Salt Precipitation Model of CO₂ Injection in Saline Aquifer Considering Influence of Capillary Force

This study modifies the CO₂ fractional flow equation by considering capillary force, brine evaporation, and CO₂ dissolution in brine. Retardation factors and similarity variables are introduced to characterize the saturation distribution and migration distance of CO₂ in saline aquifers. A quantitative evaluation model for salt precipitation during CO₂ injection into saline aquifers is established. The influences of capillary force, gas composition, rock wettability, formation pressure, and salinity on salt precipitation and CO₂ migration are analyzed. The results indicate that capillary force increases salt precipitation in the dry-out region while reducing its spatial extent. As the nitrogen content in the gas composition rises, both the amount of salt precipitation and the extent of the dry-out region decrease, whereas the two-phase zone expands. An increase in formation pressure alters the fractional flow curve and retardation factors, consequently enhancing salt precipitation. Higher irreducible water saturation and salinity result in increased salt precipitation within the dry-out region. This suggests that more water-wet rocks and highly saline aquifers are prone to more extensive salt precipitation.