This strange substance could provide vast quantities of natural gas; no surface targets, where warming could release methane into atmosphere

 

BY ALAN BAILEY FOR GREENING OF OIL 

Methane hydrate, sometimes referred to as ice that burns, is a strange lemon-sorbet-looking material that exists naturally in huge quantities in a number of places around the world, and locks up vast quantities of methane, the primary component of natural gas. Scientists have estimated that there may be somewhere in excess of 1,000 billion tons of methane hydrate in existence worldwide, a figure thought comparable to the total remaining amount of fossil fuels such as coal, oil and more conventional forms of natural gas.

One of a class of substances referred to by the somewhat arcane scientific name of “clathrates,” methane hydrate consists of methane (which is a gas at normal temperatures and pressures) trapped in a solid lattice of water molecules, somewhat like ice. The material is only stable within a certain range of pressures and temperatures—shift the temperature or pressure outside that stability range and methane hydrate will break down, releasing a volume of methane gas amounting to about 164 times the volume of the original hydrate.

The sensitivity of the material to pressure and temperature means that naturally occurring methane hydrate tends to exist only in certain specific situations, such as in cold sediments under the coastal margins of the world’s oceans, or deep under the frozen tundra of Arctic lands. Essentially, the hydrates have formed where methane bubbling from the decomposition of buried organic material has become trapped in wet sediments, where the pressures and temperatures are conducive to hydrate formation. 

A possible energy source

But would it be possible to extract methane from the hydrate deposits as a new and prolific source of natural gas, a relatively clean burning fuel thought by some to be a potential transition fuel to a more renewable energy future?

“Right now there are a number of countries that have research programs dedicated to finding if hydrates can be an (energy) resource,” Ray Boswell, technology manager for gas hydrates with the U.S. Department of Energy’s National Energy Technology Laboratory, told Greening of Oil on April 21. The United States, Japan, Canada and Korea have been leading the research, with China also rapidly becoming involved, Boswell said. India is also talking about conducting methane hydrate exploration, he said.

But for methane hydrate to become a viable energy source there will need to be technically feasible ways of extracting methane from the hydrate in commercial quantities. In addition, the cost of finding the hydrate deposits and then developing them and shipping the produced gas needs to be economically feasible—if natural gas from methane hydrate is excessively expensive, people will use other energy sources.

And the often remote locations in which methane hydrate occurs render the technical and economic issues involved in methane hydrate production especially challenging. 

North Slope research

In the United States, much research attention has focused on the North Slope of Alaska where extensive deposits of methane hydrate are known to exist in sands buried around 2,000 feet deep, below the base of the permafrost, the layer of permanently frozen ground under the tundra. The proximity of these hydrate deposits to the existing infrastructure associated with North Slope oil fields such as Prudhoe Bay would significantly lower the economic barriers to hydrate production in the area. In fact, people view the North Slope hydrates as the “low hanging fruits” of possible methane hydrate development.

So, could natural gas be produced from these relatively accessible deposits for delivery to market through a future North Slope gas line? A multiyear joint government, industry and university project involving North Slope oil producer BP and funded in part by DOE has been researching methane hydrate deposits in the central North Slope, refining ways of locating the deposits using seismic data and assessing ways in which the deposits might be developed. In 2007 BP successfully drilled a test well into one of the deposits, enabling the research team to retrieve hydrate samples for laboratory testing and allowing some brief testing of the methane production characteristics of the in-situ methane hydrate material.

In a parallel DOE supported project, ConocoPhillips, another North Slope oil producer, has done laboratory tests on synthetic methane hydrate, to assess the possibility of producing methane from the hydrate by injecting carbon dioxide into the hydrate deposits—the carbon dioxide would simply replace the methane in the lattice of water molecules, thus providing the added benefit of disposing of waste carbon dioxide from oilfield operations. 

Methane hydrate in the Gulf of Mexico

And another joint government, industry and university project, this time located in the Gulf of Mexico and led by oil company Chevron, has most recently focused on refining ways of locating methane hydrate deposits in subsea sediments, and in evaluating how much hydrate resource might lie in sands under the Gulf. With a well-developed oil and gas infrastructure, the Gulf of Mexico is another potential site for future methane hydrate production.

The Gulf of Mexico project, with DOE funding, drilled seven wells in 2009 to test methane hydrate prospects located primarily from seismic data and geologic knowledge, Boswell said. The wells found hydrate deposits in similar concentrations to what people know to exist in northern Alaska, he said. And although these initial results do not clarify how much methane hydrate exists under the Gulf of Mexico, the results do prove the existence of at least some deposits, a concept that had faced skepticism from some people, Boswell said.

