The formation of meso‐ and macroporous gas hydrates

Abstract

Abstract. We present results of experimental studies on the formation of gas hydrates (clathrates) at conditions of geophysical interest. Clathrate hydrates formed by a reaction of gas at ice Ih surfaces are always found to be mesoporous to macroporous with pores sizes between 100 to 400 nm and pore volumes of approximately 25-40% for CH4, Ar and N2 hydrate, and smaller pores of 20 to 100rim with a porosity of approximately 10-20% for CO2 hydrate. The three-dimensional sponge-like microstructure occurs in single crystalline grains of typically a few •um size and was observed by field-emission scanning electron microscopy. It forms over a wide range of p-T conditions below the ice Ih melting. The porous microstructure is stable for at least several months, even close to the clathrate decomposition, and is proposed to be formed by local differences in the energy balance between hydrate formation and ice decompositon. The results presented are considered of potential major importance for the understanding of the behaviour of natural gas hydrates found e.g. in polar ice sheets and permafrost regions, and also in some celestial bodies.

Biochemical reaction and diffusion in seafloor gas hydrate capillaries: Implications for gas hydrate stability

“…Nuclei sizes were determined to be ∼80 nm (Dearman, 2007). The diameter values are similar to those reported by Kuhs et al (2000) where cold-stage electron microscopy was used for the determination of capillary sizes in methane and other hydrates. Dearman et al (2008) further proposes a heterogeneous nucleation mechanism for gas hydrates in saturated porous media with adsorbed biosurfactants whereby smectite particles slough from a clay mass agglomerate, diffuse through hydrate capillaries, and nucleate additional hydrate clusters.…”

Bacteria and Archaea Physically Associated with Gulf of Mexico Gas Hydrates

“…However, CH 4 , Ar, N 2 , and CO 2 can all form highly porous (as high as 40% porosity), "sponge-like" gas hydrates (23). Typical pore sizes are 100 to 400 nm for CH 4 hydrates, with occasional channels on the order of a few micrometers.…”

“…We believe that it is likely that the microbial communities described here are active within the gas hydrates. High porosity of methane gas hydrate (pore sizes of 100 to 400 nm and pore volumes of approximately 25 to 40% [23]) allows potential substrates (e.g., sulfate) to enter and products of microbial metabolism (e.g., sulfide) to exit the gas hydrate structure without difficulty. Some pores may even be large enough for microbes to freely enter and leave the superstructure of the solid gas hydrate.…”

Morphological and Compositional Characterization of Self‐Preserved Gas Hydrates by Low‐Vacuum Scanning Electron Microscopy

“…[8,11,14] Scanning electron microscopy (SEM) has been used to investigate microstructures of gas hydrates and hydrate-ice mixtures. [15,16] Stern et al [12] conducted SEM observations of partly dissociated methane hydrate particles. They reported a lack of evidence for development of ice-coating around individual hydrate grains.…”