Unraveling salt precipitation mechanisms in geological CO2 storage: Insights into dominant driving forces

Salt precipitation during geological CO2 storage (GCS) in saline aquifers can impair the injectivity of large-scale projects. Laboratory studies indicate that this process is sensitive to capillary force, but scaling-up to field conditions is complex due to radial flow, gravity, and geological heterogeneity. This study utilizes 3D simulations to characterize salt precipitation mechanisms in realistic storage formations. Non-dimensional groups, e.g., capillary number (Ca) and gravity number (Gr), are used to characterize the relative impact of capillary, viscous, and gravity forces on salt formation. Three distinct regimes emerge for homogeneous systems: 1) capillary-dominated regime for Ca < 1 with severe salt precipitation at the inlet; 2) viscous-dominated regime for Ca > 1 and Gr < 0.2 with low-to-moderate salt precipitation; and 3) gravity-dominated regime for Ca > 1 and Gr > 0.2 where gravity override leads to localization of salt deposits inside the reservoir. The Ca-Gr regimes generally hold for heterogeneous systems. Additional complexity includes increased salt precipitation in high-permeability zones due to lower Ca enhanced by capillary-induced imbibition of saline water from low-permeability zones. Tortuous flow paths can also emerge, further exacerbating pressure build-up. These novel characterizations can assist practitioners in designing mitigation strategies for injectivity impairment in large-scale operations.