Wednesday 23 May 2018

Flammable ice: last hope or gravest threat?

London, March 15, 2013

By John Kemp


There is enough gas locked in ice-like crystals buried beneath the permafrost and trapped under the oceans to guarantee the world will not run out of fossil energy for centuries.
This potential energy source will be irrelevant, however, to almost everyone for many decades to come, except perhaps Japan.
For decades, scientists have been trying to figure out whether there is a commercial way to extract the gas from methane hydrates, nicknamed flammable ice.
In an apparent breakthrough, state-owned Japan Oil, Gas and Metals National Corporation (JOGMEC) has extracted natural gas from hydrate accumulations hundreds of meters below the seabed from a drill ship off the east coast of Japan.
JOGMEC estimates its test area contains enough hydrate to cover 11 years worth of gas imports, according to an article published in the New York Times.
Japan is a special case, because the country has almost no hydrocarbon resources of its own and relies almost entirely on energy imports.
The National Institute of Advanced Industrial Science and Technology puts the total hydrate in the waters around Japan at enough to cover nearer 100 years of the country's needs.
For most other countries and companies, developing hydrates comes at the bottom of the list of commercial priorities behind easier and proven forms of fossil energy including conventional and unconventional oil and gas, coal-bed methane, gas-to-liquids and coal-to-liquids technology.
Methane hydrates are the reason the world will never run out of fossil fuels over any reasonable timeframe. But their uncontrolled release has also been identified by climate scientists as one of the biggest long-term dangers for the globe.
"Gas hydrate is a solid crystalline substance composed of water and natural gas (primarily methane) in which water molecules form a cage-like structure around the gas molecules," according to the authors of the 2012 Global Energy Assessment (GEA), a landmark study commissioned by the International Institute for Applied Systems Analysis.
"The cage structure of the hydrate molecule concentrates the component gas so that a single cubic metre of gas hydrate will yield approximately 160 cubic metres of gas and 0.8 cubic metres of water," if it is brought to atmospheric pressure and room temperature (20 degrees Centigrade).
For methane to become trapped in a hydrate structure, temperatures must be moderately cool and pressures moderately high.
"Gas hydrates are widespread in marine sediments beneath the ocean floor and in sediments within and beneath permafrost areas," according to USGS. "There pressure-temperature conditions keep the gas hydrate 'stable', meaning it is intact and gases are contained in its solid form."
Under the oceans, the conditions for hydrate stability are usually found at water depths of more than 150 to 200 metres near the poles and 500 metres towards the equator. The zone of hydrate stability may extend several hundred meters down into the sediments on the sea floor.
Beneath that level, rising temperatures as a result of the greater depth make it impossible for gas to remain trapped. "At some depth beneath the sea floor, the temperature increases to the point where the hydrate is no longer stable," according to the GEA.
The same boundary conditions govern the presence of methane hydrates in and beneath the Arctic permafrost. The methane must be buried far enough north and deep enough to meet the pressure-temperature requirements for hydrates to form, but not so deep that the geothermal gradient makes them unstable.
Methane hydrates are found in most offshore areas around the world, as well as across the Arctic, and contain enormous amounts of energy, but no one really knows how much there is or how much might be technically and economically recoverable.
"The volume of natural gas contained in the world's gas hydrate accumulations greatly exceeds that of known gas reserves, although a substantial proportion of that gas hydrate is in low-grade accumulations that are unlikely to be developed commercially," the GEA concluded last year.
Theoretically, hydrate accumulations could contain between 2,500 and 2.8 million exajoules (EJ) of energy, according to the GEA. An exajoule is equivalent to 1 joule followed by 18 zeroes.
For comparison, global conventional gas resources are put at 12,200 EJ, and unconventional gas resources (tight gas, shale gas, deep gas and coal-bed methane) are estimated at 40,000 EJ, according to the United States Geological Survey (USGS). Conventional and unconventional oil resources are put at around 12,000 and 56,000 EJ, respectively.
In 2010, the International Energy Agency's World Energy Outlook (WEO) estimated that methane hydrates contained almost twice as much energy as all the world's resources of gas, oil and coal combined.
But it is anyone's guess how much could actually be recovered. Ten to 50 percent might be technically recoverable, according to the GEA. The amount that could be economically recoverable might range from 12,000 EJ down to zero.
Hydrates can make up as much as 85 percent of the bulk volume of porous and permeable sands and gravel formations, falling away to less than 10 percent of fine-grained sediments like shales.
Unfortunately, most of the gas hydrate appears to be trapped in fine-grained sediment. "The prospects for commercial development of natural gas from such a highly disseminated resource are very poor without a paradigm shift in technology," the GEA concluded.
Because hydrates are only stable under specific temperature and pressure conditions, the obvious way to disassociate them (converting the hydrate into its separate gas and water components) is either to raise the temperature or lower the pressure.
Other options include injecting the accumulation with an antifreeze chemical such as methanol or ethylene glycol to melt the crystals, or injecting it with carbon dioxide to displace the methane (pushing carbon dioxide into the crystalline lattices and methane out). CO2 injection has the added advantage that it could be part of a carbon capture and storage (CCS) programme.
In onshore tests, Japan's researchers explored using hot water to warm the hydrate. But the offshore test relied on depressurisation; pumping warm water under the seabed would have required an enormous amount of energy and been prohibitively expensive, according to the New York Times.
Climate researchers worry that as global temperatures rise, the hydrates will become unstable, releasing thousands of billions of tonnes of methane into the atmosphere. Methane is 21 times more potent as a greenhouse gas than carbon dioxide.
Mass release of methane hydrates from the ocean floor "appears to have occurred in connection with rapid warming episodes in the Earth's history", according to the Intergovernmental Panel on Climate Change's Third Assessment Report published in 2007.
IPCC estimated 4,000 billion tonnes of methane are locked away in ocean hydrates, with a global warming potential equivalent to 84,000 billion tonnes of carbon dioxide. Annual emissions from burning fossil fuels currently amount to 34 billion tonnes of CO2. Releasing all that methane, or burning it, would have substantial climate consequences.
Environmentalists want the hydrates to remain locked away forever, and they are likely to get their wish for now.
Outside of Japan, where hydrates have the potential to provde energy security, flammable ice will remain an interesting curiosity - a last reserve of fossil fuels if humanity should ever need them in centuries to come when other, far easier hydrocarbon resources are nearing exhaustion. - Reuters
(John Kemp is a Reuters market analyst. The views expressed are his own)

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