Linking continuum-scale state of wetting to pore-scale contact angles in porous media

Abstract Hypothesis Wetting phenomena play a key role in flows through porous media. Relative permeability and capillary pressure-saturation functions show a high sensitivity to wettability, which has different definitions at the continuum- and pore-scale. We hypothesize that the wetting state of a porous medium can be described in terms of topological arguments that constrain the morphological state of immiscible fluids, which provides a direct link between the continuum-scale metrics of wettability and pore-scale contact angles. Experiments We perform primary drainage and imbibition experiments on Bentheimer sandstone using air and brine. Topological properties, such as fluid morphology, distribution and interfacial curvature are measured utilizing X-ray micro-computed tomography at irreducible air saturation. We present measurements for United States Bureau of Mines (USBM) index, capillary pressure and pore-scale contact angles. Additional studies are performed using two-phase Lattice Boltzmann simulations to test a wider range of wetting conditions. Findings We demonstrate that contact angle distributions for a porous multiphase system can be predicted within a few percent differences of directly measured pore-scale contact angles using the presented method. This provides a general framework on how continuum-scale data can be used to describe the geometrical state of fluids within porous media.