Dynamic characterize of interface and mass transfer of CO2-brine during CO2 storage in saline aquifer

Abstract

Understanding the mass transfer characteristics between CO₂ and brine is essential for advancing CO₂ saline aquifer storage technology. The study visualizes supercritical CO₂ (scCO₂) dissolution into brine in porous media under high temperature and pressure by using micro-computed tomography. The dynamic evolution of interphase interface of CO₂-brine was innovatively investigated in three dimensions and quantified over time. The conclusions showed that the residual saturation of CO₂ was negatively correlated with the flow rate. Five distinct forms of CO₂ cluster evolution were identified, resulting in the non-uniform spatial distribution of the CO₂-brine interface. Then a novel classification of four interface types between CO₂ and brine was proposed and it exhibits non-monotonic evolution due to the combined effects of pore filling and snap-off events. Both local and spatial mass transfer coefficients (MTC) were calculated based on the quantified interfacial area, showing strong heterogeneity along porous media. Additionally, the local MTC of scCO₂ was found to be from 10⁻¹⁰ to 10⁻⁶ m/s, with a broader range of magnitudes compared to its gaseous state (10⁻⁹ to 10⁻⁸ m/s). Finally, the mass transfer model for trapped-phase dissolution in porous media is extended on the basis of the Sherwood number, Reynolds number and Schmidt number. Understanding the evolution of these interfaces and models of dissolution mass transfer of trapped phase can aid in predicting CO₂ behavior in saline aquifers, optimizing storage strategies, and ensuring CO₂ dissolution trapping and long-term storage stability.