Pore-scale analysis of gravity-driven flow and reaction coupling in porous media

This study employs a multi-relaxation-time lattice Boltzmann method to simulate gravity-driven convective mixing coupled with dissolution reactions at the pore scale. In homogeneous porous media, the effects of high gravitational driving strength (represented by the Rayleigh number, Ra) and varying kinetic reaction constant (represented by the Damk¨ohler number, Da) on mixing length (lm/ly ), dissolution flux (F), and onset time of convection (ton) are systematically investigated. In the absence of reactions, the instability is purely gravitational, with ton ∝ Ra−1.88, consistent with REV-scale results. When dissolution reactions are introduced, increasing Da shifts the dominant mechanism from gravitational instability to reaction–infiltration instability. In the gravity-dominated regime, stronger reactions delay ton, indicating a stabilizing effect. In contrast, in the reaction–infiltration dominated regime, strong reactions and enhanced local permeability trigger secondary interface perturbations, resulting in multiple F peaks and earlier ton. This non-monotonic response reveals a critical Damk¨ohler number (Dacr) marking the transition point. As Ra increases, Dacr decreases from 38 to 11, highlighting the synergistic role of gravity and reaction strength in destabilizing the system. In comparison, simulations in irregularly distributed porous media reveal that the mechanism responsible for multiple F peaks, previously identified in homogeneous cases, can also occur. However, its manifestation depends strongly on porosity: at lower porosity, reaction–infiltration instability enables multi-stage mass transfer, whereas at higher porosity gravitational instability dominates, suppressing the multiple-peak behavior. These findings provide new insights into interfacial dynamics and reactive transport relevant to subsurface carbon storage.