Progressive wettability alteration during high-flux waterflooding: Pore-scale oil-phase mobilization pathways and pore–throat structural control

Progressive wettability alteration (PWA) under high-flux waterflooding reorganizes residual-oil topology, yet the pore-scale mobilization pathways remain incompletely resolved. We combine MnCl2-assisted D2O nuclear magnetic resonance core flooding [pore-area (PA) = 50 m and Ca = 1.805 × 10−6] with two-phase lattice Boltzmann simulations in which wettability evolves as a PA-controlled, spatially non-uniform boundary condition. The short-T2 signal tracks discontinuous remnants (films and droplets). As wettability shifts from oil-wet toward weakly water-wet conditions, discontinuous oil exhibits retention followed by mobilization, concurrent with partial remobilization of connected oil; the effect is stronger in higher-permeability cores. Simulations attribute this behavior to two coupled force balances: for trapped ganglia, a spatially non-uniform, time-evolving contact angle perturbs the balance between geometry-imposed capillarity and the driving pressure gradient; for wall-bound films, viscous shear competes with wettability trapping, and PWA weakens trapping to promote beading, breakup, and detachment along high-flux pathways. We characterize the relative pace of wettability alteration vs preferential-pathway organization using Π, defined as the PA required for substantial wettability alteration divided by the PA at water breakthrough. High Π (>2.5) yields a delayed, long-tail response dominated by film retention and late-time remobilization, whereas reducing Π by 20× decreases film-related events by >40% and shifts the dominant response toward invasion-concurrent ganglion mobilization. Pore–throat structure further controls Π and the exposure footprint: well-connected structure #1 supports multi-spot alteration and stronger late-time reactivation, yielding a 7.2-point efficiency gain at PA = 2200 μm. In strongly heterogeneous structure #3, earlier breakthrough localizes flow into a shear-dominated channel, limiting the gain to 2.2 points.