Aquifer-on-a-Chip: understanding pore-scale salt precipitation dynamics during CO2 sequestration

Abstract

In this study, we develop a lab-on-a-chip approach to study pore-scale salt precipitation dynamics during CO₂ sequestration in saline aquifers—a challenge with this carbon management strategy. Three distinct phases—CO₂ (gas), brine (liquid), and salt (solid)—are tracked through microfluidic networks matched to the native geological formations. The resulting salt formation dynamics indicate porosity decreases of ∼20% in keeping with large scale core studies. At the network scale, the salt precipitation front moves at a constant velocity, ∼2% that of the superficial CO₂ velocity in this case. At the pore-scale, we observe two dominant types of salt formation: (1) large bulk crystals, on the order of the pore size (20–50 μm), forming early within trapped brine phases; and (2) polycrystalline aggregated structures, ranging over broad length scales, forming late in the evaporation process and collecting/projecting from the CO₂–brine interface. Together, these two salt formation mechanisms show particular propensity for pore blockage and reduced carbon storage capacity.