Seabed methane seepage is a ubiquitous phenomenon in deep-sea environments and on continental margins, affecting the ocean and global carbon cycle. As one of the world’s largest methane reservoirs, natural gas hydrate (NGH) is an important barrier for methane capture. However, the formation of hydrate shells on the surface of CH4 bubbles seeping into the water column may also assist in the migration of methane to the shallow sea and even into the atmosphere. Therefore, it is necessary to reveal the formation characteristics of hydrate film on the surface of CH4 bubble. In this work, the evolution of CH4 hydrate formation on a bubble surface and the dissolved CH4 concentration in the surrounding aqueous phase were simulated in different simulated ocean depth environments by using the suspended bubble method. The results showed that higher subcooling for hydrate formation leaded to smoother initial hydrate film, and the hydrate bubble was prone to flexible collapse due to faster gas consumption. In contrast, for dense and thick hydrate films, the occurrence of pressure difference between the internal and external of the film can lead to brittle collapse of the hydrate shell. The Raman measurement results basically corresponded to the morphological evolution phenomenon. In addition, it was found that the formation of hydrate film on the bubble surface weakened the mass transfer from the gas phase to the liquid phase, making the CH4 dissolution rate almost equivalent in different pressure environments. This work can provide important fundamentals for assessing the flux of methane leakage into shallow water in the marine environment.
Keywords CH4 hydrate, gas bubble surface, subcooling, morphology, Raman