Interfacial Areas and Immiscible Fluid Structures of Oil and Water in Oil-Wet and Water-Wet Porous Media

Abstract

ABSTRACT The objective of this study is to obtain quantitative evidence of pore-scale immiscible fluid distribution in oil-wet and water wet porous media using x-ray computed microtomography. Temporal and spatial saturation profiles, as well as surface and interfacial areas are thoroughly analyzed through cycles of drainage and imbibition using samples with different wetting characteristics but similar pore structures. Furthermore, the population of individual immiscible fluid structures (blobs') is also evaluated. The specific non-wetting phase surface areas of both porous media are found to be in close correlation with the specific solid surface area. On the other hand, the differing wetting strengths of the two porous media affects the fluid fluid interface, and thus the specific meniscus interfacial area of the two porous media. The specific meniscus interfacial area trends towards a maximum at wetting phase saturations of 0.35–0.55 for both porous media. The saturation of the maximum specific meniscus interfacial area is that of the greatest fluid-fluid interaction. The differences in wetting characteristics are also apparent in the blob populations. The number of blobs in the oil-wet porous media is three times greater than that of the water-wet porous media at similar saturations; the increase in population is due to the increase in the amount of smaller blobs being found in the more weakly-wetting oil-wet porous media, a result of lacking wetting-phase dominance in the smaller pore spaces. The surface areas of individual blobs as a function of the individual blob volumes are found to closely agree with that of a sphere at blob volumes below the minimum individual grain volume, and with the specific pore space surface area above this volume. These results show how the pore space geometry, wettability and saturation history influence the distribution of immiscible fluids within the pore space; these general observations can be a powerful resource for the improvement of multiphase fluid flow property prediction, properties such as relative permeability and capillary pressure.