Pore-Scale Characterization of Residual Non-Aqueous Phase Liquids (NAPLs) in Fractional Wettability Porous Media

The objective of this research was to investigate the impact of wettability of porous media on pore-scale characteristics of residual non-aqueous phase liquids (NAPLs). Synchrotron X-ray microtomography was used to obtain high-resolution 3D images of fractional wettability sand systems. Pore-scale characteristics of NAPL blobs such as volumes, lengths, interfacial areas and shape factors were computed from the 3D images. Four systems of different NAPL-wet mass fractions containing the residual NAPL were imaged and analyzed. In systems comprised of 100%, 50%, 25%, and 0% NAPL-wet mass fractions, residual NAPL saturations were 0.125, 0.067, 0.083, and 0.121; mean blob volumes normalized by the volume of a sphere with mean grain diameter were 0.97, 1.23, 1.93, and 2.39; normalized mean blob interfacial areas were 43.75, 35.86, 34.25, and 30.88 mm^–1; and mean sphericity index values were 0.216, 0.262, 0.455, and 0.569, respectively. Findings revealed that spatial variation in the wettability of porous media surfaces has a significant impact on pore-scale characteristics of residual NAPL blobs in saturated porous media systems.