After discussing polymetallic nodules, there is an even more promising mining resource in the abyss: methane hydrates. More promising because they are a major source of hydrocarbons.

I. What are methane hydrates?

A. Composition

Methane hydrates are a solid compound, a crystallization of water molecules trapping methane (CH4) molecules under certain temperature and pressure conditions.

The methane (CH4) molecules are released at room temperature. Even if methane remains the main gas present in hydrates, other gases can be discovered such as carbon dioxide (CO2), hydrogen sulfide, etc.). There are called “gas hydrates”.

Methane (CH4) is a gas that can come from two sources:

  • It is a biogenic gas if it is produced from organic animal or plant matter by bacteria living in an anaerobic environment (without oxygen)
  • It is a thermogenic gas if it is derived from organic matter preserved from bacterial degradation by pressure and temperature when buried in the ground.

It is an unconventionnal gas as tight gas/tight oil, coalbed methane and shale gas. There are called “unconventional” because the extraction process is costly and more complex than the extraction of crude oil or natural gas (even if, the production of shale gas is more common these past years).

Methane hydrates are lodged in the layer called permafrost, which is the layer of permanently frozen ground on the ocean floor.

B. Deposits

The first two countries to embark on the first projects were Russia (since the 1960s, large quantities have been trapped in the permafrost) and Japan (since 2013, the country has been producing and marketing gas from methane hydrates).

Reserves are estimated at between 3 million and 10 million billion m3 , although the exact and profitable share exploitable is still subject to debate.

C. Seabed mining processes

There are 3 processes that could work to mine methane hydrates :

1. Depressurization

The hydrate layer at the base is drilled into, and the decrease in pressure allows the methane to be released and dissociate. This is the most promising method.

2. The use of an inhibitor

An additive such as methanol or glycol is injected to change the stability conditions of the methane hydrate. This is the most expensive method and the most risky. Large quantities of additives released into the ocean would likely have consequences for the surrounding biodiversity.

3. Thermal steam or hot water injection

Increasing the temperature will result in the dissociation of the water and methane molecules. This process is more expensive than depressurisation for the same volume of gas.

II. What about environment ?

Two major risks could affect the environment following the extraction of methane hydrates: on the one hand, a local risk, as hydrates stabilize submarine slopes, drilling could therefore cause a geohazard as submarine landslides (increasing the risk of tsunamis). On the other hand, there is a global risk, since the accidental release of a large quantity of methane would have a very significant greenhouse effect (one tonne of methane has a global warming potential up to 30 times higher than CO2).

In 2013 the European Commission launched the MIDAS (Managing Impacts of Deep-seA reSource exploitation) 3-year research program, a European consortium of scientists, NGOs (Nongovernmental organizations), and SMEs (Society for Mining, Metallurgy, and Exploration) in charge of studying the environmental impacts of mineral and energy extraction from the sea bed.

For methane hydrates, there 2 chosen zones: the Black Sea and the Norwegian and Svalbard continental margins.

According to the MIDAS’s website, the programm’s purpose was to identify :

  • “the physical destruction of the seabed by mining, creation of mine tailings and the potential for catastrophic slope failures from methane hydrate exploitation;
  • the potential effects of particle-laden plumes in the water column,
  • and the possible toxic chemicals that might be released by the mining process and their effect on deep-sea ecosystems.”

After assessing scientific approaches to observe consequences on the seabed, the report concludes that, for now, further measures are required.


– Connaissance des énergies, Les hydrates de méthane:

– Projet MIDAS:

– MIDAS, Research Highlights:

A propos de Eva-Luce BAILLY