The effect of heterogeneity and gravity on the salt precipitation in CO2 storage simulations

The salt precipitation from the dry-out process has a profound effect on the injectivity of the injection well during carbon dioxide (CO₂) storage in deep saline aquifers. In laboratory tests, researchers neglected the effect of gravity on salt precipitation and replaced the fully heterogeneous models with a simplified fracture model. We built three fully heterogeneous models and a fracture model to do the numerical simulation. In addition, it was much easier to add gravity in the numerical simulation than the laboratory experiment to study gravity effect on salt precipitation. The collective effect of gravity and heterogeneity on salt precipitation was also studied. Simulation results showed that: The gravity effect significantly increased the solid saturation (S_s) at the injection well in the homogeneous model, changing the position of the injection well can change the distance that gravity can act and change the amount of salt precipitation; Fracture near the injection well caused an abnormal increase in the value of S_s, the heterogeneity of the rock also affected the amount of the salt deposit, the stronger the heterogeneity, the more the salt precipitates; Gravity and heterogeneity showed mutual resistance relationship when considering the collective effect of gravity and heterogeneity on S_s; Gravity effects reduced the amount of salt deposited in the fracture model; At low CO₂ injection rate (q), gravity force dominated the CO₂ flow, the increased rock heterogeneity suppressed the production of salt precipitates; At high q, viscous force dominated flow, increased heterogeneity increased salt precipitation.