Micro-CT Analysis to Explore Salt Precipitation Impact on Porous Media Permeability

Abstract

The concern for water scarcity as a future reality for a growing proportion of the planet is driving the need to understand in greater detail the role of water in ecosystem sustainability and resiliency. Pertinent to this conversation is the role that salt precipitation and salinization has on soil resources. This paper addresses this task by presenting results of a detailed study on the reduction in gas permeability of a porous media by subflorescent salt precipitation. Using high-resolution CT scanning and detailed Lattice Boltzman Modeling, the three dimensional distribution of salt was mapped and its effect on permeability was calculated. It was found that salt precipitate mass increases towards the soil surface and that the effect of subsurface precipitation on gas permeability was significant, potentially impacting gas exchange processes between atmosphere and vadose zone. In addition, results from the LBM were compared to estimates using the Koseny-Carman equation. A good correlation between these two methods indicates that the Koseny-Carman equation may be sufficient to calculate changes in permeability, providing a more accessible tool relative to the more complicated LBM approach. This study has made it clear that knowledge of the spatial distribution of salt precipitation is essential for any estimation of gas permeability changes due to subflorescence.