The impact of porous microstructures of gas hydrates on their macroscopic properties

Methane hydrates from both sub-permafrost and sea-floor occurrences show a very particular microstructure as evidenced by scanning-electron-microscopy. These hydrates are frequently porous with typical pore sizes ranging from 100 nm to 500 nm, occasionally reaching 1 mum. The pores are predominantly closed with only occasional openings between them and filled with methane gas. The gas-filling will affect the physical properties of gas hydrates. In particular, it can be expected that the attenuation of elastic waves is increased. We suggest that the repeatedly observed combination of high seismic velocities and high attenuation in gas-hydrate-bearing sediments may well be attributed to the presence of gas in the porous microstructures.