With their sights on stores of low-grade coal beneath the coasts of England, the ranches of Wyoming, and the fields of Inner Mongolia, entrepreneurs around the world are touting the promise of yet another "unconventional" approach to energy extraction.
The technique resembles the hydraulic fracturing technology that has produced an oil and gas boom across North America. (See related interactive, "Breaking Fuel From the Rock.")
The key element in this process, however, is not water. It's fire.
Underground Coal Gasification (UCG)—an old idea once embraced by Soviet leader Vladimir Lenin—is gaining new enthusiasts who say it can transform abundant but difficult-to-mine coal reserves into a cleaner fuel: synthetic natural gas. Instead of mining the coal, the companies propose to drill into the coal seam, ignite it, and capture the "syngas"—a combination of hydrogen, carbon dioxide, and methane—produced by the oxidation underground.
The syngas could be used just like natural gas to produce power, making it a potential solution for China, seeking an alternative to the coal-fired electricity that chokes its cities, and for Europe, eager to replace its own declining North Sea natural gas stores and reduce reliance on Russian imports. (See related, "Coal Burning Shortens Lives in China," and "No Freeze on Winter Energy Prices, Despite Natural Gas Boom.")
"We are potentially talking about a second North Sea here (in terms of gas production from coal)," said Algy Cluff, the wealthy, septuagenarian British businessman who helped pioneer the North Sea oil fields in the early 1970s. Cluff Natural Resources is leading an effort in the United Kingdom to apply UCG to the country's still-vast coal reserves. "It's far too big an opportunity for government and energy majors to ignore," he said.
Critics worry about the environmental consequences, including the potential for groundwater contamination, sinkholes and other types of subsidence, and underground fire. Also, greenhouse gas emissions would be significant unless steps were taken to integrate carbon capture and storage into UCG at the extraction site.
Advocates for the process insist that environmental concerns can be addressed. And systems for carbon capture and storage can be much more efficiently integrated into UCG site than into coal-fired power plants, they argue.
At the moment, though, none of the countries exploring UCG have policies in place that would force operators to take on the added expense of carbon capture. As with other types of unconventional energy development—oil sands, fracking, deepwater exploration—growing energy demand is propelling nations into the complexities and risks of new fossil fuel extraction techniques far more quickly than they are adopting policies to address the resulting carbon emissions. (See related "Quiz: What You Don't Know About Climate Change Science.")
A Mining Alternative
UCG first was proposed as early as 1868 in England by the engineering pioneer Sir William Siemens, who founded the company that became the multinational technology giant that bears his name. Siemens thought underground gasification could be a way to make use of waste coal left behind in mines.
And indeed, the idea today would be to apply UCG to the type of narrow coal seams that can't be mined conventionally. Oxidants, usually oxygen and steam, would be injected through a borehole under high pressure, causing the coal to combust. A second borehole would be used to pipe out the syngas.
Russian, American, Canadian, and British chemists all worked on fleshing out Siemens' idea. Britain planned to open an experimental plant in 1912, but that effort was thwarted by the start of World War I. Soviet dictator Lenin eventually embraced the technology, which he saw as a means to exploit Russia's great coal resources without having to send men down into dangerous, dirty mines.
The Soviets' UCG efforts continued, hit and miss, until the 1960s, when they were put aside by the discovery of huge natural gas reserves. One of the Soviet-era UCG sites, dating from 1961, is still in operation in Uzbekistan. In the West, there were a number of experimental efforts until the 1980s. But interest in UCG then waned—mainly because of the relative abundance of natural gas, and because American researchers learned the process could pollute nearby groundwater supplies.
But now, new technologies—first successfully used at a demonstration site in El Tremedal, Spain, from 1992 to 1998—have breathed new life into UCG. A key has been application of horizontal drilling techniques borrowed from the oil and gas industries, the same technology that's used in fracking.
