Localized CO2-induced salt precipitation in unconsolidated saline porous media: Insights from quasi-2D flow cell experiments

The transition to net zero emissions is crucial for mitigating climate change, and Geological Carbon Storage (GCS) plays a pivotal role in securely storing in deep underground formations. However, injecting into saline aquifers presents challenges, such as salt precipitation, which can reduce permeability and hinder migration within the porous medium. Quasi-2D FluidFlower flow-cell experiments (hereafter, the flow cell) were performed to analyze migration patterns under different salinity levels and potential salt-precipitation phenomena. The experiments were carried out under controlled laboratory conditions (1 atm and 20.0 ± 1 . 5 ° C ). injection was performed with coarse sand (1.0 to 2.0 mm) and medium sand (0.36 to 0.71 mm) at a rate of 10 ml/min in various saline fluids (synthetic solutions with salinities of 0.0, 33.6, 64.7 g/L and natural solutions with salinities of 29.3 and 74.5 g/L). The results indicated that dissolved and reacted with the pH indicator solution, generating color zones that transitioned from yellow to green corresponding to different concentrations of . Furthermore, gaseous displaced water and dissolved inorganic carbon species, laterally expanding the plume within the porous medium and promoting salt nucleation. The study found that natural fluids required longer times to form dissolved zones due to their higher buffering capacity compared to synthetic solutions. Higher-salinity cases promoted evaporite deposition primarily as surface crystals in gas-dominated zones, whereas porous-medium (grain-scale) deposits were only observed for the highest-ionic-strength synthetic brine (FB). These findings improve our understanding of behavior across different salinities, providing valuable information for the underground storage in saline aquifers. • CO 2 migration in unconsolidated sands under synthetic and natural brine conditions. • Gaseous CO 2 injection displaces formation brine and drives CO 2 plume expansion. • Dissolved CO 2 zones developed more slowly in natural brines than in synthetic ones. • High-salinity conditions enhanced salt precipitation in synthetic and natural brines.