Cyclic injection of CO 2 into a saline aquifer with extended interface

Cyclic CO2 injection is considered to be an effective method to maximise CO2 dissolution in hydrocarbon reservoirs (Reznik et al., 1984; Monger et al., 1991) and saline aquifers (Zhang and Agarwal, 2012; Dusseault et al., 2012). Gravity override and evolution of a transition zone have large effects on the development of a saturation transition zone between the pure host fluid and the injected gas. In this paper, equivalent relative permeability functions are derived to address the effect of gravity override, allowing reduction of the problem dimension from 2D to 1D. An analytical solution for saturation distribution in a cyclic drainage-imbibition process is obtained. To incorporate the solubility of CO2 in the aqueous phase, a one-way coupled approximation is used and a numerical solution is proposed for derivation of compositional distribution of the chemical species. Information about saturation distribution from the analytical solution provides saturation distribution over time and distance, and this is substituted in the concentration distribution equation. In contrast to previously well-studied analytical solutions (e.g., Orr, 2007), this hybrid scheme includes the effect of kinetic mass transfer and dispersion, and provides a reasonable approximation for saturation-concentration distribution during injection.