Interplay of capillary, viscous, and gravity forces on salt precipitation and injectivity loss during CO2 storage in saline aquifers

Abstract

Salt precipitation during CO 2 injection into hypersaline aquifers can significantly impair injectivity. Understanding the controls on the magnitude and spatial distribution of salt precipitation is therefore critical. Here, we use TOUGH3 model to systematically investigate the coupled interplay of capillary, viscous, gravity, and reservoir layering in controlling salt-induced permeability impairment. The model has been validated against core-flooding experiments. Results show that capillary-driven brine backflow and gravity-driven brine segregation jointly govern salt precipitation in the near-well region. In layered formations, strong permeability contrasts between high- and low-permeability layers enhance capillary-driven brine backflow, while the low-permeability layers act as persistent brine sources, sustaining brine supply and promoting salt accumulation in adjacent high-permeability injection layers. Under capillary-dominated conditions, significant injectivity reductions can occur as a result of highly localized salt deposition. Increasing the flow rate, however, can suppress capillary-driven backflow, promote expansion of the dry-out region, and thereby reduce injectivity impairment. Finally, the numerical results were used to develop injectivity-loss maps as a function of the capillary and Bond numbers, which provide a framework for designing appropriate CO 2 injection rates.