Editor's Note: This is the third in a series of five features on carbon capture and storage, running daily from April 6 to April 10, 2009.

For more than a decade, Norwegian oil company Statoil Hydro has been stripping climate change–causing carbon dioxide (CO₂) from natural gas in its Sleipner West field and burying it beneath the seabed rather than venting it into the atmosphere.

The company estimates that since 1996 it has stored more than 10 million-plus metric tons of CO₂ some 3,300 feet (1,000 meters) down in the sandstone formation from which it came—and all of it has stayed put, which means storage may be the simplest part of the carbon capture and storage (CCS) challenge.

The basics of carbon dioxide storage are simple: the same Utsira sandstone formation that has stored the natural gas for millions of years can serve to trap the CO₂, explains Olav Kaarstad, CCS adviser at Statoil. An 800-foot (250-meter) thick band of sandstone—porous, crumbly rock that traps the gas in the minute spaces between its particles—is covered by relatively impermeable 650-foot (200-meter) thick layer of shale and mudstone (think: hardened clay). "We aren't really much worried about the integrity of the seal and whether the CO₂ will stay down there over many hundreds of years," Kaarstad says.

The company monitors its storage through periodic seismic testing, a process that is not unlike a sonogram through the earth, says hydrologist Sally Benson, director of the global climate and energy project at Stanford University. That monitoring indicates that between 1996 and this past March, the liquid CO₂ has spread to occupy some three square kilometers, just 0.0001 percent of the area available for such storage.

"We're not going into a salt cavern, we're not going into an underground river. We're going into microscopic holes," explains geologist Susan Hovorka of the University of Texas at Austin, who has worked on pilot projects in the U.S. "Add it up and it's a large volume" of storage space.

How large? The U.S. Department of Energy (DoE) estimates that the U.S. alone has storage available for 3,911 billion metric tons of CO₂ in the form of geologic reservoirs of permeable sandstones or deep saline aquifers, according to a 2008 DoE atlas. These reservoirs are more than enough for the 3.2 billion metric tons of CO₂ emitted every year by the roughly 1,700 large industrial sources in the country. Most of that storage is near where the majority of coal in the U.S. is burned: the Midwest, Southeast and West. "There are at least 100 years of CO₂ sequestration capacity and probably significantly more," Benson says.

The storage seems to be long-term as well; the sequestered CO₂ doesn't just sit in the rock waiting for a chance to escape. Over decades it forms carbonate minerals with the surrounding rock, or it dissolves into the brine that shares the pore space, Hovorka notes. In fact, when she tried to pump CO₂ out of her test site south of Dayton, Tex. using natural gas extraction techniques, the attempts failed completely.

5 Comments

1. 1. 2008RealityCheck 03:23 PM 4/8/09

   What is the ultimate CO2 ppm goal for the atmosphere and why doesn't the author ask? What are we trying to accomplish? Is it to hold it at 385ppm, reduce it to 250ppm, lower it further? What if the rest of the world find out that CO2 has no relevance to climate change (as certainly seems to be the case if you look at the 540 million year record)? Will we abandon CO2 sequestration or continue because that's where we get tax revenue from? What if we find that agricultural production decreases because we are reducing the available and absolutely critical CO2? Who is advocating for Earth's flora? Who is advocating for the third world population which undoubtedly would starve if we lost the 30% agricultural gains because of the CO2 gain over the past 250 years? Do you even care?

   Reply | Report Abuse | Link to this

2. 2. Ricardo in PR 09:53 PM 4/8/09

   These efforts are quite exciting as they show that there are simpler alternatives to control the CO2 concentration of the atmosphere than those that involve large scale efforts at controling the amount of solar radiation hitting the earth or the absortion of CO2 by the oceans.

   Reply | Report Abuse | Link to this

3. 3. eoleen 04:26 PM 4/9/09

   "is covered by relatively impermeable 650-foot (200-meter) thick layer of shale and mudstone (think: hardened clay)." and "We aren't really much worried about the integrity of the seal and whether the CO2 will stay down there over many hundreds of years," Kaarstad says."
   
   You have GOT to be kidding... I strongly suggest that you look at the phase diagram for CO2: it will tell you that under the conditions specified it is a liquid - barely: let the pressure be released - such as an earthquake, or by some idiot drilling into it or something - and all of that CO2 will come boiling out into the atmosphere before you can say "carbon dioxide"...
   
   And to think that "many hundreds of years" is PERMANENT storage... What are our ever-so-great grandchildren supposed to do?
   
   Such suggestions are criminal.

   Reply | Report Abuse | Link to this

4. 4. Theodore 12:49 PM 6/13/09

   The best form of carbon sequestration involves the process of combining the carbon not with oxygen, but with hydrogen in long chain molecules. This has the advantage that it is a solid at room temperature. It can be stored underground safely for millions of years. Perhaps old coal mines would be a suitable place to put these solid chunks.

   Reply | Report Abuse | Link to this

5. 5. eoleen in reply to Theodore 01:48 AM 6/15/09

   Theodore... I can't figure out if you are pulling my leg or not... but just in case you aren't, then carbon combined with hydrogen "in long chain molecules" is really heavy crude oil, or tar, as in "tar sands", and it would take more energy to create this stuff than you get by burning the carbon to begin with. THIS IS NOT A SOURCE OF ENERGY!!!!! This is, rather, a waste of bandwith...

   Reply | Report Abuse | Link to this