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

The constitutive relation that describes the amount of nonwetting fluid pha se entrapment is critical to the modeling of multiphase flow in porous medi a, but it has received insufficient attention in the literature. We studied this relation using both experimental and modeling approaches: we used a n ondestructive, X-ray monitored, long-column experiment that yielded a rich data set for two different porous media; we also used a quasi-static networ k model to simulate the experimental data and examine mechanisms affecting the relation. The experimental work yielded a significant data set for resi dual nonwetting phase (NWP) saturation as a function of maximum funicular n onwetting phase saturation. We suggest a functional form that represents th e observed data sets accurately. Network model calibration to experimental data yields acceptable model-data agreement and a clear understanding of co nstraints that should be satisfied when using such models to avoid physical ly 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 nonwe tting fluid phase entrapment. We examined an estimation method proposed by Wardlaw and Taylor for the residual-funicular relation. We observed that th e method yields an unrealistic relation for each porous media in the long-c olumn experiments, and we used network modeling to understand the criteria that ensure a realistic estimate. (C) 2000 Elsevier Science Ltd. All rights reserved.