Mesoscopic Numerical Study of CO2 Reactive Transport in Fractured Porous Rock Formations

Abstract

This study employs a lattice Boltzmann model to investigate CO\(_2\) reactive transport in fractured porous media, focusing on the effects of Reynolds number (Re), porosity (\(\varepsilon \)), and fracture geometry. Results indicate that the steady-state average reaction rate exhibits coupled dependencies on these parameters. At low Re, the steady-state average reaction rate increases monotonically with \(\varepsilon \). In contrast, a non-monotonic relationship is observed at high Re, governed by a critical porosity threshold (\(\varepsilon _c\)). For \(\varepsilon < \varepsilon _c\), the steady-state reaction rate increases with \(\varepsilon \), while it remains constant or decreases for \(\varepsilon > \varepsilon _c\). The critical porosity \(\varepsilon _c\) decreases initially with Re before stabilizing. Similarly, the reaction rate’s dependence on Re is modulated by porosity. At low \(\varepsilon \), the reaction rate rises with Re. At high \(\varepsilon \), a critical Reynolds number (\(\textrm{Re}_\textrm{c}\)) emerges. Below \(\textrm{Re}_\textrm{c}\), the steady-state reaction rate increases with Re, but it remains invariant when Re exceeds \(\textrm{Re}_\textrm{c}\). The value of \(\textrm{Re}_c\) decreases and then stabilizes as \(\varepsilon \) increases. Furthermore, the reactive transport process is governed by two distinct regimes: diffusion-dominated and convection-dominated regimes. For the diffusion-dominated regime, variations in fracture geometry parameters (including fracture width, inclination angle, number, and cross configuration) exert negligible influence on reactive transport. Under the convection-dominated regime, however, increasing fracture width enhances reactant transport toward the downstream side of the porous medium and intensifies the spatial heterogeneity of the dissolution rate. Among the geometric factors, horizontal fractures exert the strongest influence on CO\(_2\) transport and generate the most pronounced dissolution heterogeneity, whereas vertical fractures have the weakest effect. An increase in fracture number correlates with a reduction in the dissolution rate. The effects of cross-fracture configurations on transport are highly similar to those of a single fracture.