Using a Fast X-Ray Microtomography Study to Better Inform Two-Phase Flow Theories

Understanding multiphase flow in porous media is important to many fields including groundwater management and remediation, soil and agricultural practices, petroleum engineering, and geologic sequestration of CO2. Scientists and engineers in these fields require experimental data acquired under field conditions to accurately create models of the dynamic multiphase flow processes being studied. The recent introduction of fast x-ray microtomography (fast-µCT) allows multiphase flow experiments to be performed in 3-dimensions under field-consistent pressure conditions removing the decision to either sacrifice the 3rd dimension with 2D micromodels or impose a pseudo-equilibrium pressure condition using standard-µCT methods. This new experimental method allows for the acquisition of data under more relevant conditions to validate multiphase theories with greater confidence and inform more accurate models. One such multiphase flow theory introduces interfacial area as a state variable that can be used to better describe the characteristics of two-phase flow by reducing or eliminating the hysteric effect that is prevalent in many two-phase models. Using fast-µCT, interfacial area production and evolution can unprecedentedly be tracked in 3D under valid flow conditions. Previously, we presented a preliminary analysis that suggested that the capillary pressure-saturation-interfacial area (Pc-Sw-Awn) surface established under flow conditions does not coincide with the surface obtained under pseudo-equilibrium conditions, which is complementary to work done in 2D micromodel studies. Here we present a more in-depth analysis on the relationship between Pc-Sw-Anw surfaces obtained under flow or pseudo-equilibrium conditions. In addition, we present an analysis of the measured interfacial area production rate term (Ewn) in relation to the rate of change of saturation (dS/dt) during the two-phase flow experiments which is an important relationship in two-phase theories.