Hydrate Formation and Methane Mass Transfer Characteristics in Static Systems of Pure Water and Saline Water with Varied Initial Dissolved Methane Concentrations

Methane seepage from deep-sea seabeds is an important carbon and energy source in the ocean, exerting significant impacts on marine and global environments and ecosystems. The conversion characteristics of dissolved methane to solid hydrates not only influence the variation pathways of seeping methane but also play a crucial role in methane's biological and chemical transformation processes. The dissolved methane concentration around seafloor methane seepage vents varies with distance, yet the hydrate transformation characteristics with different concentrations of dissolved methane remain unclear. In this study, the hydrate formation and methane mass transfer characteristics in static systems of pure water and saline water with different initial dissolved methane concentrations were investigated. The experimental results indicated that the slow mass transfer process of methane molecules in the water phase was a key limiting factor for the conversion of dissolved methane into hydrates. Compared to pure water, the lower mass transfer coefficient of methane in saline water further restricted the hydrate formation and also slowed the process of methane gas dissolution. Although differences were observed in the growth status of interfacial hydrates for different experiments, resulting in smooth or needle-like hydrate membranes, this did not significantly affect the conversion of gaseous methane to hydrates. The findings of this study provide foundational data and theoretical support for understanding the fate of methane in systems with varying initial dissolved methane concentrations.