Three nations with huge coal reserves, Australia, South Africa, and China, have led the way in testing updated UCG technology. The World Coal Association says that China, in fact, has 30 UCG projects in various phases of preparation. Carbon Energy, an Australian company, had planned to begin construction soon on a site in Inner Mongolia, using a process it had developed and tested in a demonstration project in Queensland. But delays in funding from its Chinese partner have slowed progress. Back in Queensland, the company is doing environmental testing at its demonstration site in an effort to prove to government regulators that UCG projects can be safely decommissioned, a step that will be necessary before Australia allows commercialization.
Perhaps the country where there's the greatest buzz about UCG is the United Kingdom, where Cluff and other proponents—including Britain's coalition government—believe it could make the nation less dependent on expensive natural gas imports. Britain's domestic North Sea production of natural gas peaked in 2000. Now, 47 percent of the gas consumed here comes from overseas, and that could rise to 75 percent by 2030.
Against this backdrop, UCG's potential seems irresistible for many. The Department of Trade and Industry estimates that the UK has 18.7 billion tons of deep seam coal reserves suitable for UCG, or about 300 years' supply. And that's not taking into account massive reserves under the North Sea.
So far, the UK Coal Authority has issued 24 conditional UCG permits to Cluff and several other companies, including Five-Quarter Energy and Riverside Energy. The permits allow companies to do only exploratory investigations, and approvals from many other national and local bodies would be needed before a UCG plant would be allowed to open; the process is so arduous that 13 of the conditional permits already have expired. Still, eight more applications are pending.
Cluff currently has five near-offshore permits for areas off Wales and Scotland. It also has a pending application for an inland site in Warwickshire. But UCG might have to overcome intense resistance from protesters. Frack Off, the lead protest group that has so far successfully slowed efforts to introduce hydraulic fracturing, or fracking, for shale-gas production in Britain, is already lining up against UCG, claiming it's as much of an environmental threat as fracking. Jon Gluyas, a geo-energy professor at Durham University, isn't convinced the public can be won over, either. "The thought of a fire burning below your feet doesn't even get to the starting line," he said.
Nevertheless, Tony Lodge, a spokesman for Cluff, is undaunted. He predicts Cluff could have a commercial operation up and running "by the end of this decade."
Meanwhile, in the heart of Wyoming's coal country, the Powder River Basin, Australian company Linc Energy has already received preliminary approval from state officials for a demonstration UCG project south of Gillette. But because of the risk of water pollution, Linc cannot proceed unless an 80-acre (32.3-hectare) segment of the Fort Union aquifer, now deemed suitable for livestock, is reclassified for industrial and commercial use. At a packed public hearing March 27, residents of the area voiced fears.
"If we do this and the bottom falls out of it, we're the ones that are going to pay for it—not the people who live in [the state capital of] Cheyenne, not the people who move on after they've done what they're going to do," said local resident Jim Thompson, according to a report in the Gillette News Record.
One of the worst episodes for UCG in fact occurred in Wyoming, not far from the site that Linc Energy is now eyeing for its new project. During the 1970s energy crisis, the U.S. Department of Energy's Lawrence Livermore National Laboratory spearheaded a test at Hoe Creek, Wyoming, south of Gillette. Pressure built in the cavity where the coal was burned to levels far higher than in the surrounding rock, pushing contaminants away from the cavity and polluting groundwater with benzene, a carcinogen. The cleanup effort took years and cost an estimated $10 million.
Researchers who have studied what went wrong at Hoe Creek believe that part of the problem was that the shallow coal strata was too close to potable aquifers. But the new horizontal drilling techniques allow engineers to reach and penetrate deep coal seams, at 550 meters (1,800 feet) or more. And that's lessened the risk of groundwater pollution, companies say.
"At that kind of depth, you're not close to any aquifers," said Michael Green, who runs the suburban London consulting firm UCG Engineering and is an adviser to Cluff.
