Tomographic Characterization of Residual NAPL in Porous Media Systems

We present in this paper a pore-scale characterization of residual NAPL in sand systems from high-resolution three-dimensional images at different experimental conditions. Synchrotron microtomography was used to obtain three-dimensional images of sand systems with different characteristics of grains and initial saturation of the wetting phase. Pore-scale characteristics of residual NAPL blobs including volumes, lengths, interfacial areas and shape descriptors were computed using three-dimensional image processing algorithms. Silica and quartz sands of different geometry and size distributions of grains were used to represent the porous media. Residual NAPL in each sand system was obtained following cycles of drainage and imbibition of water and NAPL. Initial wetting saturations in sand systems ranged from partial to complete saturation conditions. Five different fractionally wet sand systems comprised of 100%, 75%, 50%, 25% and 0% hydrophobic mass fraction were imaged and analyzed. Findings indicate that geometry and spatial variation in wettability of sand particles have a significant impact on pore-scale characteristics of residual NAPL in porous media systems.