Novel fluid-fluid interface domains in geologic media

Pore-scale fluid processes in geological media are critical for numerous applications in several fields. Continued improvement of high-resolution image acquisition and processing methods has provided a means to directly characterize pore-scale fluid processes for natural geomedia, and to test the representativeness of theoretical and computational models developed to simulate them. High-resolution synchrotron X-ray microtomography (XMT) combined with advanced 3-D image visualization was used to investigate the impact of larger-scale solid-surface heterogeneity on nonwetting-wetting (air-water) interfacial area for two natural geomedia (a sand and a soil). The studies revealed the presence of air-water interfaces associated with water residing within macroscopic features such as pits and crevices on the surfaces of the solids. The diameters of the features ranged from tens to 100's of μm for the sand, and the aggregate associated air-water interfacial area was estimated to represent ∼12% of the maximum capillary interfacial area. These features and respective fluid interfaces, which are not considered in standard conceptualizations of fluid distribution in geomedia, may have an impact on pore-scale physical and biogeochemical processes.