Strategies for Preventing Salt Precipitation and Blockage Risks in CO2 Injection Wells: Pore-Scale Experimental Insights

In the CO₂ geological sequestration in saline aquifers, salt precipitation can lead to a decrease in reservoir permeability and porosity, severely impacting sequestration projects. While significant research has been conducted on the mechanisms of salt precipitation and remedial strategies of postprecipitation, there has been little focus on preventive strategies before salt precipitation occurs. This study designs pore-scale experiments to investigate the impact of preventive strategies on injectivity and proposes two prevention schemes: preinjection of water and CO₂ presaturated with water. The study found that preinjecting fresh water into the reservoir before injecting dry CO₂ can effectively dilute the in situ formation water and significantly reduce salt precipitation, thus maintaining good injectivity, particularly when there is almost no boundary solution in the reservoir. However, in conditions with an infinite boundary solution, as the replenishing solution continues to flow back to the inlet, the preinjection of water cannot prevent the formation of a wet salt barrier at the inlet, significantly damaging injectivity. For the CO₂ presaturated with water scheme, the study found that when low-temperature humidified CO₂ enters a high-temperature reservoir, the higher temperature increases the solubility of water vapor in CO₂, causing the formation water to evaporate and precipitate salt. Thus, it cannot prevent the formation of a wet salt barrier in the inlet. However, when high-temperature humidified CO₂ enters a low-temperature reservoir, the temperature drop causes the water vapor in the CO₂ to become supersaturated and periodically condense into fresh water, continuously flushing and diluting the formation water. Consequently, no salt precipitates in the porous structure, and good injectivity is maintained. Therefore, under specific conditions, both the preinjection of fresh water into the reservoir and the CO₂ presaturated with water schemes can effectively prevent salt precipitation, significantly mitigating the adverse effects of salt precipitation on sequestration projects.