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Up to 40% of Gulf Oil Spill Was Potent Methane Gas, Research Shows

The findings underscore how little is understood about the behavior of gases in oceans, as countries launch the first gas hydrate drilling programs

By Lisa Song

Mar 3, 2011
An outcrop of methane hydrates, underwater.

Several countries, including the U.S., are conducting hydrate test drilling programs for potential energy use.

The ocean floor — and the Gulf Coast region in particular — is littered with natural methane seeps where gases bubble up through the water column. As the bubbles rise, they develop hydrate "skins" that protect the methane from dissolving, which helps the methane to reach the ocean surface.

In the case of the Macondo well, the methane became trapped in a deep-sea layer about 3,000 to 3,600 feet down, where scientists reported a "snowstorm" of methane hydrate particles. The gas layer also contained "significant" amounts of oil, said Leifer. But it remains a mystery why bubbles disappeared and methane hydrate particles formed at that particular depth.

"I believe that something happened outside of anything we scientists understand," he said.

New Findings Stir Controversy

The researchers' findings have stirred up much debate in the academic world. For one thing, their calculations of the total gas discharge of 260,000 to 520,000 tons are much higher than the estimates of other scientists.

In early January, a research team led by John Kessler, an oceanographer from Texas A&M University, and David Valentine, a UC Santa Barbara geochemist, that the BP spill released 190,000 to 260,000 tons of gas.

More contentious, however, is their assertion that microbes have already consumed most of the gas.

During research cruise trips between August and October 2010, Kessler and Valentine took hundreds of water samples from the northern Gulf of Mexico and found no evidence of the BP gas.

A counter-argument comes from Joye, who said that the gaseous layer, or plume, has simply moved elsewhere. The plume's progress was poorly tracked from June to August, and the gases would have dispersed to different parts of the ocean.

Valentine disagreed.

"It's quite clear that we identified the majority of the plume," he told SolveClimate News, adding that instead of methane, they found zones of low oxygen and a large "community" of methanotrophs, or methane-eating microbes.

There were far more methanotrophs than what was present in May and June, he said. "So basically the methanotrophs are there now, and they're dying off since they [consumed their food source]."

Using information on ocean currents, Kessler and Valentine also found other indications of the plume — namely, the dispersants and fluorescence from the oil.

Both were mixed with the gases in the plume, and all would have moved with the ocean currents, said Valentine.

Joye argues that circulation in the deep Gulf is complex. "It's not flowing like a river. It breaks off and you get little eddies … [The Gulf] is a huge body of water." Since the methane wasn't routinely measured between late June and early August, "we basically lost track of [the gas]."

Countries Begin Drilling for Gas Hydrates

The scientific debate is expected to continue through future peer-reviewed works, and such controversy underscores how little is understood about the behavior of gases in deep-ocean systems.

The need for basic research echoes growing interest in the energy sector.

The U.S. has several projects aimed at developing gas hydrate resources. BP is drilling a test well on the north slope of Alaska to study the occurrence of hydrates and may start production testing within the next two years. In the Gulf of Mexico, Chevron is drilling to document hydrate abundance. Both projects are conducted in partnership with the Department of Energy.

Internationally, Japan, India and South Korea are sinking vast resources into hydrate drilling programs. Japan hopes to start commercial extraction by 2018.

But drilling for hydrates is not without dangers.

A major concern is that hydrates are very efficient at storing gas. One cubic foot of solid gas hydrate expands into 160 to 180 cubic feet of free gas at the surface. That sudden expansion could lead to explosions or harm drilling equipment. The Japanese report they've developed a drilling method that slowly decompresses the hydrates.

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