Multi-scale simulations of waterflooding and surfactant flooding in microfluidic micromodels

Abstract

Recent experiments at the Colorado School of Mines focused on visualization of water-oil displacements in microfluidic channels to understand the underlying flow principle and to decipher the associated dynamics. In this PhD thesis, I conducted continuum-scale water-oil numerical simulations and modeled four microfluidic experiments. The four experiments included water-oil and surfactant-oil displacements in homogenous and vuggy heterogeneous geometries. I used a single-phase lattice Boltzmann method to determine absolute permeability of the microfluidic channels as input for several water-oil simulations. The ultimate purpose of my modeling was to determine how reliable conventional relative permeability equations are when they were varied to match the experimental data. I used, specifically a Modified-Brooks-Corey equation and the analytical solution for two-phase displacements in a single capillary tube. I systematically evaluated oil recovery factors, breakthrough times, and distributions of the invading and resident fluids. The results showed that experimental results can be matched by a Modified-Brooks-Corey relative permeability equation after their parameters are adjusted. The result of sensitivity analyses were applied to one of the microfluidic devices to evaluate the effects of capillary pressure on oil viscosity, was consistent with expected trends. While I achieved match between experiments and numerical models, the flow physics used in the continuum-scale numerical models needs further improvement. For instance, there is a need to better quantify relative permeability and capillary pressure functions for use in continuum-scale formulations. In this research, an original and interesting observation is that relative permeability curves, derived from the analytical solution of an oil-wet single capillary tube, intercept at a water saturation above 50%, which is usually associated with water-wet media. Thus, the Modified-Brooks-Corey relative permeability curves used in modeling were forced to retain this feature in order to obtain best match with experimental data. Other known criteria for the oil-wet media include (1) connate water saturation should be generally less than 15%, and (2) water relative permeability endpoint should be greater than 50%. In this thesis, I adhered to these criteria.