Study of the Surface Morphology of Gas Hydrate

Study of the surface morphology of gas hydrate is of great importance in understanding its physical properties and occurrence. In order to investigate the surface morphology of different types (sI and sII) and occurrences (pore-filling and fracture-filling) of gas hydrate, both lab-synthesized and drilled-gas hydrate samples were measured using cryo-scanning electron microscopy (cryo-SEM). Results showed that the surface of sI hydrate was relatively smooth, and spongy nano-pores (200-400 nm) gradually occurred at the surface during continuous observation. The surface of sII hydrate was more compact, showing a tier-like structure. Hydrate occurred in quartz sand and usually filled the pores of the sediments and both hydrate and sediments were cemented with each other. SEM observation of the gas hydrates collected from the South China Sea showed that the surface morphology and contact relation with sediments varied with hydrate occurrence. For instance, hydrates dispersed in sediments mainly filled the pores of the sediments. The existence of microorganism shells, such as foraminifera, was beneficial to the formation of gas hydrate. When hydrate occurred as a massive or vein structure, it was easily distinguished from the surrounding sediments. The surface of hydrate with massive or vein structure showed two distinct characters: one was dense and smooth, the other is porous (several to tens of micrometers in diameter). The occurrence of different hydrate morphologies was probably caused by the supplement rates of methane gas.