Energy

Where do you find them?

Due to the particular conditions required for these compounds to form and remain stable, their presence is limited to three environments: ocean floors, terrains covered by permafrost and the deeper polar ice. The conditions that are more favourable to the formation of methane hydrates are to be found on a large scale beneath the sea beds at depths ranging from 300 to 3,000 – 4,000 m. Above this depth the pressure is not sufficient for the formation of methane hydrates and below it instead, there are optimal pressure and temperature conditions but the organic matter that originates methane is scarce: in other words, at this depth, the ’raw material’ is absent. It is for this reason that methane hydrate deposits seem to concentrate along the continental slope that divides the continental platform from the deep abyssal plains: here great amounts of sediments accumulate that are often rich in organic matter and slide from the continents towards the open sea along the slopes. However, if the temperatures are very low, methane hydrates can form at lower pressures, as, for example, on shallower sea beds (in polar regions) or in the frozen soil covered with permafrost found in vast regions of Alaska and Siberia. The greatest amount of methane hydrates, however, are found in the oceans. They occupy the porous spaces in the sediments for a thickness of several hundreds of metres. At deeper levels within the sediments where the temperature increases due to the geothermal gradient, the methane hydrates dissociate into water and methane gas and, as in the case of normal deposits, they constitute a sort of ‘crust’ that envelops methane in its gaseous state.