Non-Equilibrium Behavior of CO2 Bubble Evolution Under Dynamic Pressure Conditions

Abstract

Abstract Understanding the dynamic behavior of dissolved and free-phase CO2 is critical for ensuring the long-term security of geological carbon storage. While equilibrium solubility governs the thermodynamic limits of CO2 dissolution, transient pressure changes can induce non-equilibrium exsolution and delayed redissolution that remain poorly quantified. In this study, we experimentally investigate the kinetics of CO2 exsolution and dissolution under controlled dynamic pressure conditions using a transparent, confined acrylic model filled with CO2-saturated water. A repeatable depressurization–repressurization cycle was applied at identical rates to isolate kinetic effects from thermodynamic driving forces. High-resolution imaging combined with a custom Python-based image analysis workflow enabled time-resolved quantification of bubble count, equivalent radius, and total gas volume. Results demonstrate a pronounced rate asymmetry between exsolution and dissolution, with bubble formation occurring approximately three times faster than dissolution. Exsolution initiated only after reaching a supersaturation ratio of approximately 1.5–1.6, well below equilibrium solubility predictions, indicating kinetic control of nucleation. During repressurization, a distinct pressure hysteresis and residual gas persistence were observed, reflecting interfacial mass-transfer resistance and diffusion-limited dissolution. These findings provide direct experimental evidence that CO2 phase transitions in aqueous systems under transient pressure are governed by kinetic constraints rather than equilibrium behavior. The results have important implications for geological carbon storage, particularly in scenarios involving pressure drawdown, storage management, and long-term storage integrity. The study uses high-resolution imaging and custom Python-based analysis to visualize CO2 exsolution and dissolution, revealing kinetic control of nucleation and pressure hysteresis. This approach provides insight into CO2 behavior with significant implications for geological carbon storage and climate change mitigation.