Network modeling of two-phase flow in porous media

A 3-D network model was developed and used to study pore scale processes in porous media and their effects on macroscopic capillary pressure-saturation relations and relative hydraulic conductivity for strongly wetted systems at low capillary number. It is a physically based model that includes capillary, gravity and entrapment of the nonwetting phase by bypass and snap-off mechanisms.; The influence of pore size distribution, pore tortuosity, aspect ratio, spatial correlation of pore size and gravity on the water retention curves and relative hydraulic conductivities for both wetting and nonwetting phase was studied. At different stages of drainage and imbibition, the occupation status of each pore and capillary tube and the flow paths for both wetting and nonwetting phases was determined. The macroscopic capillary pressure, saturation status and conductivity of the network were computed and compared.; The study showed that pore level modeling is an effective and powerful tool to understand the impact of microscopic properties on macroscopic constitutive relationships. Drainage processes are relatively simple to model and predict, while imbibition processes are much more complex and variable.; Entrapment of the nonwetting phase can occur by bypass mechanisms and/or snap-off mechanisms. The relative frequency of snap-off mechanisms and where they occurred were mainly determined by the aspect ratio of the network and the bond number of the system. It was found that the aspect ratio and the bond number played a major role in determining the water retention curves and relative hydraulic conductivities.; As the aspect ratio of the network decreases, entrapment of the nonwetting phase during imbibition decreases and, consequently, hysteresis decreases. As the bond number increases, the drainage and imbibition displacement fronts become flatter and more uniform. The water retention and relative hydraulic conductivity curves become scale dependent, questioning the Darcy approach which is based on the representative elementary volume concept where macroscopic properties are scale independent.