PORE-SCALE MODELING OF NONWETTING-PHASE RESIDUAL IN POROUS-MEDIA

The complexity of the formation and removal of nonwetting-phase residual in porous media provides a significant challenge to the development of theories needed to advance more effective aquifer remediation schemes. Constitutive theories are required to overcome theoretical deficiencies in describing behaviors such as the formation, dissolution, and mobilization of residual. Current macroscopic approaches are often unable to capture adequately the complexity of such processes, in these cases, pore-scale research should provide the necessary conceptual and quantitative basis for constitutive theory development. This work contributes to these efforts by investigating factors affecting residual in strongly wet, capillary-dominated systems. Porous media are modeled as three-dimensional networks of pore bodies and throats. A random network approach is developed, which provides stochastic geometry and variable connectivity. Immiscible displacement occurs via piston-displacement and film-flow mechanisms. Residual ganglia become trapped during imbibition. Wetting-phase continuity is maintained during drainage, disallowing the entrapment of wetting-phase ganglia. Results show that pore-scale geometric parameters significantly affect residual saturation, the ganglia-volume distribution, and nonwetting-wetting-phase interfacial area. Thus constitutive theory of residual should incorporate pore-scale knowledge to be valid for a wide range of conditions and porous media types. Comparison with quantitative experimental ganglia-volume distributions yields good agreement with the data trends but poor quantitative agreement. These results indicate the need for further experimental comparisons with theoretical results, linking macroscale and microscale theory and experiment.