Pore-Scale Modeling of Wettability Alteration Induced by Low Salinity Water in Carbonates

Wettability alteration is considered one of the primary mechanisms for enhanced oil recovery. Within this class, low-salinity water (LSW) flooding is regarded as a promising method due to its advantages of low cost and environmental friendliness. However, its physicochemical effects at the oil-water-rock contact line, and their impact on contact line dynamics, remain poorly understood in carbonates. In this work, we propose a pore-scale wettability alteration model that exhibits physical scalability based on the Lattice Boltzmann Method, which couples multiphase flow, solute transport, physicochemical reactions and Cassie-Baxter effects. We have performed theoretical analysis to identify a key dimensionless parameter at the three-phase contact line. By examining spontaneous imbibition in a channel, we elucidated how adsorption kinetics at the contact line affect fluid dynamics. To assess the model's ability to interpret experimental phenomena, we compared the simulation results to the experimental results of oil droplet movement responding to LSW on carbonate substrates. We also simulated multiphase flow in a carbonate microfluidic chip which agrees well with the experiments, indicating that the contact-line adsorption rate is markedly reduced in the vicinity of corners. The calibrated model parameters are then used to evaluate the impact of LSW-driven spontaneous imbibition on oil recovery in a 3D pore-scale model of an Estaillades limestone sample. The study revealed that, oil aging caused by the interaction between formation brine and carbonate rock, along with a high oil or water phase viscosity, can significantly weaken the low-salinity effect on oil recovery. In addition, with a high initial formation water saturation, the substantially longer three-phase contact line length can markedly enhance the low-salinity effect on oil recovery. Overall, this study addresses the multiscale contact line phenomena and underscores the pivotal role of the three-phase contact line in controlling wettability alteration and associated oil recovery in carbonates.