Formation of gas hydrates in a permeable medium

Abstract

Gas migrating upwards in deep sea sediments can form a thin zone of solid gas hydrates, which can act as a seal below which free gas is trapped. The acoustical contrast between the water-bearing sediments above this seal and the gas-containing sediments below it could cause seismic reflectors with a negative polarity running subparallel to the sea floor. The gas hydrate seal itself would be too thin to be resolved by seismic methods. To clarify whether gas hydrates could form such thin seals that are still effective, the formation of gas hydrates in a sediment has been simulated in laboratory experiments. An effective seal was formed from propane and water within 15 minutes in a coarse sand pack. This seal when 5 cm thick, could withstand a pressure difference of 2.4 bar. This finding supports the above model.