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Feature Story
How to Clean Coal
Page 3

Burial Chambers

Weyburn, a town of 10,000 in southeastern Saskatchewan, was the next stop on my journey as I followed the trail from carbon capture to carbon sequestration. North Dakota, much of which is impressively flat, looks like Tibet compared with this part of Canada's prairie provinces. The horizon was a ruler-straight line where the ocher grain fields met the big topaz sky. "It's so flat here that if your dog runs away, you can see him for three days," one oil roustabout told me, repeating a favorite local one-liner. I didn't spot any running dogs, but I did see lots of oil wells, each one marked by a pump jack that bobbed its iron head like a thirsty horse. "This oil field, the Weyburn Unit, measures 10 miles by 7 miles," said Dave Craigen, an EnCana community relations representative. "Over that 70 square miles, there are about 700 producing oil wells."

Craigen and I, both clad in protective EnCana coveralls, safety glasses, and hard hats, stood outside a tall, barbed-wire-topped fence enclosing the white CO2 pipeline where it emerges from the wind-whipped prairie. It wasn't much to see, really -- just a bit of industrial plumbing. I had to remind myself that this was no ordinary bit of gas pipe. This was ground zero in the first large-scale test in North America of geologic sequestration of CO2 from gasified coal. "Over the life of our CO2 injection project on this oil field," Craigen told me, "20 million tons of CO2 will be sequestered. That's 20 million tons of CO2 that would otherwise be going up the flue stack at the gasification plant."

Photo of a plastic igloo on a Saskatchewan oil fieldWe got into Craigen's black pickup truck and drove a mile or so down an asphalt road, then turned into a gravel driveway that led to a brown igloo-shaped structure. "This is one of our CO2 injection wells," my tour guide said as he opened a gate in the fence, then unlocked a door in the plastic igloo. "We have 88 of these distributed around the Weyburn unit." He stepped inside the dark dome. It housed a stack of bolted-together pipeline fittings as tall as he was -- an iron Christmas tree bristling with star-shaped manual shut-off valves. "We inject 110 million cubic feet of CO2 per day," he said. At that rate, EnCana is burying more CO2 in a year than 100,000 cars release in their operating lifetimes.

"A 50-year-old producing oil field is practically unheard-of," Craigen explained. "But with the CO2 flooding, we expect to recover an additional 120 million barrels over the next 20 years or so."

I realized I was witnessing a burial of sorts. Fossil carbon, which I had seen extracted from the ground as coal at the Freedom Mine and wrung of its energy value at the gasification plant, was here being recommitted to the earth. Ashes to ashes, dust to dust, carbon cradle to carbon grave. If coal is to have a future as a major fuel in the twenty-first century and beyond, this is what it might look like: smokestacks effectively turned upside down, shooting CO2 into subterranean rock formations rather than up into the sky.

But if the CO2 in question is used to produce oil, which in turn will lead to more greenhouse-gas emissions, is there a net benefit to the planet? Sasha Mackler, the analyst for the National Commission on Energy Policy, believes there is. "If the sequestered CO2 were just promoting more oil consumption," he says, "then you'd have to question how much good it's doing. But by enhancing oil recovery, you're not necessarily increasing the demand for oil. You are basically offsetting oil production that would happen elsewhere, perhaps in the Middle East. You also have to consider that enhanced oil recovery using CO2 is happening now, and will continue to happen in the future. If, instead of using naturally occurring CO2 from a well, you can use CO2 from things like the combustion of coal, then you are very substantially decreasing what would otherwise be emissions to the atmosphere. From a climate standpoint, that's clear progress."

That assumes, of course, that the sequestered carbon is staying put. I asked Craigen if the CO2 would remain in its mile-deep burial vault. "Since we started the CO2 flood in 2000," he replied, "we've been cooperating with a consortium of scientific organizations led by the International Energy Agency to study that question." In June 2004, researchers presented a report from a four-year study. In a nutshell, they said that sequestration is working. "In this particular oil-field geology," Craigen summarized, "the CO2 is staying down there."

Although results from Weyburn are encouraging, it's too soon to conclude that geologic sequestration can play a major role in solving the world's climate-change problem. For one thing, relatively few of the country's largest population centers, and the power plants that serve them, happen to be located near oil fields. But researchers are considering other types of geologic formations as candidates for CO2 sequestration. The most plentiful and widely distributed of these are called saline aquifers, or brine formations. "Brine formations are found where there's the same kind of highly porous rock where you'd find oil and gas reservoirs," says Sally Benson, head of the carbon sequestration program at Lawrence Berkeley National Laboratory in California. "But there was no source of hydrocarbons in these sponge-like reservoirs, so they ended up being filled with water instead of oil or gas. The water can be up to five times saltier than seawater, because of salts that have dissolved out of the surrounding rocks. The high level of salinity suggests that these formations are isolated from sources of circulating fresh water," and thus pose little risk of contaminating aquifers.

The evidence collected so far in about a dozen small-scale monitoring projects around the world, Benson says, supports the viability of geologic CO2 sequestration in deep brine aquifers. "If you have a good, isolated formation with an impermeable cap rock as a lid to keep the CO2 from escaping upward, then the gas should stay down there indefinitely. The bigger question now is, how much CO2 could you put in these brine formations? Some rough calculations done in the 1990s came up with some very large capacities -- as much as 50,000 billion tons of CO2." That would be enough to entomb every last ounce of projected CO2 emissions for centuries.

Europe is ahead of the United States in testing large-scale CO2 sequestration. That's because there are already mandatory restrictions on greenhouse-gas emissions in most of Europe. (The European Union and several additional countries in Eastern and Western Europe ratified the Kyoto Protocol limits on greenhouse-gas emissions in 2002, and the terms of the agreement went into effect early this year.) Even before Kyoto, Norway's state-owned oil company had begun capturing about a million tons of CO2 per year from offshore petroleum platforms and injecting it into a geologic formation deep below the bed of the North Sea.

So far, though, nobody is capturing and sequestering CO2 from an electrical power plant. In June 2005, British Petroleum and three partnering companies announced an ambitious project to change that. The partnership plans to add equipment to an existing natural-gas-fueled power plant near Peterhead, Scotland, that will convert natural gas to CO2 and hydrogen. The CO2 will be piped to a nearly depleted North Sea oil reservoir, where it will be injected 2.5 miles beneath the ocean floor for enhanced oil recovery. The hydrogen will be used as a "decarbonized" fuel to generate electricity. When the project fires up (current plans call for a 2009 start), it's expected to capture and store around 1.4 million tons of CO2 each year and provide carbon-free electricity to the equivalent of 250,000 homes.

Generating carbon-free electricity from coal is somewhat more complicated and expensive than the natural-gas-based process to be used in the Scottish project. But it can be done, using a combination of technologies known as integrated gasification combined cycle (IGCC). Four IGCC power plants are up and running today -- two in Europe and two in the United States. One of the U.S. plants is located on the Wabash River in Indiana; the other, a newer, state-of-the-art facility, sits on land reclaimed from an abandoned phosphate mine near Tampa, Florida. After saying good-bye to Dave Craigen at the Weyburn oil field one chilly May afternoon, I headed down to Tampa to warm up and to see how IGCC might fit into coal's future.

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Photo: Mark Duffy
Map: Small World Maps

Illustration: Jim Kopp

OnEarth. Fall 2005
Copyright 2005 by the Natural Resources Defense Council