Gas hydrate dissociation affecting the permeability and consolidation behaviour of deep sea host sediment

Gas hydrate dissociation is known to affect the permeability and the mechanical properties of the deep sea host sediments. Sediment permeability and compressibility changes occurring during hydrates dissociation might put its integrity under risk. The aforementioned effects were studied experimentally on treated clayish sediments, which were retrieved from the Amsterdam subsea mud volcano (MV). The Amsterdam MV is located in the Eastern Mediterranean Sea. Previous explorations to this area have discovered gas hydrates just 40 cm below the sea floor, at water depths of 2000 m and seabed temperatures between 12 and 14 degrees C. Gas hydrates formed in such warm environments become notably sensitive if the temperature were to increase any further. Laboratory tests were conducted with multi-component gas hydrates formed in the pore space of the treated sediment. Contrary to what was expected, hydrate dissociation was found to bear a moderate effect on the permeability of the sediment. The measured permeability values with and without hydrates appeared to be of the same order of magnitude. In contrast to permeability, the consolidation behaviour of the host formation was severely affected by the dissociation of the gas hydrate. Consolidation was observed to reach its maximum close to the hydrate stability region and it then collapsed as conditions fell beyond the stability limit. The results indicate that gradual dissociation of the hydrates could bear significant impact on the host deep-sea sediments thus confirming the role of hydrate dissociation as a possible cause of subsea landslides. (C) 2015 Elsevier B.V. All rights reserved.