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

Abstract 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Damk</mml:mi> <mml:mover accent="true"> <mml:mrow> <mml:mi>o</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̈</mml:mo> </mml:mrow> </mml:mover> <mml:mi>h</mml:mi> <mml:mi>l</mml:mi> <mml:mi>e</mml:mi> <mml:mi>r</mml:mi> </mml:math> number, Da ) on mixing length ( l m / l y ), dissolution flux ( F ), and onset time of convection ( t on ) are systematically investigated. In the absence of reactions, the instability is purely gravitational, with t on ∝ 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 t on , 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 t on . This non-monotonic response reveals a critical <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Damk</mml:mi> <mml:mover accent="true"> <mml:mrow> <mml:mi>o</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̈</mml:mo> </mml:mrow> </mml:mover> <mml:mi>h</mml:mi> <mml:mi>l</mml:mi> <mml:mi>e</mml:mi> <mml:mi>r</mml:mi> </mml:math> number ( Da cr ) marking the transition point. As Ra increases, Da cr 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.