Finding the Ice that Burns

September 16th, 2011
in econ_news

ice-that-burns Econintersect: There is an elusive source of energy that has intrigued energy explorers and strategists for years. It is known as methane hydrate, a complex solid structure of methane and water that forms at low temperatures and high pressures, and shown burning in a technician's hands. Theories abound that the material could be plentiful at depths of several hundred meters or more beneath the ocean floors. There are also possible sources of the fuel deep below the arctic permafrost and beneath the Antarctic continent. According to Wikipedia, methane hydrates (also called methane clathrate) are conservatively estimated to total twice the amount of carbon in all known fossil fuels of Earth.

Follow up:

Researchers at Rice University have published a paper in the Journal of Geophysical Research Solid Earth that demonstrates a technique of using shallow core samples to detect the presence of much deeper situated methane hydrate. This technique enables relatively inexpensive shallow sampling to determine the most likely places to undertake deep drilling for the methane.

From R&D Magazine:

In 2007, Hirasaki and former graduate student Gaurav Bhatnagar theorized that gas hydrates—methane that freezes at low temperatures and high pressures—could be detected via transition zones 10 to 30 m below the seafloor 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 transition zone 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.

It turned out that the hypothesis of the 2007 paper was challenged on the basis that organic sediments could also react with the sulfur and such reactions would be indistinguishable for those occurring with seepage of methane. That led to further research and the 2011 paper.

Again from R&D Magazine:

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," says 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 says. "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," says 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 organic carbon."

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 says.

"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 methane, a more severe greenhouse gas than carbon dioxide.

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

Sources: Wikipedia, Journal of Geophysical Research Solid Earth and R&D Magazine

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