David Camp, who leads Lawrence Livermore's UCG program today, says that having strong regulations in place and enforcing them will be key. "When UCG has been done poorly in the wrong location, there has been significant groundwater contamination," Camp said. "So you need to do things right."
Other environmental concerns: Sinkholes or ground subsidence can be a problem, just as is in traditional coal mining. Some also worry about the potential to start uncontrollable subterranean fires.
"There are a great number of ways in which coal fires can be ignited and burn underground," said Glenn Stracher, professor of geology and physics at East Georgia State College, who has written a book on the subject. (See related, "Pictures: Centralia Mine Fire, at 50, Still Burns With Meaning.") He noted in an email that even forest fires can ignite a coal seam—"as long as air can get to hot seams in the subsurface, via fractures, faults, etc., combustion may continue."
However, over the history of UCG, operators have had the opposite problem. Gluyas points out that the fires are so dependent upon pumped-in oxygen that, if the amount reaching the coal isn't sufficient, the flames quickly die out. "It's a delicate balance and can be excruciatingly difficult to get right," he said.
An important advance being applied at new UCG sites is a technology called controlled retractable injection point, or CRIP. A movable injection point can crawl along a borehole and allow operators to control the amount and pressure of oxidants released in a way that keeps the gasification process going.
Still, as Lawrence Livermore's Camp points out, so far, all the demonstration sites have been relatively small. Not one, with the exception of the site in Uzbekistan, is a large, commercial-size operation. "We are still on the learning curve," Camp said.
Underground Carbon Capture?
One of the most significant environmental problems is that syngas derived from UCG comes with a load of carbon dioxide, so its greenhouse gas emissions can be as great as those from coal. (See related story: "As U.S. Cleans Its Energy Mix, It Ships Coal Problems Abroad.")
Observers believe that UK regulators would be unlikely to give final approval to UCG without technologies to capture and bury its carbon dioxide emissions. The world's first commercial-scale power plants with carbon capture and storage technology are coming online this year, and they have been costly to build. (See related, "Clean Coal Test: Power Plants Prepare to Capture Carbon.")
However, it would be less expensive and more efficient to strip carbon dioxide from coal at a UCG site than at a power plant, proponents say. The volume of CO2 would be less than that coming out of a coal plant after combustion. "Gasification is carbon-capture ready," Camp said.
The captured carbon dioxide could be injected into the ground to aid in enhanced oil recovery, the commercial opportunity that Linc Energy is pursuing in Wyoming. CO2 injection also has possibilities in the North Sea, where it could extend the life of England's declining offshore oil wells. Early research indicates CO2 might also be safely shunted back into empty coal seams after they've been burned. (See related, "Germany Plans to Raze Towns for Brown Coal and Cheap Energy.")
Another byproduct of the syngas process that could be captured and put to use is hydrogen, which was viewed as a nuisance at early experimental UCG sites. Now, hydrogen is seen as having value in its own right as a clean alternative fuel. (See related story, "Fuel Cells Power Up: Three Surprising Places Where Hydrogen Energy Is Working.")
The opportunity both to produce hydrogen and to capture carbon makes UCG a potential "clean coal" technology, proponents say. But with no price on carbon in most countries, and only a very low price in Europe's fledgling carbon market, there's not much incentive for companies to add the extra expense of carbon sequestration to their UCG projects. "From a climate change point of view, that's trouble," said Camp. (See related, "Poland Hosts Climate Talks, While Boosting Coal Industry.")
Of course, the planet already is on track for trouble, given the current trajectory of greenhouse gas emissions. (See related, "New Climate Report Warns of Dire Consequences.")
If the world continues to rely on fossil fuel and its vast stores of coal to meet growing global energy demand, nations might indeed need to turn to dramatic solutions for sequestering carbon. (See related, "Can Coal Ever Be Clean?" and photo gallery, "The Visible Impacts.")
And those might include igniting coal when it's still underground.
(See related interactive map: "Four Ways to Look at Global Carbon Footprints.")
Marianne Lavelle contributed to this report.
This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.