Sunday, April 28, 2013

Fire Ice or Methane energy source?

"Demystifying Fire Ice: Methane Hydrates, Explained"

In Japan, energy companies are targeting pockets of methane hydrate, colloquially called "fire ice," deep under the sea.


Jon M. Chang

March 19th, 2013

Popular Mechanics

The Japan Oil, Gas, and National Metals Corporation (JOGMEC) announced last week that it had successfully extracted fuel from a deep-sea bed of methane hydrate located off the coast of Shikoku Island. This particular deposit of methane hydrate (also known as fire ice) contains an estimated 40 trillion cubic feet of natural gas, equal to 11 years' worth of gas consumption in Japan. The country, as the world's No. 1 importer of natural gas and a country still recovering from the Fukushima nuclear disaster, could see this natural gas as a major part of its energy consumption over the next decade.

But what exactly is fire ice?

Methane hydrate's exotic nickname is a reference to the compound's chemical structure: molecules of methane gas trapped within a cage of solid water molecules. The cage does not form in everyday conditions. To make the hydrate, both the methane and water need to be in an environment with the right temperature and pressure.

Timothy Collett, a research geologist at the United States Geological Survey (USGS), says that these conditions exist naturally either buried under Arctic soil or, as with the Shikoku deposit, buried in a marine basin. When taken outside of these conditions, methane hydrate doesn't last for long. "It would dissociate within minutes, maybe an hour," he says.

Methane hydrate hasn't always been seen as a fuel source. In the 1940s, it was a nuisance: Engineers discovered the material clogging up the natural gas pipelines. They realized that gas was mixing with water and forming large chunks of methane hydrate, which caused blockages. Even today, gas pipeline companies spend a significant portion of their operational budgets—as high as 10 percent, according to Collett—to prevent these blockages. It wasn't until the 1960s that scientists discovered that methane hydrate exists in nature, and into the 1980s that they saw it as a potential source of fuel.

Scouting for usable methane hydrate deposits is still a work in progress. For now, the process mimics similar work in finding oil or gas. Collecting seismic data has revealed some methane hydrate deposits. "They're solid, so they have a high acoustic velocity," Collett says, "but the signal appears different than one propagated through regular soil." A current estimate suggests that there is approximately 100,000 trillion cubic feet of methane gas locked in hydrates, but that only about 10 percent of that is commercially viable to extract—the rest is scattered in small pockets.

Another stumbling block in making methane hydrate usable is figuring how to acquire the gas from the solid. Because the methane hydrate solid is stable only within a set range of temperatures and pressures, altering those conditions would liberate the gas from its water cage, letting people extract it. Companies are experimenting with a depressurization method, which works by drilling a wellbore into the deposit itself and pumping out all the excess fluid. With less surrounding fluid, the pressure drops, prompting the methane hydrate to dissociate. The depressurization method worked at the smaller Mallik Gas Hydrate Research Well in northern Canada, as well as at the large one beneath Japanese waters. Heating the deposits could also release the gas but is too energy-intensive to be worthwhile.

But what if the earth released the gas as a result of heating up? Not only energy companies but also scientists studying climate change have a major interest in methane hydrates. Methane is a greenhouse gas, a far more powerful one than carbon dioxide, and some scientists fear the warming of the earth could destabilize hydrates to the point that they release methane into the atmosphere, further worsening global warming. Ideas such as the clathrate gun hypothesis suggest that methane hydrate dissociation is linked to prehistoric global warming.

However, according to a Nature Education paper published by the USGS, only about 5 percent of the world's methane hydrate deposits would spontaneously release the gas, even if global temperatures continue rising over the next millennium. In addition, bacteria in the nearby soil can consume and oxidize the methane so that only a minute fraction (as low as 10 percent of the dissociated methane) ever reaches the atmosphere.

There's another potential method for extracting methane that might actually help to combat climate change. Research at the Ignik-Sikumi well, located off Alaska's North Slope, has shown that carbon dioxide can replace methane within the ice cage. Once the carbon dioxide is locked in, the water cage binds even tighter, leaving no room for the methane to reenter. Collett says this way of extracting methane gas for fuel could one day double as a way to sequester carbon CO2.

It will still be years before methane hydrates become a commercial source of fuel, and not only because the technology is still young. Even with the infrastructure in place, a methane hydrate well can take years before it regularly produces fuel. Depressurizing methane hydrate doesn't happen all at once but slowly propagates through the entire deposit.

Collett sees gas hydrates as a science project at this stage, saying that it's still in the early stages of research and development. JOGMEC itself acknowledges that it still has many questions to answer. In a translated statement, officials say that the current project off Shikoku will also acquire data about the well's impact on the marine environment. "It's one of those things that has a great potential," Collett says, "but it's still only a potential."

Methane clathrate [Wikipedia]

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