Methane hydrates, energy of the future or climate time bomb?

Clathrates, also called gas or methane hydrates, are icy structures that contain methane, a fuel but also a powerful greenhouse gas. This source of energy from the cold and abyssal regions could be exploited but it also presents a serious threat to the climatic future of our planet.

Burning ice cream!

Methane hydrates were discovered in the early 19th century and found regularly in the 1970s when drilling for oil.

Clathrates are solid, stable structures that result from the crystallization of a mixture of water and methane. They look like ice cream; as they melt they release both water and methane which can ignite. Indeed, they have the particularity of storing gases in a very concentrated form. The water molecules form a cage around the methane molecules.

Methane hydrates are stable in marine sediments deeper than 300-600 m. But when they are brought to the surface, the decrease in pressure destabilizes the solid structure, the gas is thus released and can burn if ignited, hence the expression "burning ice". also cause the destabilization of hydrates and therefore a release of methane. The area most vulnerable to temperature changes is on the upper continental slope, where sediments containing frozen gases come into contact with warmer ocean waters.

In a study published at the end of July 2020 in Nature Communications, researchers were able to observe off Rio Grande (Brazil), a massive flow of methane made up of hundreds of gas escape points which rise in the water column.

This discovery confirms, for the first time in the southern hemisphere, "a destabilization of gas hydrates consecutive to the warming of the temperature of the ocean in this zone. It is the proof of a thermodynamic imbalance between the edge of the zone of stability observed from seismic data and the rise in temperature of deep waters compatible with a warming of the ocean over several decades.

These sediments form the largest carbon reservoir on Earth and therefore represent a major challenge for the climate.

These gas hydrates form under high pressure and low temperatures. In particular, they could have been generated by the decomposition of bacterial life buried underground.

Gas hydrates: danger for our future?

The exploitation of clathrate reserves has always been avoided for safety reasons: they are flammable and capable of sinking a drilling vessel with the emission of gases which modify the density of the surrounding water.

A colossal source of energy... Difficult to exploit

One cubic meter of clathrates can contain up to 165 cubic meters of methane, a godsend given the current energy crisis, especially since the reserves identified in 2001 are colossal: double the reserves of gas, coal and oil combined. ! That is to say nearly 10,000 billion tonnes of carbon. However, Jacqueline Lecourtier, scientific director of the French Petroleum Institute notes that "Today still, there is terrible uncertainty about the amount of reserves of gas hydrates". At the moment, less than a hundred deposits have been found or strongly suspected along the submarine margins and in the permafrost of the Arctic regions. In the Gulf of Mexico, the clathrates even outcrop and cover the bottom of the sea.

The extraction of clathrates is both dangerous and expensive, but for the first time, a significant technological step has been taken at the Mallik site in the far north of Canada. Indeed, this international research site has was created for the study of Arctic natural gas hydrates in the Mackenzie Delta, northwestern Canada. The high values of gas hydrate saturation, which in some cases were greater than 80% of the pore volume, made it possible to establish that the Mallik gas hydrate field is one of the reservoirs with the highest concentration of hydrates. of gas in the world. In 2002, an expanded consortium of seven international partners and more than 300 scientists and engineers drilled a well to a depth of 1200 m for exploitation and two adjacent wells for scientific observation.

A major risk for the aggravation of the greenhouse effect

The ongoing global warming is notably causing the thawing of permafrost, these soils that are normally permanently frozen. This phenomenon could then release significant quantities of methane with the fusion of gas hydrates. However, methane is a major greenhouse gas 28 times more powerful than carbon dioxide, even if its lifespan in the atmosphere is only ten years against hundreds for CO2.

However, there is 3,000 times more methane contained in clathrates than in the atmosphere. This would then result in a very clear accentuation of the greenhouse effect, as evidenced by certain similar events in the Earth's past which worry scientists. In fact, 55 million years ago, the injection of a colossal mass of methane in the ocean and the atmosphere would have caused the temperature of the bottom of the oceans to increase by about 4°C in 10,000 years, a phenomenon which would also have occurred 12,500 years ago. .

Finally, note that according to climatologist Hervé le Treut, "methane hydrates are not currently integrated into climate models" which provide us with forecasts of the extent of global warming. Additional data that could prove catastrophic if the merger were to become generalized...