A war of words broke out last week over a report suggesting that carbon capture and sequestration (CCS) could be a costly fiasco.
Groups ranging from the American Petroleum Institute to the Pacific Northwest National Laboratory released lengthy rebuttals of a study published this year in the Journal of Petroleum Science and Engineering. It was described last week in the United Kingdom-based Guardian. The study's authors, on the other hand, stand by their conclusions.
"I know we are right," said study co-author and avowed climate skeptic Michael Economides of the University of Houston. He wrote the paper with his wife, Christine Ehlig-Economides of the Department of Petroleum Engineering at Texas A&M University.
Their research argued that previous modeling of storing carbon dioxide underneath the ground underestimated by "5 to 20 times" the amount of space needed for sequestration of the gas. According to the authors, one commercial power plant would produce emissions requiring a permanent storage spot the size of a "small U.S. state."
"The findings of this work clearly suggest that [geological sequestration] is not a practical means to provide any substantive reduction in CO2 emissions, although it has been repeatedly presented as such by others," the study says.
The duo's conclusions created a stir on the Internet, where environmentalist Joe Romm of the Center for American Progress wrote: "Realistically, it has always been hard to see how CCS could be more than a small part of the solution to averting catastrophic climate change." Similar postings popped up on sites such as The Huffington Post.
CCS, which is considered critical for the survival of coal in a carbon-constrained world, has never been proved at commercial scale, and many analysts believe it could be a decade or more before it becomes a reality. Coal fires about 45 percent of U.S. electricity.
A heavyweight counterattack
But a slew of engineers, geologists, business leaders and green groups slammed the study as riddled with shoddy assumptions and inaccurate conclusions.
"This is two people against the entire scientific community," said George Peridas of the Natural Resources Defense Council, who wrote an extensive critique of the study on the Internet.
The Pacific Northwest National Laboratory, API, Lawrence Berkeley National Laboratory and British geologists from Edinburgh University and Imperial College London also joined in on the attack. A paper from the Pacific Northwest National Laboratory, for example, said Economides and Ehlig-Economides' assertions "are flawed and stand in stark contrast to the enormous body of literature and field experience on CO2 injection."
For critics, a major flaw in the couple's analysis is that they focused on only a "closed" reservoir for carbon dioxide storage. That envisions gas stored in porous rock, where it is sealed off by rock or a natural barrier not just from above, but on all sides of the storage spot.
That runs counter to the likely scenario for many potential sequestration locations, said Sean McCoy, a senior engineer at Carnegie Mellon University.
A carbon-capture project operated by the Norwegian company Statoil in the North Sea, the Sleipner Project, captures CO2 from natural gas and stores it under the ocean, for example. It is not a "closed system," but one where the gas can move laterally.
Plenty of room, says DOE
Many likely storage spots for carbon dioxide are like rocky "sponges" that only need a thick layer of impermeable rock or clay in one place -- above them -- to prevent leakage of the gas, said McCoy.
"I am of the opinion that this paper should never have made it though peer review in the published form," he said.
Other detractors said Economides and Ehlig-Economides were wrong to assume that an underground storage area for CO2 would be only 200 feet thick, or that a small portion of a pore space within rock would be available for long-term sequestration. All are faulty assumptions that would drastically change the ultimate conclusion of the paper, they said.
The Department of Energy estimates that there is enough capacity to store up to 12,900 billion metric tons of CO2, one analyst said. In comparison, the United States spews a fraction of that every year -- about 5.8 billion metric tons.
In an e-mail, Ehlig-Economides, who Peridas called a "respected petroleum engineer and professor," said the Sleipner project in the North Sea is not a good measure of comparison because the volume of carbon dioxide stored there is "much less than what a single 500 megawatt power plant produces, let along several." She said she was writing lengthy responses for later release to address all technical points raised by others.
And her husband claimed that rebuttals were coming from people with a "vested interest" in so-called clean-coal technology. He said he was enjoying the attention, because they had "clearly struck a nerve."
To his critics, he offered a word of advice: "Go back and take a fresh look at what we said. Take a geoengineering class."
Correction: The amount of CO2 the United States emits annually is about 5.8 billion metric tons; an earlier version incorrectly stated the amount in millions rather than billions.
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