x Abu Dhabi, UAESaturday 22 July 2017

Still in its cage: the wonder fuel of the future

Methane found in frozen water may be either the wonder fuel of the future, or another potent greenhouse gas.

Can methane hydrate solve the world's energy crisis? Courtesy of Japan Oil Gas and Metals National Corporation / Bloomberg News
Can methane hydrate solve the world's energy crisis? Courtesy of Japan Oil Gas and Metals National Corporation / Bloomberg News

A team from the US and Japan has tapped into vast quantities of methane trapped in frozen water. After an experiment in Alaska, the team might have found a neat solution to the world's energy crisis. But considerable research is still needed, writes Robert Matthews

It looks like a conjuring trick: chunks of dripping-wet, icy stuff somehow emitting flames. Yet this bizarre sight may hold the key to the even more spectacular trick of making the global energy crisis vanish.

The white substance is methane hydrate, formed from the prime constituent of natural gas trapped in a cage of frozen water. Thought to lie in vast quantities in permafrost and off the coast of many countries, it was long seen as a curiosity by scientists, and a nuisance by deep sea drilling crews.

But now the success of the first tentative steps towards exploitation is prompting talk of methane hydrate as a potential rival to mainstream energy sources.

It also marks the latest twist in our relationship with methane, which has swung from being seen as a climate-change threat to a cheap, clean wonder-fuel.

As the simplest of all hydrocarbons, methane is the most efficient fossil fuel for generating power, producing more heat and less carbon dioxide pro rata than any of its rivals.

Small wonder, then, that the discovery of vast reserves of methane trapped in sedimentary rock - "shale gas" - around the world has sparked so much interest.

Now there is mounting excitement over the even bigger reserves of methane trapped in "cages" of water in permafrost and deep beneath the sea.

Quite where this methane comes from is not entirely clear. Conventional natural gas is thought to be a genuine fossil fuel - the product of the geological crushing and heating of ancient plant remains over millennia. But scientists are less sure of the origins of the methane trapped in hydrates.

Some of it may be the result of bacterial action, but most appears to be the product of organisms known as archaea - a form of microbial life distinct from bacteria and whose very existence was disputed until recently.

Yet another potential source is the complex of chemical reactions between rocks and minerals found on the ocean bed.

Whatever its origin, any methane formed under conditions of high pressure and low temperatures - such as in permafrost or the deep ocean - can end up crammed into cage-like arrangements of water molecules, forming methane hydrate.

The packing is pretty efficient: a cubic metre of the hydrate contains more than 160 cubic metres of methane.

While the existence of this strange chemical combination was first noted more than 200 years ago, it was long regarded as a curiosity that formed only under very special conditions.

But in the 1930s, it became all too clear that these conditions could be found deep under the sea. Deep sea drilling rigs encountered the strange white stuff at depths of more than 1,000 metres, where the right combination of high pressure and low temperatures for methane hydrate formation are found.

Pipelines can easily become clogged when the stuff forms around methane leaks. Changes in pressure or temperature once it has been formed can also trigger the release of the caged methane, with potentially explosive results.

Despite the challenges, the prospect of exploiting this potential energy source - estimated to be greater than all the rest of the world's fossil fuels combined - is alluring. And now a first step to doing so has been taken in the icy wastelands of Alaska.

Bordering the Arctic Ocean, Alaska's North Slope has huge reserves of relatively accessible methane hydrate trapped in permafrost. A team from the United States and Japan has just completed a month-long experiment aimed at extracting the methane using potentially commercially viable technology.

Engineers injected carbon dioxide and nitrogen into the hydrate formations, and then lowered the pressure in the drill well. Sure enough, the icy cages of frozen water swung open, releasing their methane for collection.

According to the team, further tests are planned to build on the success of the experiment, but it will be years before the reserves come online.

It will take much longer still to solve the challenges of accessing the vast fields beneath the sea.

Not everyone is in a hurry. Environmentalists, already up in arms over the extraction of shale gas, are becoming increasingly worried about the global "dash for gas".

They point out that while methane produces less carbon dioxide than any other fossil fuel when it is burnt, it is still not zero carbon dioxide.

Unless we stop using these fuels completely, they argue, the result will be ever more carbon dioxide in the atmosphere, and an ever warmer planet.

But the Alaska study points to a neat twist in the tale. In the tests, carbon dioxide was used to replace the methane trapped in icy cages. This raises the possibility of a chemical "prisoner exchange" in which we swap the carbon dioxide we don't want for the methane we do - thus tackling both global warming and the energy crisis in one go.

Too good to be true? Quite possibly: it may never be economically viable - and it would certainly have to be done carefully. As deep sea drillers have already shown, disturbing methane hydrate can lead to explosive releases of the gas.

But environmentally, the consequences of a major shift could be far worse. Methane is known to be a much more potent greenhouse gas that carbon dioxide, and a massive release of it due to, say, extraction-triggered undersea avalanches could produce wholesale climate change.

This isn't some imaginary scenario: scientists have evidence that past releases of undersea methane, perhaps due to an earthquake, have warmed the planet dramatically, ending past ice ages. Some have even claimed a link between releases of the gas, climate change and mass extinctions of life.

Research is just beginning into how to perform the daring double-headed trick of swapping peril for promise. Let us hope scientists can pull it off without making the human race vanish in a vast puff of gas.

 

Robert Matthews is Visiting Reader in Science at Aston University, Birmingham, England

 

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