Researchers may have found a way to extract large amounts of natural gas from methane hydrates -- ice-like structures that might contain more energy than all the world's coal, oil and conventional natural gas combined.
Massive amounts of frozen natural gas are buried far below the ocean floor and Arctic permafrost, but the compounds are highly unstable when they experience changes in temperature or pressure.
Until now, scientists have struggled to find how to economically extract usable fuel from them.
But Columbia University researchers believe they may have discovered ideal conditions for separating gas from the ice, and they have developed an apparatus to help them do that.
Methane hydrates, also known as "ice that burns," form when natural gas from microbial activity or organic decomposition gets trapped within water molecules at low temperature and high pressure.
Research has begun to find the best way to unlock the energy potential of hydrates under permafrost. The energy source -- which scientists and industry have known about for nearly 200 years but only recently have begun considering as a viable energy alternative -- would be reached using conventional drilling techniques.
But when holes are drilled into the permafrost, the reservoir containing the hydrates is depressurized, which causes the hydrates to become unstable and decompose, said Marco Castaldi, a chemical engineer at Columbia.
"Whenever gas expands, it cools," Castaldi said. "As hydrates decompose, it produces cooling, which re-establishes another equilibrium and creates more hydrates."
To avoid that scenario, scientists have used heat to break down hydrates in a stable manner. Demonstration projects have pumped steam into the reservoir to produce a steady flow of gas. But Castaldi said that method is extremely inefficient.
"Often you're using more energy to make the steam than you're producing," he said. "When you put in more energy than you get out, it doesn't make sense."
And that is where Castaldi's research comes into play.
Castaldi and his colleagues in Columbia's Department of Earth and Environmental Engineering have developed a localized non-steam heat source -- a fuel-burning apparatus that would be placed down the drill hole -- to provide the heat needed to decompose the hydrates and produce a steady stream of methane.
And he said preliminary tests have found their combustion method to be highly efficient: 50 percent or more.
Efficiently maintaining natural gas production could be a key step toward boosting industrial-scale methane production from hydrates, the researchers suggest in a study published in a recent edition of Industrial & Engineering Chemistry Research.
But field testing of a down-hole heating system is likely five to eight years away, Castaldi said, due in large part to the economic crisis and a recent period of tight supply.
The Columbia method has an added benefit, Castaldi said: It can produce fuel in an essentially carbon-neutral way.
The combustion process that heats the reservoir produces carbon dioxide and water -- two ingredients necessary to form another type of hydrate. CO2 hydrates form at a higher temperature than methane hydrates, Castaldi said.
"That's exactly the direction you want," he said. "As things cool down, carbon dioxide forms a hydrate, so it gets sequestered."
He said scientists are still conducting research, but preliminary tests show the method can sequester at least as much carbon as produced in the combustion process.
"It's at least carbon neutral," he said, "but there are indications it could be carbon negative."
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