Numerical study of density-driven reactive flows in a fractured porous medium for CO2 storage

Abstract

Fractures play a crucial but uncertain role in trapping mechanisms for CO${}_2$ sequestration, particularly when coupled with mineral-fluid reactions. This study numerically investigates the impact of fractures at different Damköhler numbers (Da) for density-driven reactive flows in an idealized fractured porous medium model, using a discrete unified gas-kinetic scheme that accounts for porosity changes. The analysis includes single fracture scenarios (horizontal and vertical) as well as multiple intersecting fracture scenarios combining both fracture types. The study reveals that fractures exhibit similar effects to those observed in non-reactive scenarios, i.e., horizontal fractures enhance lateral mixing, leading to more uniform dissolution of CO₂ across the fracture, whereas vertical fractures concentrate CO₂ near the fracture and enabling deeper penetration into the porous medium. Numerical results further show that a high Da significantly delays the onset of convection and prolongs the duration of the “constant flux” regime. Moreover, vertical fractures enhance dissolution efficiency by increasing the constant dissolution flux by up to 10% at high Da values, thereby further facilitating CO${}_2$ penetration into the matrix. Porosity changes due to the mineral-fluid reaction confined to the upper region, with localized increases observed directly over the vertical fracture for both single and multiple fracture scenarios. Additionally, while mineral-fluid reactions have a minor effect on porosity change, they can enable up to twice the amount of CO₂ storage compared to non-reactive scenarios.