Comparison of physicochemical properties between CO2 and CH4 nanobubbles produced by gas hydrate decomposition

Nanobubbles, known for their distinctive physicite and chemical properties, have been successfully applied in various fields. However, the basic properties of nanobubbles formed by gas hydrate dissociation remain poorly understood. In this work, a series of experiments are conducted to investigate the physicochemical properties and stability of CO2 and CH4 nanobubbles produced by hydrate dissociation. The results indicate that the average size of CO2 and CH4 nanobubbles derived from hydrate decomposition slightly increases as the static time prolongs, exhibiting the excellent stability of nanobubbles. Similar to macroscopic bubbles, the size variation of both nanobubble types exhibits a positive correlation with temperature. The absolute value of the surface zeta potential of the CH4 nanobubbles decreases with time, while the opposite is true for the CO2 nanobubbles. Moreover, the expansion in size for both nanobubble types demonstrates a negative correlation with increasing pH, whereas the zeta potential displays a positive correlation with pH. We observed that nanobubble potential is substantially influenced by metal cations within the solution, and the potential effect of CO2 and CH4 nanobubbles was preliminarily discussed by settlement tests as well. These findings may serve as valuable references for future assessments of the role of nanobubbles in reservoir seepage processes and the advancement of gas hydrate technology.