Bubble Evolution and Its Effects on Methane Hydrate Formation in a Restricted Space

Based on the in situ observation of methane hydrate formation in restricted spaces by confocal Raman imaging microscopy, a bubble intrusion mechanism is proposed. Hydrates are found to form both at the gas–water–solid triple-phase contact line and at the gas–water interface. Hydrates at the triple-phase contact line can form capillary channels with solid surfaces. The formed capillary channels can force the water inside the droplet to diffuse outward, leading to shrinkage of the droplet edge and generation of gas bubbles inside the droplet. Hydrates can then rapidly form at the bubble–solution interface. With the method of Raman imaging, gas channels are found in the interfacial hydrates, acting as bridges connecting bubbles and the surrounding solution. Through these gas channels, methane gas can dissolve rapidly into the solution in the droplets, thereby promoting the formation of hydrates in the droplets.