Pore-scale salt precipitation during CO2 injection: How additives and interfacial tension govern crystallization?

Salt precipitation during CO 2 injection into saline aquifers can significantly impair near-wellbore injectivity, yet pore-scale crystallization mechanisms remain poorly resolved. This microfluidic study investigates how solid–liquid interfacial properties and fluid composition control residual brine distribution, evaporation kinetics, and crystal coverage. A total of 76 replicated, position-resolved experiments were conducted at 5 MPa using eight fluids: three NaCl solutions (1, 2.5, 5 mol kg − 1 ), a natural geothermal brine, and four additive-modified systems (surfactant, co-solvent, pH modifier, and reactive ammonia). Results are interpreted through a three-stage mechanistic framework. First, CO 2 breakthrough sets the residual brine saturation ( S w ), controlled mainly by interfacial tension and capillary-driven displacement. Second, continuous CO 2 flow evaporates immobile brine via convective mass transfer, producing crystals within brine pools and through capillary-fed growth beyond them. Third, the final crystal coverage ( X c ) depends on the initial brine inventory and salt concentration; flow rate affects only onset timing and evaporation, not the equilibrium outcome. Thus, flow-rate-controlled kinetics are decoupled from flow-rate-insensitive outcomes in this capillary regime. Although spatial crystal patterns vary probabilistically, total coverage remains reproducible. Additive effectiveness for reducing X c follows: isopropyl alcohol (56% reduction) > alkylbenzene sulfonate (22% reduction). Potassium hydroxide increases coverage by 22% due to enhanced nucleation. These effects map onto changes in S w , showing that reducing residual saturation is the primary mitigation pathway. Natural brine behaves equivalently to synthetic NaCl, supporting common laboratory simplifications. Overall, the study establishes quantitative links between fluid properties and salt-precipitation dynamics, providing benchmark datasets for model validation and additive-based mitigation design.