METHANE

Dr Jekyll or Mr Hyde?

Methane (CH4), the principal component of natural gas, is both a blessing and a curse. On the positive side, it yields 30% more energy than oil, emits less carbon dioxide (CO2) when burned and represents double the oil reserves. On the negative side, methane is a potent greenhouse gas that, when averaged over a century, absorbs 23 times more solar radiation molecule for molecule than CO2.

Analyse du monoxyde de carbone (CO) pour déterminer les rapports isotopiques entre celui-ci et le méthane (CO/CH4) contenu dans des bouteilles d’air en provenance du névé en Arctique. © CNRS Photothèque/Laurence Medard
Analysis of carbon monoxide (CO) to determine the isotopic relations between the CO and methane (CO/ CH4) contained in bottles of air from the Arctic firn. ©CNRS Photothèque/Laurence Medard

In the 1990s, the idea of exploiting me - thane returned to the fore when methane hydrate was discovered, holding out the prospect of new deposits. Methane hydrate (also called methane clathrate or methane ice) is a solid form of water that contains a large amount of methane within its crystal structure (a clathrate hydrate). It is formed mainly through the decomposition of organic matter in a high-pressure, low-temperature environment. There are two types of environment that meet these criteria: the continental slopes at the bottom of the ocean, a few hundred metres under the sea, and permafrost (permanently frozen soil), where the lower pressure is offset by a much lower temperature. A sudden change in these conditions causes a spectacular release of methane: up to 164 cm³ of methane gas for every 1 cm³ of melted ice.

Hunting down methane reserves

To be able to use this wondrous gift of nature on any large scale, we would first need to map the deposits extensively, which is still a long way off. With his HYDRAMED project, Daniel Praeg, oceanographer at Italy's National Institute of Oceanography and Experimental Geophysics (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, OGS), has made a preliminary situation assessment of the Mediterranean. "The plan was to develop theoretical modelling of methane hydrate stability zones and ultimately identify potential sites of interest. This led OGS to discover a methane hydrate deposit in the Nile Fan in 2006. Another site in the Calabrian Arc seems promising because mud volcanoes, which are frequent sources of gas, have been discovered there as the result of collaboration between the HERMES and HYDRAMED projects. Nevertheless, there is still a huge amount of work left to do. It is high time that a comprehensive programme of methane hydrate research and exploration is set up in Europe."

Jérôme Chappellaz, glaciologist at the French Laboratory of Glaciology and Geophysical Environment (Laboratoire de Glaciologie et Géophysique de l'Environnement) and member of the EPICA project team (1), is interested in the influence of methane on our climate. EPICA has taken a 3 270-metre core sample of ice from Antarctica, which takes us back in time 800 000 years. "By analysing the composition of the air bubbles, we can ascertain the exact levels of CO2 and CH4 in the atmosphere over the period. And the results are conclusive," he says, adding, "There has never been such a high methane concentration as there is today. What is more, there is a highly replicable correlation between the variation in CH4 and that of the Earth Radiation Budget." Does this mean that methane hydrate reservoirs should not be exploited at all? Is there a risk that interfering with methane hydrate sites will trigger the sudden release of vast amounts of methane? "Not necessarily," rejoins Jérôme Chappellaz. "There is no evidence to show that there has ever been a massive release of methane into the atmosphere at any time during the 800 000-year period we have examined, in spite of wide variations in pressure and temperature. In addition, living in the murky depths of the oceans are methane-eating bacteria. They form a natural barrier that may play a key role in methane's ability to regulate itself."

The ocean floor and permafrost could contain a total of some 5 000 gigatonnes of methane hydrate - i.e. the same as all the world's oil, natural gas and coal reserves put together. However, as they are dispersed in sediments, they cannot be extracted by conventional drilling, and techniques for exploiting and transporting them have yet to be developed. It is also necessary to clarify and quantify the potential risks to the planet.

Marie-Françoise Lefèvre

  1. See also page 46, 800 000 years under the ice...

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Fint out more

  • Epica
    12 partners - 10 countries (BE-CH-DE-DK-FR-NL-IT-NO-SE-UK)
    www.esf.org

  • Hermes
    50 partners - 15 countries (BE-DE-ES-FR-GR-IE-IT-MA-NL-NO-PT-RO-SE-TR-UK)
    www.
    eu-hermes.net