Investigation of the residual–funicular nonwetting-phase-saturation relation

• Published in: Advances in water resources 2000-11, Vol.24 (2), p.157-177
• Main Authors: Hilpert, Markus, McBride, John F, Miller, Cass T
• Format: Article
• Language: English
• Subjects: Capillarity; Hysteresis; NAPL; Network model; Residual; Snap-off; X-ray attenuation
• ISSN: 0309-1708; 1872-9657
• DOI: 10.1016/S0309-1708(00)00035-X

The constitutive relation that describes the amount of nonwetting fluid phase entrapment is critical to the modeling of multiphase flow in porous media, but it has received insufficient attention in the literature. We studied this relation using both experimental and modeling approaches: we used a nondestructive, X-ray monitored, long-column experiment that yielded a rich data set for two different porous media; we also used a quasi-static network model to simulate the experimental data and examine mechanisms affecting the relation. The experimental work yielded a significant data set for residual nonwetting phase (NWP) saturation as a function of maximum funicular nonwetting phase saturation. We suggest a functional form that represents the observed data sets accurately. Network model calibration to experimental data yields acceptable model-data agreement and a clear understanding of constraints that should be satisfied when using such models to avoid physically unrealistic behavior. We found that the pore-throat-size characteristics and the snap-off process occurring in pore throats strongly influence the manifestation of pore-body-size characteristics during imbibition and nonwetting fluid phase entrapment. We examined an estimation method proposed by Wardlaw and Taylor for the residual–funicular relation. We observed that the method yields an unrealistic relation for each porous media in the long-column experiments, and we used network modeling to understand the criteria that ensure a realistic estimate.