Stability and Behavior of Bulk Nanobubbles Under Reservoir Conditions

Compared with microbubbles, nanobubbles exhibit superior stability, higher specific surface area, and smaller size. These characteristics have increasingly attracted the attention of petroleum researchers. However, existing literature lacks studies on nanobubble concentration and size under harsh reservoir conditions. To address this gap, this study conducted nanoparticle tracking analysis (NTA) to evaluate nanobubble concentration and size under varying salinity levels, reservoir pressures, high temperatures, and pH conditions. The results indicate the existence of a critical salinity threshold: Above this threshold, nanobubble concentration gradually decreases, whereas at lower salinity levels, the concentration initially decreases before increasing again. The particle size generally trends downward with increasing salinity but with limited variation. Additionally, nanobubble concentration decreases as the valence state of dissolved salts increases, while particle size increases correspondingly. At 30 MPa, nanobubbles remain present, with an increase in concentration and a reduction in size compared with atmospheric pressure conditions. Temperature has almost no effect on the particle size of nanobubbles. Even at 100°C, nanobubbles will not completely disappear. Furthermore, higher pH levels correlate with increased nanobubble concentration, though the impact on particle size remains minimal. These findings provide a foundational understanding of nanobubble behavior under harsh conditions, facilitating further research into their potential applications in reservoirs.