Pore-scale study of brine evaporation and salt precipitation mechanisms during CO₂ injection

Carbon storage in saline aquifers is a prominent geological method for reducing CO 2 emissions. However, salt precipitation within these aquifers can significantly impede CO 2 injection efficiency. This study examines the mechanisms of salt precipitation during CO 2 injection into fractured matrices using pore-scale numerical simulations informed by microfluidic experiments. The analysis of varying initial salt concentrations and injection rates revealed three distinct precipitation patterns, namely displacement, breakthrough and sealing, which were systematically mapped onto regime diagrams. These patterns arise from the interplay between dewetting and precipitation rates. An increase in reservoir porosity caused a shift in the precipitation pattern from sealing to displacement. By incorporating pore structure geometry parameters, the regime diagrams were adapted to account for varying reservoir porosities. In hydrophobic reservoirs, the precipitation pattern tended to favour displacement, as salt accumulation occurred more in larger pores than in pore throats, thereby reducing the risk of clogging. The numerical results demonstrated that increasing the gas injection rate or reducing the initial salt concentration significantly enhanced CO 2 injection performance. Furthermore, identifying reservoirs with high hydrophobicity or large porosity is essential for optimising CO 2 injection processes.