of phase discontinuities and some of its main applications to fluid distribution.