Investigation of Pore-Scale Evaporative Drying, Salt Precipitation and Crystallization Migration in CO2 Injection Process by a Lab-On-A-Chip System

Abstract In this study, a self-designed microchip system was used to visually study the pore-scale salt crystallization and migration, and a high-performance optical microscope was used to dynamically observe the salt precipitation process and results. The results show that pore-scale salt crystals mainly precipitate in the residual water phase, and mainly present two forms of occurrence, large-grained salt crystals and small-grained aggregated crystals, respectively. In addition to growing in the brine phase, large-grained salt crystals also nucleate and grow at the gas-liquid interface, and the maximum salt crystal size can reach the order of the pore size. This phenomenon was discovered for the first time and has not been mentioned in the existing literature. In addition, this study also observed an interesting phenomenon. The salt crystals formed in the wetting brine film and the brine phase can migrate under the combined influence of displacement pressure and capillary force, and eventually accumulate and precipitate inside the pores. Injection flow rate and salinity have a strong influence on the pore-scale salt crystallization kinetics. There is a critical value for the injection flow rate, and the critical injection rate causes the salt precipitation to be significantly aggravated. Under the same injection flow rate, an increase in salinity leads to an increase in the amount of salt precipitation.