Elsewhere in the world, the Japanese have been spearheading methane hydrate research, while Korea plans to drill some wells in June, to evaluate some of its offshore methane hydrate prospects. 

Japanese offshore interest

Interest in Japan is in developing known offshore methane hydrate deposits in the Eastern Nankai Trough, off the Pacific Coast of Honshu Island. And the Japanese conducted some offshore drilling in 1999 and 2004, demonstrating the existence of methane hydrate deposits in the target region, Boswell said. However, given the high cost of marine drilling, the Japanese elected to do some initial testing onshore by collaborating with Canada and other nations to drill a methane hydrate test well on a Canadian Arctic island.

The Canadian well focused on what seems an especially promising means of producing natural gas from hydrate: Simply pull free gas trapped in the sand adjacent to the hydrate, to reduce the gas pressure in the sand and hence cause the solid hydrate to disassociate. And in 2008 the researchers successfully demonstrated the use of this technique to produce gas from the Canadian well over a period of six days.

Encouraged by the results from the North Slope and Canadian wells, in October 2008 the U.S. Geological Survey deemed it to be technically feasible to recover natural gas from some methane hydrate deposits and the agency came up with the first ever methane hydrate resource assessment, saying that it would be possible from a technical, if not economic, perspective to recover 85 trillion cubic feet of natural gas from methane hydrate under Alaska’s North Slope. 

Production tests come next

But no one has yet demonstrated sustained industrial-scale production of natural gas from methane hydrate, let alone shown that this production can be achieved within feasible cost parameters. And, so, all of the various research projects are now essentially headed in the same direction: tests of more sustained natural gas production to pin down the likely costs and production characteristics of a commercial methane hydrate operation. People need to find out, for example, whether gas production would continue at viable rates over lengthy time periods, or whether initial production would drop as the underground hydrate-bearing sands adjust to the production process, Boswell said.

However, although often referenced as “production tests,” the next phase of tests would best be characterized as a series of carefully controlled scientific experiments, determining how gas production responds to effects such as depressurization, Boswell said. By separately varying a series of parameters, such as the pressure and temperature, the researchers will be able to determine the production characteristics of the hydrate resource. Feeding these characteristics into a computer model of the methane hydrate “field” should then enable an assessment of how best to sustain and maximize production, and hence provide insights into the economic feasibility of hydrate development.

Finding a North Slope

On the central North Slope of Alaska the teams involving BP and ConocoPhillips are investigating suitable locations for the production tests, with both teams envisaging drilling and testing within the same approximate timeframe, Boswell said. Testing will require agreements with the appropriate oil and gas leaseholders, as well as viable plans for developing and supporting the necessary test infrastructure, he said.

“We’re optimistic that we’re going to be conducting a test in the Greater Prudhoe Bay area within the next year,” Boswell said.

The testing could take up to two years to complete but might possibly end sooner than that if the researchers meet with early success, as they experiment with different production techniques.

“We might find (for example) that all you have to do is depressurize these (deposits) and it works,” Boswell said. 

Japanese test in 2012

Meantime, the Japanese are talking about conducting their first offshore production test in 2012. That test, the first in a marine environment, will be exceptionally expensive although also very exciting and important, Boswell said.

However, it’s still too early to say when or if methane hydrate production will become a commercial reality – Boswell characterized the current DOE-funded research as using sound science to glean information about a potential new energy source, providing knowledge for a future evaluation of methane hydrate development. 

What about global warming?

And Boswell also commented on concerns that some people have expressed, that the development of methane hydrate deposits might increase global warming risks: Methane is a greenhouse gas several time more potent than carbon dioxide, the gas that many scientists believe is causing the climate to warm.

Scientists are concerned that the natural breakdown of methane hydrate deposits as global temperatures rise is releasing methane into the air and thus accelerating the rate of climate change. And there is a tendency for people to confuse this issue with the issue of developing methane hydrate as an energy source, Boswell said.

In fact, methane hydrate deposits exist in a wide diversity of situations, in a variety of sediments, at depths ranging from near surface to perhaps 3,000 feet, and at temperatures ranging from well below freezing to around 20 C.

And situations, perhaps near the surface where methane hydrate will tend to dissociate naturally, are very unlikely to be suitable for methane hydrate development as an energy source: People will prefer to develop deposits in geologic settings where the resource is well sealed from natural escape and can be directed into a gas production well.

“In fact, the two pieces of the resource are probably mutually exclusive … The methane hydrate that people will target as a resource … should also be the methane hydrate that’s least likely to be impacted by climate change,” Boswell said. “The main reason is that most people are looking at methane hydrate to produce that’s fairly deeply buried.”

Contact Alan Bailey at publisher@greeningofoil.com