Energy bomb or hell bomb? The bet of "burning ice"

Keywords: energy, resources, gas hydrate, methane hydrates, environment, greenhouse effect, runaway

In the bottom of the ocean, billions of cubic meters of gas have been found. What to solve all energy problems. The risk: make global warming totally uncontrollable

Related pages: exploitation of methane hydrates et largest source of primary energy: gas hydrates

It is a kind of strange ice, consisting of an arrangement of water molecules that trap molecules of gas, for example methane, or even propane. Chemists speak of "gas hydrates" or, better, "clathrates", and these products have long been regarded as laboratory curiosities. Fun or dangerous curiosities, because the methane clathrates, apart from their stability conditions (very low temperatures, very high pressures), decompose instantly. As soon as they are extracted from their pressurized fridge, these capricious crystals begin to rage. They disintegrate, explode spontaneously, ignite by releasing their contents of hydrocarbons.

Now, for better or for worse, this playful chemists' game may be conditioning the global future of the planet. Indeed, recently, it has been realized that methane clathrates, these "burning ice", are almost omnipresent, in great quantities, in certain geological layers and particularly in the ocean floor.

The USGS (the US Geological Survey) estimates at tens of millions of billions of cubic meters the amount of methane so trapped in these unstable ice. "That's at least double the amount of all the carbon in fossil fuel, including oil, gas and coal.", says a specialist. And in its last edition "the Journal of the CNRS" is enthusiastic for "this fantastic pactole lying in the bottom of the sea".

Dead organic matter has always decomposed in the sedimentary layers, with fermentation releasing methane. Once the conditions are satisfied (for example, the pressure exerted by a layer of water of 300 meters and a temperature not exceeding 2 at 3 ° C), this methane is immediately sequestered in the form of a solid clathrate. which looks like ordinary ice cream. No wonder then that there is almost everywhere, especially under the continental shelf, and to a lesser depth in the permafrost of the polar regions. Faced with these magical and promising crystals, scientific publications and colloquia have been increasing in recent years. For a long time a little mockery before a fad that they considered worthy of Professor Nimbus, oil companies are now involved in research. Total, Gaz de France and the Institut Français du Pétrole have, for example, partnered with the CNRS to subsidize a laboratory called "processes in granular media", hosted by the Ecole des Mines de Saint-Etienne. This is to experiment a process of extraction of methane clathrates by hot water injections into the deep layers, and its recovery in gaseous form.

At the same time, numerous international scientific collaborations are organized to inventory the most promising deposits. Thus, next September, Marie-Madeleine Blanc-Valleron (CNRS and National Museum of Natural History in Paris) will embark aboard an American ship to analyze boreholes off Vancouver, where a phenomenal accumulation of Methane hydrates at the border of two tectonic plates. The French researcher is preparing to "spend ten to twelve hours a day under the microscope, whatever the state of the sea", as part of a "very special international mission": it is not at the moment to identify a particular bed of methane, but to study the mechanism of gas accumulation in sediments, in order to establish a general geological model that will allow to know where to look for them in the future.

For its part, the European Commission is financing the Hydratech program, which is developing techniques for detecting methane clathrates on the continental shelves of the Old Continent. Already, apparently promising areas have been identified - "in the Black Sea, in the eastern Mediterranean, in the Gulf of Cadiz and in the Norwegian Sea", reveals "the Journal of the CNRS".

It is certain, the day when we will be able to draw from this unexpected methane, the specter of the energy shortage will be removed for a long time. Even if we only knew how to recover a very small fraction, the accessible quantities would be phenomenal: properly heated and pumped, a single cubic meter of clathrate gives not less than 164 cubic meters of natural gas. But playing with this ice cream is also playing with fire. Firstly because it is in any case a fossil fuel, the combustion of which contributes to the unfortunate greenhouse effect. But especially because any unfortunate destabilization of this methane, frozen since the dawn of time, could lead to the massive degassing of huge deposits.

One can imagine myriads of cubic meters of this gaseous hydrocarbon escaping with a single blow from the seabed. The bubbles shake the ocean before reaching the atmosphere to accelerate global warming - because methane is also characterized by a very effective greenhouse effect (21 times more than CO2).

Then this global warming accelerates in its turn the rise in temperature of the oceans, and thus causing in cascade the degassing of other deposits of clathrates: an infernal spiral which could inspire a disaster film ...

Such a scenario should not be dismissed lightly. All the less since - without having reached the paroxysm of widespread conflagration until now - it has really occurred in nature, and has been for a long time. Thus, the current global warming inevitably results in the degassing of previously frozen methane, in some polar regions where the melting of permafrost brings the clathrates to the limit of their stability. Experts speak of the "horizon of hydrates" to designate this limit - a combination of temperature and pressure beyond which methane enters the gaseous state, escaping into the atmosphere without being recovered and without going through a Gaz factory.

In theory, no doubt: even if the phenomenon remains limited, the methane released by the warming contributes, through a strengthening of the greenhouse effect, to the acceleration of the warming. And so on. In the past massive outgassing has occurred, resulting in climatic disasters. "Sometimes, nature breaks the equilibrium between the gas phase and the solid phase of the underwater methane," says Pierre Henry, CNRS. Traces of it remain, still visible thousands of years later, like the gigantic "mud volcanoes" that line certain ocean floors, due to sudden local escapades of methane - it is the "champagne effect", say the geologists. A team from the University of Michigan could even establish a link between a titanic release of gas occurring in the Atlantic 55 million years ago and concomitant global warming: an average rise from 4 to 6 ° C. The climate of the planet had taken 200000 years to recover.

Let's hope we're not messing it up for so long.