Could burying the greenhouse gas help solve one of our most pressing environmental problems?

Can we store our CO2 under this? A slope of basalt rocks in Rhoen National Park, Germany.

After two centuries of extracting carbon from the Earth, researchers are trying to figure out how to reverse that process.

Scientists have devised numerous schemes for reducing carbon dioxide emissions, which have reached 24 billion tons of CO2 per year—a quarter of it originating in the U.S. These schemes run the gamut, from trapping the greenhouse gas in the ocean to capturing it with windmill-like structures and then turning it into limestone mountains.

These days, the idea of burying CO2 thousands of feet beneath the ground⎯a practice known as sequestration⎯is gaining momentum, as well as tens of millions of dollars in federal funding. Since 2005, the Department of Energy has earmarked $145 million to go toward seven regional partnerships that are testing the feasibility of sequestration.

Long-term underground storage requires capturing CO2 by separating it during natural gas production or removing it before or after combustion at power plants. The gas would then be compressed into liquid form, transported by pipeline or ship to the storage site and injected it into deep, porous rock formations beneath an impermeable cap such as shale, which is a sedimentary rock derived from clays.

The process isn’t novel. For decades oil drillers have injected CO2 into the ground to drive more oil out of it. Statoil, a Norwegian oil company, has buried millions of tons of carbon in a saline aquifer beneath the North Sea to avoid steep carbon taxes.

If active U.S. pilot projects succeed, billions of tons of carbon could be naturally converted into underground minerals. However, even if the technology proves environmentally viable in the U.S., it must be cost effective.

Experts say that won’t happen until the country puts some sort of price tag on CO2 emissions.

“If we really want to implement these technologies large-scale, we’ve got to look at the economic cost,” says Susan Capalbo, director of the Big Sky Carbon Sequestration Partnership, one of seven groups funded by the DOE.

Norway imposes a carbon tax on industrial companies of around $50 per ton of CO2 emitted into the air, a potential cost to Statoil of $50 million for the 1 million tons of CO2 it produces each year. However, instead of paying out of pocket, the energy company invested in carbon capture and storage technology, so they could bury the gas instead. The price tag was $80 million more than a system that would release CO2.

“Even accounting for operating expenses,” said Statoil energy advisor Olav Kårstad, “this is obviously also a good economic case when operating under this tax regime.”

But, there is no such economic incentive to capture and sequester in the U.S.

First off, capturing emissions is expensive. According to the Electric Power Research Institute, retrofitting a coal plant for CO2 capture uses nearly a third of its power and more than doubles the cost of electricity for consumers. Two power plants planned for Washington will be designed to capture CO2 emissions. Sequestration will require 3.5 percent of the funds proposed for the $1 billion project.

Economists are working on the logistics and costs of capturing, transporting and injecting CO2, as well as monitoring and remediation expenses for large-scale projects. The calculations assume that someday a price will be placed on carbon, and entities interested in avoiding the tax will pay for sequestration services.

That time may not be too far off, says Big Sky Partnership economist Charles Mason, pointing to recent suggestions for cap-and-trade schemes in Wyoming, and U.S. companies voluntarily capping carbon emissions on the Chicago Climate Exchange. In addition, just weeks ago, California passed legislation that will require industry to lower CO2 emissions 25% by 2020.

“I think it’s odds on that we’ll have some sort of carbon tax or cap-and-trade scheme in place within 10 years,” says Mason.

The first step, however, is making sure the technology works.

Researchers in Texas are testing the process. Last year, they pumped 1,600 tons of CO2 1,500 meters into a sedimentary saline aquifer in the Frio Formation, just out side of Houston.

When CO2 is injected into geologic formations, the majority dissolves in water there, like bubbles in seltzer. After thousands of years, the CO2 mineralizes—converted into a solid like calcium carbonate, the chief constituent of limestone.

There were some surprises in the Texas study, said Yousif Kharaka, a geochemist leading the Energy Department-funded project.

When the CO2 dissolved, the pH of the water trapped in the rock dropped from 6.4 to 3.0—from the acidity of milk to that of vinegar. In that environment, “the water starts attacking minerals,” said Kharaka, whose research appeared in the journal Geology in June. Some minerals such as calcite or iron oxyhydroxides seal pores and fractures, forming an impermeable barrier at the highest level of the rock formation. If the high acidity water dissolves those minerals, there’s no barrier, and a path could open for the CO2 to escape and for water loaded with iron, manganese, and other “nasty metals” to contaminate aquifers that supply water for drinking and irrigation.

“If we were to put in everything we’re adding to the atmosphere now, we’re talking about 25 billion tons of CO2 worldwide,” Kharaka said. “We have to be careful where we do it.”

The CO2 in the Frio Formation likely won’t mineralize for thousands of years, but researchers say the conversion could happen in a fraction of the time in basalt.

There are 85,000 square miles of volcanic rock in the Northwest U.S., which accumulated millions of years ago in layers as lava flows spread and cooled, forming stacks like pancakes, each sheet tens to hundreds of feet thick. The fast-cooled tops are full of cracks and gas bubbles. The slow-cooled, dense centers form impermeable barriers. Researchers estimate more than 100 billion tons of CO2—as much as all coal-burning U.S. power plants produce in two decades—could be stored in porous sections, trapped deep beneath the impermeable layers.
Next year, scientists will inject 3,000 tons of CO2 1,000 meters into a basalt formation in Washington state, and they expect the gas to mineralize within a year and a half—a significantly shorter timescale than the thousands of years the process takes in sedimentary formations.

“It is much, much faster than we thought it would occur when we started the work, and that’s been a really extraordinary finding,” says project leader Peter McGrail, a laboratory fellow at Battelle Pacific Northwest Division.

There is enormous potential for storage in basalts in China and India, home to the largest terrestrial basalt flow, said McGrail, but basalts may play only a small role in U.S. carbon storage because burying carbon in existing oil and gas wells might be cheaper. 

Sequestration foes, such as environmental groups Greenpeace and Friends of the Earth, argue that funds for burying CO2 should instead go to renewable energies, like wind and solar power. But other groups, including the National Resources Defense Council, see sequestration research as a necessity. Capture and sequestration from coal-fired power-plants—which produce more than half our power and emit a third of the country’s CO2—are a key additional strategy for climate protection, says Antonia Herzog, a scientist at the council’s Climate Center.

All these efforts, investigations, and considerations continue to take place even as the economics remain nebulous. But that’s ultimately what all these projects are preparing for, said Big Sky Partnership’s Capalbo.
“We have to be ready for when carbon controls are put in place.”

Originally published September 25, 2006


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