NAPL-Water Interfacial Area Estimation Using Kinetic Interface Sensitive Tracers in Porous Media: Modelling and Laboratory Experiments

Fluid-fluid interfacial area (IFA) in a two-phase flow in porous media is an important parameter for understanding the mass- and energy-transfer processes between the fluid-phases. New theories of multiphase flow in porous media suggest including the fluid-fluid IFA. A new category of reactive tracers has been proposed by Schaffer et al. (2013), termed kinetically interface sensitive (KIS) which are able to quantify the size of the fluid-fluid IFA. Previous experiments conducted by Tatomir et al. (2018) have demonstrated the application of the KIS tracers in a highly-controlled column experiment filled with a well-characterized porous medium consisting of an ideal well-sorted, highly spherical glass beads.

The aim of this work is to expand the applicability of the KIS tracer to other porous media systems and investigate the implications for the current continuum-scale numerical models. The first category of porous media is represented by glass beads, while the second category by natural quartz sand. In both categories two mean diameters are tested, a medium sand and a coarse sand. All four porous media have different diameter ranges, with different distributions and different uniformity coefficients. By applying KIS tracer method we provide a quantitative characterization of the impact of porous medium texture and grain surface texture and size on the NAPL/water IFA. Literature has shown from experimental and geometric models that the magnitude of maximum IFA is inversely proportional to the grain size of the porous media increasing linearly with decreasing grain diameters. The results obtained by the KIS tracer method reveal the same behavior. Moreover, obtained IFA values are consistent with literature data obtained with other techniques. The results show that KIS method can be added to the available laboratory methods to determining the fluid-fluid IFA, e.g. interface partitioning tracer tests, high-resolution microtomography. Furthermore, we investigate using a two-phase reactive transport pore-scale model which IFA the KIS tracer method is measuring (e.g., moving interface, film-associated interface, stagnant region).