Rouhollah Fatehi

This paper presents a linear perturbation analysis of natural convection in porous media due to density change caused by dissolution of an injected carbon dioxide in saline aqueous phase. The main application is in geological sequestration of CO2 in deep aquifer. In this study, both density and viscosity of the fluid in the medium are functions of the dissolved substance concentration. Effects of concentration-dependent viscosity and density on the stability of the system are studied parametrically. By linearizing the system of equations, a set of governing equations for perturbed concentration and velocity is derived as a function of density and viscosity derivatives. Then, the eigenvalue problem is solved numerically to obtain growth rate of waves as a function of wave-number. From a quantitative analysis on the onset of instability, it is found that the system is more stable when the viscosity increases more rapidly with concentration. In addition, parametric analysis of density–concentration relationship shows that the form of density–concentration relationship affects the prediction of onset of instability. In this way, concavity of density–concentration function decreases the weight of the top layer and lowers the destabilizing effect of the layer. These findings provide a more realistic outlook to recognize the onset of convection and long-term fate of disposed gas in large-scale geological sequestration of CO2.