Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Uncovering the secrets of ice that burns

02.11.2015

Key properties of methane hydrates found in permafrost and on the continental shelf illuminated

Methane hydrates are a kind of ice that contains methane, and that form at certain depths under the sea or buried in permafrost. They can also form in pipelines that transport oil and gas, leading to clogging. Yet methane hydrates are nearly impossible to study because it is very hard to get samples, and the samples themselves are highly unstable in the laboratory.


Methane hydrates are extremely difficult to study, and could either be an important energy source or a source of methane, a greenhouse gas that is 20 times more potent than CO2. These reasons led a Norwegian, Dutch and Chinese research team to explore the mechanical properties of this poorly understood substance.

Credit: Geir Mogen, NTNU

A team of scientists from Norway, China and the Netherlands has now shown how the size of grains of the molecules that make up the natural structure of methane hydrates determines how they behave if they are loaded with weight or disturbed.

That could have important implications for everything from climate science to their use as a future energy source, said Zhiliang Zhang, a professor at the Norwegian University of Science and Technology and founder of the university's Nanomechanical Lab.

"If we have basic knowledge about the mechanical properties of methane hydrates, we can use this information so that we manage them properly," Zhang said. "How methane hydrates behave can have a big impact on safety, environmental issues and climate change."

Poorly understood and unstable

Methane hydrates have been known since the 1930s, when natural gas companies found that their pipelines were sometimes clogged by a kind of ice composed of water and methane. Methane hydrates were later found in permafrost in the 1960s, and in the oceans, commonly on the edges of the continental shelves, but only at certain ocean pressures and temperatures. They are also thought to be found on other planets, including Mars.

When methane hydrates "melt", they release the methane trapped inside the ice, but because the methane was first trapped under pressure when the hydrate was formed, one cubic metre of solid methane hydrate will release 160 cubic metres of methane gas. That makes them either a potent energy source, or if they melt as the permafrost melts, a potent source of methane, which will act as a greenhouse gas.

But mining methane hydrates as an energy source, an option that is being explored by Japan among others, is technically difficult. Their location on the soft, sediment-loaded edges of the continental shelves makes them difficult to mine, and when they are disturbed, their crystal structure may suddenly dissociate and release the methane trapped inside.

This mechanism has been suggested as one reason why the largest landslide known to humankind, the Storegga Slide, was so destructive. The Storegga Slide took place about 8000 years ago, from an underwater location off the west coast of southern Norway.

The slides - there were three in total¬- sent a wall of water roaring out across the North Sea and Norwegian Sea. The evidence of the passage of the tsunami wave in Scotland that shows the wave reached heights of 3-6 metres in that region. One hypothesis for the slide was that an earthquake caused the methane hydrates in the region to become unstable and to explosively release their gas.

Computer simulations show surprising behaviour

Researchers at NTNU's Nanomechanical Lab and from the university's Department of Chemistry and their collaborators in China and the Netherlands are interested in understanding the relation between molecular structures and the mechanical stability of materials. Methane hydrates, with their ice lattice structure containing trapped molecules of methane, pose an intriguing three-dimensional and practical problem from this perspective.

In a paper published in the 2 November edition of Nature Communications, corresponding author Zhang and his colleagues describe how they used a computer simulation of two types of methane hydrates, monocrystalline hydrates and polycrystalline hydrates, to see what would happen if they were compressed or if pressures on the hydrates were suddenly released.

The researchers built their computer models using common molecular models for ice/water and methane, arranged as either monocrystalline or polycrystalline grains, and simulated the effect of applying forces to the collection of grains.

Maximum capacity found

The simulated hydrate structures were subjected to two different kinds of stress: tensile stress, or the forces they would experience as they were pulled apart, and compressive stress, or the forces they would experience if they were squashed by weight.

The simulations showed that the size of the crystals--what researchers call the grain size--that made up the hydrate structure had a great deal to say in terms of how the structure reacted to both kinds of stresses.

In both tensile and compression stress simulations, the surprising finding was that as the grain size got smaller, the hydrates first got stronger, able to tolerate both compression and tensile stress--but only until they reached a certain grain size. If the researchers conducted simulations on grain sizes smaller than those identified as the turning point, the hydrate actually got weaker.

The maximum capacity of the hydrates appears when the grain size is around 15 to 20 nm. This resembles the behaviour of polycrystalline metals, such as copper. However, this is the first time that researchers have seen this type of behaviour in methane hydrates as a material. The grain size-dependent strength and maximum capacity that the researchers found can be used in predicting and preventing the failure of hydrates in the future.

Instability can be triggered

This unexpected rapid weakening of the crystal structure as the grain size gets smaller has important implications for any work in areas where hydrates are found.

The researchers reported that the dissociation of methane hydrates can be triggered by the ground deformation caused by "earthquakes, storms, sea-level fluctuations or man-made disturbances (including well drilling and gas production from hydrate reservoirs)."

"This has an impact on these big issues," Zhang said. "Here we have taken one step forward, but of course there is a lot more work to be done."

###

Zhang said the researchers plan to continue their collaboration and are currently at work on a center of excellence application to the Research Council of Norway.

Reference: Jianyang Wu, Fulong Ning, Thuat T. Trinh, Signe Kjelstrup, Thijs J.H. Vlugt, Jianying He, Bjørn H. Skallerud and Zhiliang Zhang. Mechanical instability of monocrystalline and polycrystalline methane hydrates. Nature Communications. DOI: 10.1038/NCOMMS9743

Media Contact

Zhiliang Zhang
zhiliang.zhang@ntnu.no
47-930-01979

 @NTNU

http://www.ntnu.edu 

Zhiliang Zhang | EurekAlert!

Further reports about: Methane crystal structure energy source ice that burns structure

More articles from Materials Sciences:

nachricht New material for digital memories of the future
19.10.2017 | Linköping University

nachricht Electrode materials from the microwave oven
19.10.2017 | Technical University of Munich (TUM)

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Electrode materials from the microwave oven

19.10.2017 | Materials Sciences

New material for digital memories of the future

19.10.2017 | Materials Sciences

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>