Tomographic measurement of interfacial area during imbibition in fractionally-wet porous media

Interfacial area between non-wetting and wetting phases is an important variable critical to understand and model many flow and transport processes in porous systems containing multiphase and chemical components. The objective of this research was to investigate the functional relationship between capillary pressure, wetting phase saturation, and interfacial area between wetting and non-wetting phases in fractionally wet porous media during imbibition. Synchrotron-based computed tomography was used to obtain high-resolution, three-dimensional images that capture changes in interfacial area during imbibition in sand systems that mimic natural subsurface environments. Imbibition experiments were performed in fractionally-wet sand systems (comprised of 100%, 75%, 50% and 25% hydrophobic mass fraction). To eliminate hysteresis effects, imbibition in each system started from the end point of the drainage process at which the wetting phase was irreducible. Interfacial area was computed from tomography images using robust and accurate image processing algorithms. Relationships among pressure, saturation and interfacial area (total interfacial area and meniscus area between non-wetting and wetting phases) will be presented and discussed in the context of fractional wettability of porous media.