The development of pore-scale network models for the simulation of capillary pressure - saturation - interfacial area - relative permeability relationships in multi-fluid porous media

The network modeling work presented in this thesis starts from the perspective that the defining property of multi-fluid porous media is the existence of interfaces separating phases, rather than the presence of multiple phases. Phase interfaces play a fundamental role in the flow of immiscible fluids and regulate interfacial mass-transfer between system phases. Of particular interest is the interfacial area separating wetting fluid from nonwetting fluid since these interfaces can change their shape in response to changes in capillary pressure. Despite their fundamental importance, phase interfaces are not explicitly incorporated in macroscopic formulations of multiphase flow and contaminant transport. Recent theoretical work of H. Majid Hassanizadeh and W. G. Gray has raised the question of whether capillary pressure should be viewed as a function of interfacial area, in addition to its traditional dependence on saturation. The two network models presented here provide a means of bridging spatial scales between pore-scale displacement processes and these macroscopic variables.; The first model uses a regular lattice of spherical pores connected by biconical capillaries. Its geometric simplicity was chosen to facilitate the calculation of meniscus geometries, and to explore the impact of immiscible displacement mechanisms on the capillary pressure-saturation relationship. A set of fluid-displacement-mechanism formulations yielding the most physically realistic behavior is determined. Interfacial areas are computed and comparisons are made between model results and hypotheses proposed by H. Majid Hassanizadeh and W. G. Gray and several proposed empirical relationships.; The second model uses a random pack of monodisperse spheres to define the pore space, and a representative pore network is extracted via spatial tessellation. Fluid displacement is simulated by modeling the stability and geometry of fluid-fluid menisci. This includes an explicit representation of pendular wetting fluid residing at grain-to-grain contacts. The simulated capillary pressure-saturation relationships are compared with physically derived data from glass-bead packs in order to assess the fluid displacement formulation stemming from the sensitivity analysis performed with the biconical model. Interfacial areas are computed in conjunction with capillary pressure and saturation, and these are compared with other researchers' predictions.