The two-phase flow IPTT method for measurement of nonwetting-wetting liquid interfacial areas at higher nonwetting saturations in natural porous media

Interfacial areas between nonwetting-wetting (NW-W) liquids in natural porous media were measured using a modified version of the interfacial partitioning tracer test (IPTT) method that employed simultaneous two-phase flow conditions, which allowed measurement at NW saturations higher than trapped residual saturation. Measurements were conducted over a range of saturations for a well-sorted quartz sand under three wetting scenarios of primary drainage (PD), secondary imbibition (SI), and secondary drainage (SD). Limited sets of experiments were also conducted for a model glass-bead medium and for a soil. The measured interfacial areas were compared to interfacial areas measured using the standard IPTT method for liquid-liquid systems, which employs residual NW saturations. In addition, the theoretical maximum interfacial areas estimated from the measured data are compared to specific solid surface areas measured with the N₂/BET method and estimated based on geometrical calculations for smooth spheres. Interfacial areas increase linearly with decreasing W-phase (water) saturation over the range of saturations employed. The maximum interfacial areas determined for the glass beads, which have no surface roughness, are 32 ± 4 and 36 ± 5 cm⁻¹ for PD and SI cycles, respectively. The values are similar to the geometric specific solid surface area (31 ± 2 cm⁻¹) and the N₂/BET solid surface area (28 ± 2 cm⁻¹). The maximum interfacial areas are 274 ± 38, 235 ± 27, and 581 ± 160 cm⁻¹ for the sand for PD, SI, and SD cycles, respectively, and ∼7625 cm⁻¹ for the soil for PD and SI. The maximum interfacial areas for the sand and soil are significantly larger than the estimated smooth-sphere specific solid surface areas (107 ± 8 cm⁻¹ and 152 ± 8 cm⁻¹, respectively), but much smaller than the N₂/BET solid surface area (1387 ± 92 cm⁻¹ and 55224 cm⁻¹, respectively). The NW-W interfacial areas measured with the two-phase flow method compare well to values measured using the standard IPTT method.