Beyond wettability: Flow regime and geological heterogeneity controls on CO₂ trapping efficiency and dissolution behavior in saline aquifers

CO₂ trapping in saline aquifers is governed by the link of capillary, viscous, and gravitational forces, each modulated by wettability, flow rate, and geological structure. This study employs field-scale simulations to quantify how these parameters jointly control trapping efficiency, pressure evolution, and long-term storage security across a range of dimensionless gravity numbers ( N _Grav ). At low N _Grav , dissolution trapping is effective in both wettability states, whereas at high N _Grav , water-wet systems surpass weakly water-wet ones due to stronger capillary retention that prolongs CO₂–brine contact. Over time, a portion of the capillary-trapped CO₂ gradually dissolves, reducing the trapped fraction by 3.2 % (R_t = 0.036 % yr⁻¹) in water-wet and 0.6 % (R_t = 0.007 % yr⁻¹) in weakly water-wet systems, confirming a slow capillarity-driven transformation. Further Simulations incorporating lithological heterogeneity and fault structures reveal that geological compartmentalization changes flow regimes and trapping behavior. Moderate heterogeneity enhances both residual and dissolution trapping, while a tight, low-conductivity (1 %) fault reverses conventional wettability behavior: the water-wet case exhibits higher dissolution at both early and late times. This arises because the fault suppresses cross-fault flux and lowers gas velocity, converting a viscous-dominated regime into a capillary-controlled one. Consequently, the effective critical N _Grav for crossover behavior shifts to values exceeding ∼500, showing that structural compartmentalization can override expected wettability trends. Pressure analysis confirmed safe operation below the mechanical limit (0.9 × P _fracture = 6500 psi) with ≥50 % safety headroom at moderate rates. These results establish a mechanistic framework for safe, energy-efficient CO₂ storage, directly supporting cleaner production objectives.