Multiphase flow in porous media governs engineering applications at the center of two of the most pressing challenges facing humanity, energy access for an exponentially growing global population and climate change. In these systems, the wettability distribution is an extremely influential parameter in dictating the resulting microscopic displacement efficiency from a pore in addition to the potential capillary trapping, and typically undergoes spatial and temporal variations within a specific system. In this dissertation, direct numerical simulations of pore-scale multiphase flow in porous media using the lattice Boltzmann method are coupled with a wettability alteration algorithm to better capture mixed-wet states.

An investigation into the relative importance of the various factors contributing to a mixed-wet state including the wettability-altered fraction, the degree of wettability alteration, and the accurate contact angle assignment is performed. The interactions between the competing effects of wettability on flow enhancement, due to increased connectivity, and resistance, due to larger fluid-solid interfacial areas, become more complex as a function of the aforementioned factors and can result in larger flow resistance and more tortuous flow paths in fractionally wetting systems in comparison to a strongly wetting system. We observe that the wettability-altered fraction results in the strongest effects on the macroscale flow behavior, followed by the degree of alteration and contact angle assignment which increase in importance for larger wettability-altered fractions. A novel algorithm is developed to track spatial and temporal variations in the wettability state through monitoring the interactions between the fluid system and the domain. In addition to capturing the wettability-altered fraction and the relative degree of wettability alteration, the data generated from the algorithm can be utilized to design enhanced oil recovery operations and analyze capillary trapping potential, without requiring any simulation post-processing.

The necessity of capturing both wettability alteration and pore topology during direct numerical simulations is highlighted in two domains of varying heterogeneity by observing the resulting pore-scale displacement mechanisms, fractional flow effects, and phase trapping. The extent of remobilization and coalescence events due to wettability alteration is observed to be correlated with increased domain heterogeneity, larger capillary numbers, and comparable phase saturations. An additional complexity is observed in neutral-wet systems in that the local interface shape and the resulting displacement mechanism are controlled by the pore geometry which further stresses the importance of capturing wettability alteration as a function of the domain to accurately determine recovery and trapping potential. The applicability and efficiency of utilizing direct numerical simulations to monitor microscopic displacement efficiency and capillary trapping in a representative sample are illustrated. The effects of several enhanced oil recovery operations are analyzed through varying the relevant simulation parameters such as wettability, viscosity ratio, and interfacial tension. The rates of recovery enhancements are found to be correlated with the frequency of occurrence of the identified pore-scale displacement mechanisms, which are enhanced by the extent of wettability alteration. In summary, the investigations conducted in this dissertation highlight the influential role of wettability in impacting the underlying pore-scale displacement behavior and advance wettability alteration characterization during direct numerical simulations.