Economy, ecology, technologies and society Methane hydrates

Energy bonanza or infernal bomb? The "burning ice" bet

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

Billions of cubic meters of gas have been found at the bottom of the oceans. Enough to solve all energy problems. The risk: making global warming totally out of control

Related Pages: Mining of Methane Hydrates and the Largest Primary Energy Source: Gas Hydrates

It is a kind of strange ice, made up of an arrangement of water molecules which trap gas molecules, for example methane, or even propane. Chemists speak of "gas hydrates" or, better, "clathrates", and these products have long been considered laboratory curiosities. Amusing or dangerous curiosities, because methane clathrates, outside of their stability conditions (very low temperatures, very high pressures), decompose instantaneously. As soon as they are extracted from their pressurized fridge, these capricious crystals begin to fulminate. They disintegrate, explode spontaneously, ignite, releasing their hydrocarbon content.

However, for better or for worse, this joke of facetious chemists may condition the global future of the planet. Indeed, recently, it has been realized that methane clathrates, these "burning ices", are almost omnipresent, in tremendous quantities, in certain geological layers and in particular at the bottom of the oceans.

The USGS (the American Geological Survey) estimates the amount of methane trapped in this unstable ice at several tens of millions of billions of cubic meters . "This represents at least double all the carbon contained in all fossil energy deposits, including oil, gas and coal," says a specialist. And in its latest edition "the Journal du CNRS" is enthusiastic about "this fantastic jackpot that lies at the bottom of the sea".

Dead organic matter has always decomposed in the sedimentary layers, their fermentation releasing methane. As soon as the conditions are met (for example, the pressure exerted by a layer of water 300 meters high and a temperature not exceeding 2 to 3°C), this methane is immediately sequestered in the form of a solid clathrate that looks like regular ice cream. It is therefore not surprising that they are everywhere or almost, in particular under the continental shelves, and at less depth in the permafrost of the polar regions. Faced with these magical and promising crystals, scientific publications and conferences have multiplied in recent years. Having long remained a bit jesting in front of a whim that they deemed worthy of Professor Nimbus, the oil companies are now taking part in research. Total, Gaz de France and the French Petroleum Institute have, for example, joined forces with the CNRS to subsidize a so-called “processes in granular medium” laboratory, hosted by the Ecole des Mines de Saint-Etienne. This is to experiment with a process for extracting methane from clathrates by injecting hot water into the deep layers, and recovering it in gaseous form.

At the same time, many international scientific collaborations are being organized to inventory the most promising deposits. Thus, next September, Marie-Madeleine Blanc-Valleron (CNRS and Muséum national d'Histoire naturelle de Paris) will embark on board an American ship to analyze drilling carried out off Vancouver, where we suspect a phenomenal accumulation of hydrates at the boundary 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", within the framework of a "very special international mission": it is not a question for the moment to identify a particular deposit of methane, but to study the mechanism of accumulation of the gas in the sediments, in order to establish a general geological model which will make it possible to know where to look for them in the future.

For its part, the European Commission finances the Hydratech program, which develops techniques for detecting methane clathrates on the continental shelves of the Old Continent. Already, apparently promising areas have been spotted – “in the Black Sea, in the eastern Mediterranean, in the Gulf of Cadiz and in the Norwegian Sea”, reveals “le Journal du CNRS”.

It is certain, the day when we will be able to go and draw this unexpected methane cheaply, the specter of the energy shortage will go away for a long time. Even if we only knew how to recover a very small fraction, the accessible quantities would be phenomenal: suitably heated and pumped, a single cubic meter of clathrate yields no less than 164 cubic meters of natural gas. But playing with this ice is also playing with fire. Firstly because it is a fossil fuel anyway, the combustion of which contributes to the unfortunate greenhouse effect. But above all because any unfortunate destabilization of this methane, frozen since the dawn of time, could lead to the massive degassing of huge deposits.

One imagines myriads of cubic meters of this gaseous hydrocarbon escaping all at once from the seabed. Bubbles shaking the ocean before reaching the atmosphere to accelerate global warming there – because methane is also characterized by a very effective greenhouse effect (21 times more than CO2).

Then this global warming in turn accelerating the rise in temperature of the oceans, and therefore causing the cascading degassing of other clathrate deposits: an infernal spiral that could inspire a disaster film...

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Such a scenario should not be dismissed lightly. Especially since – without having hitherto reached the paroxysm of generalized conflagration – it really occurs in nature, and has done so for a long time. Thus, the current global warming inevitably translates into the degassing of methane that was frozen until now, in certain polar regions where the melting of the permafrost brings the clathrates to the limit of their stability. Specialists speak of the "hydrate horizon" to designate this limit - a combination of temperature and pressure beyond which the methane enters the gaseous state, escaping into the atmosphere without being recovered and without passing through a Gaz factory.

In theory, there is no doubt: even if the phenomenon remains limited, the methane released by global warming contributes, via a reinforcement of the greenhouse effect, to the acceleration of global warming. And so on. In the past, massive degassings have occurred, leading to climatic disasters. "Sometimes, nature itself breaks the balance between the gaseous phase and the solid phase of underwater methane", observes Pierre Henry, of the CNRS. Traces of it remain, still visible thousands of years later, such as the gigantic “mud volcanoes” that line certain ocean floors, due to sudden local escapes of methane – this is the “champagne effect”, say the geologists. A team from the University of Michigan was even able to establish a link between a titanic release of gas that occurred in the Atlantic 55 million years ago and the concomitant global warming: an average rise of 4 to 6°C. The planet's climate had taken 200,000 years to recover.

Hopefully we're not messing it up for that long.