Storage Mechanism and Dynamic Characteristics of CO2 Dissolution in Saline Aquifers

Solubility trapping is one important storage method in CO2 geological sequestration, which is affected by many factors such as temperature, pressure, and salinity. At present, the solubility of single mineral (such as pure water, NaCl, MgCl2) solution is mostly studied, and the dynamic dissolution process under actual reservoir conditions is less studied. In this study, based on the improved experimental method, we carried out static and dynamic solubility experiments under reservoir conditions. With pore permeability measurements, scanning electron microscopy, and other experimental means, the dynamic change rule and reason for CO2 solubility were clarified. The results show that the static solubility experiment has more advantages in identifying the law of influencing factors of CO2 solubility in the short term and quickly, and the dynamic solubility experiment is more accurate in simulating the actual CO2 geological storage process change rule. Temperature is the most sensitive to solubility, followed by pressure, and salinity is almost unaffected by temperature and pressure for solubility. Under reservoir conditions, the solubility of CO2 is closer to the solubility value (3.2/100 g) after dynamic equilibrium, and the solubility of CO2 shows a dynamic process of “first decreasing, then increasing, and then balancing”, reaching the lowest at about 15 days, about 1.76/100 g. But with a longer reaction time, improving solubility values, eventually, it gradually becomes saturated after 30 days, and eventually reaches equilibrium. The equilibrium solubility is about 5% lower than the static solubility value, due to the dynamic competition between mineral dissolution and precipitation under reservoir conditions, and at the same time, “chemical retention” and “residual capture” play a key role.