Morphological Change of Hydrate Caused by Ostwald Ripening and Sintering

Natural gas hydrates (NGHs) accumulate over hundreds to thousands of years in sediments and are a significant carbon reservoir on Earth. Synthetic hydrates, formed within minutes to days to mimic natural NGHs, fail to provide sufficient insight into hydrate morphological changes that occur over a long period. In this study, we present a novel micromodel, combined with a digital microscope, to observe tetrabutylammonium bromide (TBAB) hydrate formation (10 wt %) in porous media and open space over a period of 2 months, facilitating the discussion of time-resolved hydrate behaviors. The results indicate that TBAB hydrate can mimic methane hydrate formation, Ostwald ripening, and sintering from dissolved gas, while simultaneously accelerating these processes. Hydrate Ostwald ripening and sintering were observable several weeks after the onset of formation, leading to a decrease in the particle number. Simultaneously, the particle size increased significantly without alteration of the overall hydrate saturation. This process heterogeneously altered the hydrate morphology and enhanced flow channels. These findings explain the higher permeability characteristics observed in natural sediments compared to those in synthetic samples.