Impact of Pore-Scale Geometry on Waterflooding Efficiency: A Computational Fluid Dynamics-Based Investigation Using Direct Numerical Simulation

This study investigates the role of pore-scale geometry (pore size, throat dimensions, connectivity) and oil-wet conditions in governing waterflooding efficiency. By analyzing three distinct pore networks (coordination numbers 3, 4, 6), the work establishes how pore architecture and wettability dictate the dynamic interplay between capillary and viscous forces, linking microscale interfacial dynamics to macroscopic displacement patterns. The scope provides actionable insights for optimizing water flood designs in heterogeneous, oil-wet reservoirs through pore-topology-aware simulation strategies. High-resolution computational fluid dynamics (CFD) simulations were conducted in the OpenFOAM solver, employing SnappyHexMesh to generate Cartesian grids for three-pore geometries with coordination numbers 3, 4, and 6. Direct Numerical Simulation resolved multiphase flow dynamics via the Volume of Fluid (VOF) method, incorporating wettability, capillary forces (modeled by the Young-Laplace equation), and viscosity contrasts. The pressure implicit with the splitting of the operator's algorithm coupled pressure-velocity fields, while a compression term in the VOF advection equation minimized interface coverage. The Brackbill number constrained time steps (Δt = 10 μs) to suppress spurious currents. To analyze displacement efficiency, post-processing quantified saturation profiles, pressure evolution, and velocity fields. Simulations demonstrate that pore connectivity and diameter critically influence displacement efficiency. Higher coordination numbers (e.g., 6-sided connected pores)enhance sweep efficiency by enabling capillary-driven flow pathways, accelerating water propagation after initial imbibition. In oil-wet porous media, small-pore geometries resist water infiltration but sustain capillary-driven drainage, while larger pores favor viscous displacement. Pressure profiles reveal transient dominance of capillary forces over viscous forces, particularly in low-connectivity networks. The 6-connected network achieved 50% oil saturation decline and superior displacement efficiency due to optimized capillary-driven pathways compared to low-connectivity systems. These findings highlight that macroscopic recovery is governed by pore-scale architecture, necessitating geometry-aware reservoir models to predict fluid behavior. The study concludes that optimizing waterflood strategies in oil-wet, heterogeneous formations requires prioritizing pore connectivity and alignment of capillary-viscous force balances. This work provides novel insights by coupling DNS-level CFD with diverse pore geometries to quantify how coordination number and oil-wet conditions dictate capillary-viscous force interaction. Unlike homogenized models, it establishes a predictive link between pore-scale topology and recovery efficiency, offering guidelines to tailor waterflood designs to reservoir-specific pore architecture—a critical gap in current simulation practices.