An Experimental Study of Capillary Pressure Hysteresis in Two-phase Flow in 2D Porous Micromodels

Two-phase immiscible flow in porous media occurs in many environmental and industrial systems. Traditional models often describe these flows based on empirical constitutive relations (e.g., capillary pressure vs. saturation) which exhibit hysteresis. It has been the goal for many recent studies to develop a nonhysteretic relation of capillary pressure to link pore to macro-scale through thermodynamically constrained averaging theory (TCAT) and geometric measures. However, experiments are still needed to validate and further develop the theories. To that end, we present a pore-scale measurement of capillary pressure, saturation, interfacial area, curvature, and Euler characteristic employing 2D microfluidic devices called micromodels and high-speed fluorescent microscopy. The uniqueness of the capillary pressure-saturation relation under different flow histories is investigated. We further discuss the geometric theorems applicable to two-phase constitutive relation and how the inclusion of new variables in the model reduces hysteresis under quasi-static and transient conditions. These results will provide new insight into the hysteretic behavior of capillary pressure as well as validations of new functional forms.