Interplay of Pore Geometry and Wettability in Immiscible Displacement Dynamics and Entry Capillary Pressure

Recent studies highlight the significant role of pore geometry and wettability in determining fluid-fluid interface dynamics in two-phase flow in porous media. However, current entry capillary pressure equations, rooted in the Young-Laplace equation, consider only cross-sectional details and apply wettability data measured on flat surfaces to complex three-dimensional (3D) pore structures, overlooking the coupled effect of contact angle and pore morphologies along the flow direction. This study employs the Volume-of-Fluid method to investigate: (a) How do combined effects of pore geometry and wettability control capillary pressure change, displacement efficiency, and residual saturations? (b) Can continuous two-phase flow be achieved at the pore scale? Through direct numerical simulations in constricted idealised-geometry capillary tubes and real pore structures, we vary the contact angle to characterise its impact on fluid-fluid interface morphology, entry capillary pressure (p^e_c), and displacement efficiency. Our results show that during the drainage, p^e_c temporarily decreases/turns negative under intermediate wettability conditions due to forced curvature rearrangement/reversal in the converging section. Local orientation angles along the flow direction are important in controlling the interface morphology and p^e_c evolution. Moreover, intermediate contact angles enhance displacement efficiency due to curvature reversal, while insufficient corner flow during imbibition causes pore snap-off of the receding fluid, leading to higher residual saturation. The results challenge conventional methods in predicting entry capillary pressure, highlighting the need for incorporating 3D geometry in predictive models. Eventually, the insights underscore the importance of considering corner flow in controlling displacement efficiency within constricted geometries in pore network modelling studies.