Gas hydrate strategy reinforced

Sep 15, 2011

Their critics weren't convinced the first time, but Rice University researchers didn't give up on the "ice that burns."

A paper by a Rice team expands upon previous research to locate and quantify the amount of -- a potentially vast source of energy -- that may be trapped under the by analyzing shallow . The paper published this week by the Journal of Geophysical Research- Solid Earth should silence the skeptics, the researchers said.

George Hirasaki and Walter Chapman and Gerald Dickens headed the team.

In 2007, Hirasaki and former graduate student Gaurav Bhatnagar theorized that -- methane that freezes at low temperatures and high pressures -- could be detected via transition zones 10 to 30 meters below the near continental shores; at that level, sulfate (a primary component of seawater) and methane react and consume each other.

As sulfate migrates deeper into the sediment below the seafloor, it decreases in concentration, as evidenced by measurements of pore water (water trapped between sediment particles) from core samples. The depth at which the sulfate in pore water gets completely consumed upon contact with methane rising from below is the sulfate-methane transition (SMT) zone.

In the 2007 paper, Bhatnagar argued the depth of this serves as a proxy for quantifying the amount of gas hydrates that lie beneath; the shallower the SMT, the more likely methane will be found in the form of hydrates in abundance at greater depth.

Though hydrates may be as deep as 500 meters below the seafloor, locating deposits through shallow coring using such proxies should aid selection of deep, expensive sites, the researchers said.

The controversy that followed the publication of the original paper focused on sulfate consumption processes in shallow sediment and whether methane or organic carbon was responsible. Skeptics felt the basis of Bhatnagar's model, which assumes methane is a dominant consumer of pore-water sulfate, was not typical at most sites.

"They believed that particulate organic carbon (primarily from ocean-borne dead matter) was responsible for reducing sulfate," said Sayantan Chatterjee, lead author of the new paper. "According to their assumption, the depth of the SMT, upward methane flux and hydrate occurrence cannot be related. That would nullify all that we have done."

So Chatterjee, a fifth-year graduate student in Hirasaki's lab, set out to prove the theory by bringing more chemical hitchhikers into the mix.

"In addition to methane and sulfate profiles, I added bicarbonate, calcium and carbon isotope profiles of bicarbonate and methane to the model," Chatterjee said. "Those four additional components gave us a far more complete story."

By including a host of additional reactions in their calculations on core samples from the coastline of Oregon and the Gulf of Mexico, "we can give a much stronger argument to say that methane flux from below is responsible for the SMT," said Hirasaki, Rice's A.J. Hartsook Professor of Chemical and Biomolecular Engineering. "The big picture gives more evidence of what's happening, and it weighs toward the methane/sulfate reaction and not the particulate ."

The work is important not only for a natural gas industry eyeing an energy resource estimated to outweigh the world's oil, gas and coal reserves -- as much as 20 trillion tons -- but also for environmental scientists who see methane as the mother of all greenhouse gases, Hirasaki said.

"There's a hypothesis by Dickens that says if the ocean temperature starts changing, the stability of the hydrate changes. And instability of the hydrates can release , a more severe greenhouse gas than carbon dioxide.

"That can create more warming, which then feeds back on itself," Hirasaki said. "It can have a cascade effect, which is an implication for global climate change."

Chatterjee had the chance to discuss his results with his peers in July at the seventh International Conference on Gas Hydrates in Edinburgh, Scotland, where he presented a related paper that focused on the accumulation of hydrates in heterogeneous submarine sediment.

Chatterjee said a number of eminent experts commended him after his talk. "I got a chance to show my recent findings on our 2-D model. This will simplify the search and locate isolated pockets where hydrates have accumulated in deep ocean sediments," he said.

Chatterjee's conference paper was awarded a first prize at the prestigious Society of Petroleum Engineers' Young Professionals meeting and second at the Gulf Coast Regional student paper competition.

Co-authors include Chapman, the William W. Akers Professor of Chemical Engineering; Brandon Dugan, an assistant professor of Earth science; Glen Snyder, a research scientist in Earth science; Dickens, a professor of Earth science, and Bhatnagar, all of Rice.

Explore further: Researchers construct a model of impact for El Nino / La Nina events

More information: www.agu.org/pubs/crossref/2011/2011JB008290.shtml

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User comments : 9

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jmlvu
5 / 5 (3) Sep 15, 2011
So the question now is do we extract the methane and gain energy independence or ban methane extraction to prevent global warming. On a personal level, would you invest in methane to make a buck at the expense of the rest of the world?
GDM
5 / 5 (3) Sep 15, 2011
Great question, but I think we both know what the answer will be, and I'm not sure where I stand on this either. Deep sea/seabed methane extraction will flourish, feeding the world's endless appetite for energy, and we will have to "trust" the deep-water drillers/miners to "keep it clean". Will they do so without government oversight? Doubtful, and unless the regulations have real teeth, the world may see further degradation. If we don't go after the stuff, will it come up naturally as the ocean temperatures increase? Then what?
Eikka
2.5 / 5 (2) Sep 15, 2011
If we don't go after the stuff, will it come up naturally as the ocean temperatures increase? Then what?


We can't possibly hope to remove and burn it fast enough to get rid of it before that happens, especially when burning said methane just releases more CO2 and water into the atmosphere.
GDM
5 / 5 (1) Sep 15, 2011
Hmm Well, water I can cope with, but don't we have methods of dealing with CO2?
holoman
5 / 5 (1) Sep 15, 2011
Check out Advanced Plasma Industries Inc.
GDM
not rated yet Sep 15, 2011
Interesting post Holoman. Let's hope it works out and becomes wildly profitable.
RealScience
5 / 5 (1) Sep 15, 2011
Burning the methane may create CO2, but CO2 is only ~4% as potent a green-house gas as methane.
So if the gas is going to come up anyway (which is far from certain), we are better off burning it.
And if we could capture the CO2 and inject it into old natural gas wells (which held more-mobile natural gas for millions of year, we could get energy and defuse the methane stores at the same time.
We don't have the technology to do this today, but we could in a few decades.
Jimee
not rated yet Sep 17, 2011
Finish destroying the oceans and poisoning us all to last drop. Just right.
RealScience
5 / 5 (1) Sep 17, 2011
Jimee, we aren't that powerful.
We have added ~100 PPM of CO2 to the atmosphere, and might add 100 or 200 PPM more. Cyanobacteria added over 200,000 PPM of highly reactive oxygen to the atmosphere!

The methane clathrates are a ticking time bomb if we don't defuse it. The last time it went off in a big way, in the PETM long before humans, the temperature shot up so far that palm trees grew in the arctic.

That's not to say that we shouldn't worry. The CO2 that we have added has about the weight per area of a light sweater, so it has some impact.
But we don't know whether there would be an ice age coming and that sweater we have inadvertently added to the planet will save us, or whether we are amplifying a warm period and we'll set off the methane clathrate time bomb and cook ourselves unless we defuse it by using the methane.
But worry about us, not the planet or the oceans.
They'll recover in a few hundred thousand year, the blink of an eye on an evolutionary time scale.