Scaling Up FluidFlower Results for Carbon Dioxide Storage in Geological Media

Abstract

The partial differential equations describing immiscible, but soluble, carbon dioxide (CO₂) displacement of brine in saline storage formations are developed including mass transfer across the CO₂–brine interface. Scaling relationships for characteristic time among laboratory and representative storage formation conditions are found upon assumption that free-phase CO₂ transport during injection is dominated by pressure-driven flow. The implication is that an hour in the FluidFlower (room-scale visual model) scales to hundreds of years of elapsed time in the storage formation. The scaling criteria permit extrapolation of the effects of changes in parameters and operating conditions. Interphase mass transfer allows CO₂ to saturate the brine phase and the finite time of such mass transfer results in substantial time to approach equilibrium. Significant mixing of CO₂ dissolved into formation brine with original brine is found experimentally and is also predicted. The magnitude of onset time for buoyancy-driven fingers that enhance mixing of CO₂ is typically only a fraction of the duration of CO₂ injection and in general agreement with theoretical analysis in the literature. Predictions for onset time of convective mixing at representative storage formation conditions, likewise, teach that the onset time for fingering is significantly less than the duration of CO₂ injection in some cases. The implications of this observation include that mixing of CO₂ with brine and the subsequent settling due to gravity are relatively rapid and coincide with the period of active CO₂ injection.