A steady-state kinetic interface-sensitive tracer (KIS-SST) method to measure capillary associated interfacial area...

We propose a novel method to measure the specific capillary-associated interfacial area (a_wn) between non-wetting and wetting fluids by applying kinetic interface-sensitive (KIS) tracers under steady-state two-phase co-flow conditions. Seven column experiments were conducted with a column filled with glass beads (diameter d₅₀ = 170 μm), serving as the solid grain network of a porous granular material. The experiments were performed for two flow scenarios, i.e., five experiments were performed for drainage conditions (increasing non-wetting saturation) and two experiments for imbibition conditions (increasing wetting saturation). To obtain different saturation levels in the column and, consequently, different capillarity-induced interfacial areas between the fluids, the experiments were performed for different fractional flow ratios (i.e., the ratio between injection rate of the wetting phase and total injection rate). The concentrations of the KIS tracer reaction by-product were recorded at each saturation level and the corresponding interfacial area was calculated. As a result of the fractional flow condition a wide range of wetting phase saturation is created (0.3 < S_w < 0.8). The measured a_wn increases with decreasing wetting phase saturation for the range 0.55 < S_w < 0.8, and then is followed by a drop in wetting phase saturation of 0.3 < S_w < 0.55. A good fit for our calculated a_wn is obtained (RMSE <0.16) using a polynomial model. Additionally, the results of the proposed method are compared to published experimental data and the method's main advantages and limitations are discussed.