[Editors] MIT: Storing CO2 below ground may prevent polluting above

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT: Storing CO2 below ground may prevent polluting above
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For Immediate Release
WEDNESDAY, FEB. 7, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

GRAPHIC, PHOTO AVAILABLE

CAMBRIDGE, Mass.--A new analysis led by an MIT scientist describes a 
mechanism for capturing carbon dioxide emissions from a power plant 
and injecting the gas into the ground, where it would be trapped 
naturally as tiny bubbles and safely stored in briny porous rock.

This means that it may be possible for a power plant to be built in 
an appropriate location and have all its carbon dioxide emissions 
captured and injected underground throughout the life of the power 
plant, and then safely stored over centuries and even millennia. The 
carbon dioxide eventually will dissolve in the brine and a fraction 
will adhere to the rock in the form of minerals such as iron and 
magnesium carbonates.

Carbon dioxide is one of the primary greenhouse gases contributing to 
global warming. Studies have shown that reducing carbon dioxide 
emissions or capturing and storing the emissions underground in a 
process called sequestration is vital to the health of our planet. 
But one of the biggest risks of any sequestration project is the 
potential leak of the injected gas back into the atmosphere through 
abandoned wells or underground cracks.

In a paper published in a recent issue of Water Resources Research, 
MIT Professor Ruben Juanes and co-authors assert that injected carbon 
dioxide will likely not flow back up to the surface and into the 
atmosphere, as many researchers fear.

"We have shown that this is a much safer way of disposing of CO2 than 
previously believed, because a large portion-maybe all-of the CO2 
will be trapped in small blobs in the briny aquifer," said Juanes, a 
professor of civil and environmental engineering. "Based on 
experiments and on the physics of flow and transport, we know that 
the flow of the CO2 is subject to a safety mechanism that will 
prevent it from rising up to the top just beneath the geologic cap."

Researchers have considered the possibility of sequestering CO2 
beneath the Earth's surface in at least three types of geologic 
formations: depleted oil and gas fields, unminable coal seams and 
deep saline aquifers. Juanes' research dealt with the third 
category-porous rock formations bearing brackish water that are 
ubiquitous underground.

The study shows that carbon dioxide could be compressed as it leaves 
the power plant and injected through a well deep underground into a 
natural sublayer consisting of porous rock, such as sandstone or 
limestone, saturated with saltwater. Because of its buoyancy, the 
injected gas will form a plume and begin to rise through the 
permeable rock.

Once the injection stops, perhaps after the power plant has operated 
for decades, the plume will continue to rise, but now saltwater will 
close around the back of the gas plume. The saltwater and carbon 
dioxide will begin to juggle for position while flowing through the 
tiny pores in the rock and, because rock's surface attracts water, 
the water will cling to the inner surface of the pores.

These wet layers will swell, causing the pores to narrow and 
constrict the flow of carbon dioxide until the once-continuous plume 
of gas breaks into small bubbles or blobs, which will remain trapped 
in the pore space.

"As it rises, the CO2 plume leaves a trail of immobile, disconnected 
blobs, which will remain trapped in the pore space of the rock, until 
they slowly dissolve and, on an even larger timescale, react with 
rock minerals," said Juanes. "It is a good example of how a process 
that occurs at the microscopic scale affects the overall pattern of 
the flow at the geologic scale."

"We also found that by injecting water along with the CO2, we can 
optimize sequestration," said Elizabeth Spiteri of Chevron Energy 
Technology Co., who worked on this research while a graduate student 
at Stanford University, where Juanes taught before joining the MIT 
faculty. "I had always wanted to dig deeper into the physics that 
dictate the distribution of gases and liquids in the Earth's 
subsurface. This turns out to be essential for CO2 sequestration, as 
well as predicting groundwater contamination and enhancing recovery 
from mature oil fields."

The other co-authors are Martin Blunt of Imperial College London and 
Franklin Orr Jr. of Stanford University. The work was funded by 
industrial affiliates of the Petroleum Research Institute at Stanford 
University.

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Written by Denise Brehm, MIT Department of Civil and Environmental Engineering