Why is it critical to revisit significance and consequences of salt precipitation during CO2 injection?

Abstract

Among the candidates for CO2 sequestration, deep saline aquifers are considered the best option because of their storage capacity and proximity to emission sources. Injection of large volumes (million tons scale) of supercritical CO2 into the geological formations causes evaporation of formation water near wellbores and precipitation of salt crystals inside the porous medium. CO2-induced salt precipitation can substantially threaten sequestration in saline aquifers. Most available experimental, numerical and theoretical works have focused on predicting the salt's location and amount. However, less attention is given to the precipitation physics, growth dynamics, and behavior of the fluid-solid interface near the evaporation/precipitation front. We report a series of experiments to provide new insights, beyond the current understanding, into the dynamics of brine evaporation and salt growth and to challenge the current understanding that might not be entirely representative of the field conditions. The research outcome highlights the interplay of complex processes (some of which are not yet fully characterized) crucial in investigating salt precipitation induced by million-tons-scale CO2 injection. The observed characteristics call for further in-depth investigation because, in the context of subsurface CO2 storage, we need to redefine how we see injectivity impairment due to salt precipitation.