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 N-2/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 N-2/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 similar to 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 N-2/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.