A push-pull kinetic interface-sensitive tracer method to quantify the fluid-fluid interfacial area in dynamic two-phase flow in porous media

The kinetic interface-sensitive (KIS) tracer, relying on a zero-order reaction on the fluid-fluid interface, is a newly developed method to measure the fluid-fluid interfacial area (FIFA) in drainage processes. The concentration of the reaction product, obtained by measuring the water samples after the breakthrough, is interpolated with numerical model to determine the FIFA. However, a major limitation of the previous method is that the volume of available water sample is highly dependent on the sand type and the system parameters, and the measurement is not applicable when the water sample is not sufficient. An alternative is to apply the KIS tracer in the “push-pull” test, meaning the drainage process is followed by an imbibition process with the flow direction reversed. This study applies the pore-scale numerical simulation and the column experiment to study the KIS tracer reactive transport during a push-pull test. The breakthrough curve of the product concentration is interpolated with both macro-scale numerical model and a modified analytical solution for the push-pull process. It is found the shapes of the concentration breakthrough curves from the pore-scale simulations and the column experiments are fit, showing a non-linear descending trend with respect to time. The KIS tracer reactive transport process in the push-pull test and the validation of the measured FIFA from the concentration breakthrough curve, are demonstrated based on the pore-scale simulation results. Finally, for the (n-octane/water) displacement process in the column packed with the glass beads with diameter of 240 μm (at the capillary number of 5×10^-7), the FIFA is measured 210 m^-1 at the water saturation of 0.33, which is consistent with some literature data.