Convective instability of CO2 sequestration in a thermally anisotropic porous layer: A first-order Brinkman–Darcy–Kelvin–Voigt model

The present study examines the onset of double-diffusive convection in a thermally anisotropic horizontal porous layer saturated with a viscoelastic fluid governed by the first-order Kelvin–Voigt model. This framework is motivated by applications in carbon dioxide (CO2) sequestration in deep saline aquifers, which is an essential strategy for minimizing greenhouse gas emissions in the atmosphere. When CO2 dissolves into brine, the fluid density rises, which can destabilize the system and trigger the onset of convection. In addition to driven density differences, the dissolved CO2 is assumed to undergo a first-order chemical reaction, adding reactive effects into the stability mechanism. The eigenvalue problems arising from the linear and nonlinear stability theories are solved numerically to obtain stability thresholds. The stability of the system is strongly influenced by the interplay among viscoelastic effects, anisotropic thermal and solutal diffusivity, and reaction rate (characterized by the Damköhler number). The results reveal that viscoelastic memory diffusion and chemical reaction interact to modify the onset of convection: memory effects suppress velocity perturbations and elevate the critical stability threshold, while the reaction rate modifies the solutal buoyancy field, leading to both stabilization and non-monotonic behavior in certain parameter regimes. The present work provides a clear understanding of how viscoelastic rheology and reactive transport jointly influence the convective instability in thermally anisotropic porous media, with implications for identifying favorable reservoir conditions for safe and efficient CO2 storage.