Pore-scale modeling of extended two-phase flow and mass transfer in porous media

Computational pore-scale network models describe two-phase porous media flow systems by resolving individual interfaces at the pore scale, and tracking these interfaces through the pore network. Coupled with volume averaging techniques, these models can reproduce relationships between measured variables like capillary pressure, saturation, and relative permeability. These models additionally allow nontraditional porous media variables to be quantified, such as interfacial areas and common line lengths. In this work, relationships are computed between capillary pressure, saturation, interfacial areas, and common line lengths. This thesis further considers a conjecture that a three-parameter constitutive relationship between capillary pressure, saturation, and interfacial area may eliminate hysteresis between drainage and imbibition; for the investigated pore network sample, hysteresis is essentially eliminated with a physically plausible choice of model displacement rules.; An algorithm is developed to simulate mass transfer between two fluid phases in a porous medium. The approach builds on the pore-scale description and explicit tracking of the fluid-fluid interfaces in the porous medium. Mass transfer is computed as local mass fluxes across each interface and transport equations are solved in the pore network by a characteristic method. The concept of stagnant-layer diffusion is used to describe the interface mass transfer, where calculated local concentrations control the rates of mass transfer. The model results predict dissolution fronts developed in column experiments of porous media initially at residual nonaqueous phase saturation. The definition of macroscopic mass transfer coefficients is investigated and comparisons are made for rigorously up-scaled quantities.; Incorporation of nonaqueous phase dissolution allows new constitutive relationships to be determined over the full range of saturations, including residual phase saturations. To accommodate all saturations in a consistent way, capillary pressure is defined as the areal average of local capillary pressures associated with each fluid-fluid interface. Inter-phase mass transfer and miscible transport are modeled to generate the extended constitutive relationships. Dependencies of these extensions are presented with respect to system parameters. These new relationships indicate that special care is needed in the general formulation of continuum-scale equations for two-phase flow.