Convective dissolution of carbon dioxide in saline aquifers

TLDR

Geological CO₂ storage reduces anthropogenic emissions, and its security is enhanced by CO₂ dissolution into brine, which creates stable stratification. The study introduces a new analogue fluid system that reproduces the convective behaviour of CO₂‑enriched brine. Convection driven by density increases with CO₂ saturation determines the dissolution rate, and the authors use a new analogue fluid system to reproduce this behaviour. Experiments and simulations reveal that convective flux scales as the Rayleigh number to the 4/5 power, and a scaling argument incorporating lateral diffusion explains this nonlinear relationship, predicting that convective dissolution can significantly enhance storage security.

Abstract

Geological carbon dioxide (CO 2 ) storage is a means of reducing anthropogenic emissions. Dissolution of CO 2 into the brine, resulting in stable stratification, increases storage security. The dissolution rate is determined by convection in the brine driven by the increase of brine density with CO 2 saturation. We present a new analogue fluid system that reproduces the convective behaviour of CO 2 ‐enriched brine. Laboratory experiments and high‐resolution numerical simulations show that the convective flux scales with the Rayleigh number to the 4/5 power, in contrast with a classical linear relationship. A scaling argument for the convective flux incorporating lateral diffusion from downwelling plumes explains this nonlinear relationship for the convective flux, provides a physical picture of high Rayleigh number convection in a porous medium, and predicts the CO 2 dissolution rates in CO 2 accumulations. These estimates of the dissolution rate show that convective dissolution can play an important role in enhancing storage security.