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Abstract

Liquid invasion into a porous medium is a phenomenon of great importance
in both nature and technology. Despite its enormous importance, there is
a surprisingly sparse understanding of the processes occurring on the scale
of individual pores and of how these processes determine the global invasion pattern. In particular, the exact influence of the wettability remains
unclear besides the limiting cases of very small or very large contact angles
of the invading fluid. Most quantitative pore-scale experiments and theoretical considerations have been conducted in effectively two-dimensional
(2D) micromodels and Hele–Shaw geometries. Although these pioneering
works helped to unravel some of the physical aspects of the displacement
processes, the relevance of 2D models has not always been appreciated for
natural porous media. With the availability of X-ray microtomography, 3D
imaging has become a standard for exploring pore-scale processes in porous
media. Applying advanced postprocessing routines and synchrotron microtomography, researchers can image even slow flow processes in real time and
extract relevant material parameters like the contact angle from the interfaces
in the pore space. These advances are expected to boost both theoretical and
experimental understanding of pore-scale processes in natural porous media.