by Christopher Swope,
Governing.com
On a ranch outside Cranfield, Mississippi, workers for the state's
largest oil and gas operator are shooting a dense liquid 10,300 feet
into the earth. The liquid is a supercritical form of carbon dioxide
that serves a valuable purpose for Denbury Resources Inc. Oozing
through porous rock, the CO2 mixes with oil and pries it out from
underground nooks that otherwise would be hard to reach. Denbury pumps
the slimy blend back out of the ground, sells the oil and sends the
carbon dioxide back down, repeating the cycle until a well runs dry.
What geologists want to know is what happens to the CO2 that's left
behind.
For each barrel of oil produced using this method of "enhanced
oil recovery," Denbury says that perhaps 2,500 times as much carbon
dioxide remains in the ground. If that proves true, variations of this
long-used technique for producing more fossil fuel also holds promise
for reducing greenhouse gas emissions.
Minimizing the risks of climate change is not really the goal for
Texas-based Denbury. The focus at its Mississippi operations is oil,
not global warming. But 500 miles away, geologist Susan Hovorka is
paying close attention to the oil company's work and its environmental
implications. Hovorka is one of the foremost experts on the emerging
science of carbon sequestration, and Denbury has allowed her and her
team of researchers from the Texas Bureau of Economic Geology to rig
the company's wells with subterraneous monitors that beam data back to
their computers in Austin.
Every 10 minutes, Hovorka can see how the
injections build pressure in underground formations, how the carbon
dioxide is moving and behaving, and whether it poses a threat to
drinking water near the well sites two states away. "If we can
understand what's happening in this rock," Hovorka says, "then we can
scale up with confidence."
Hovorka's work is one of more than two dozen research projects around
the country focused on carbon sequestration. About half of them
piggyback on oil projects, while others are more purely experimental.
What all of them are testing is the ability of different geological
formations, called "sinks," to absorb carbon dioxide and hold it --
hopefully forever.
Geologists in Illinois and New Mexico recently injected small amounts
of carbon dioxide into coal seams that are so deep in the earth they
can't be mined. In Michigan, the target was a saline formation 3,500
feet below the surface. Researchers also are testing the ability of
forests, farm soil and wetlands to hold carbon, a process known as
"terrestrial sequestration."
Most of the "geologic sequestration" tests so far have been tiny in
scale. A large-scale sequestration project tied to the U.S. Energy
Department's "FutureGen" plant was scrapped in January because of cost
overruns. But the department believes its other research experiments,
including the one in Mississippi, are ambitious enough to determine
whether long-term sequestration is viable.
The potential is certainly there. According to an Energy Department
survey, underground pockets in the United States and Canada might be
able to store between 1.2 trillion and 3.6 trillion metric tons of
carbon dioxide. That's more than 200 times the 5.9 billion metric tons
of CO2 emissions the United States currently produces every year. But
not every state is a candidate to store carbon dioxide. Minnesota, New
Hampshire and Vermont, among others, simply don't have the right
underground geology.
Burial Grounds map
In states with a lot of potential sinks, there's a growing interest in
where sequestration science is headed. Some are funding research
through state agencies, universities and geological surveys. A few
legislatures have begun writing laws to handle the legal and
environmental aspects of pumping large quantities of carbon dioxide
into the ground. State utility regulators also have been looking at
carbon storage for several years, ever since electric utilities began
proposing to build dozens of coal-fired power plants around the
country. That sequestration is still an unproven technology is one
reason many states have been denying permits for new coal plants --
mostly in favor of natural gas plants, which emit less greenhouse gas
but costs more.
Most proposals for dealing with global warming focus on using less
fossil fuel. That's not what sequestration is about. The premise behind
storing carbon underground is that it would allow consumers and
industry to continue using cheap-and-dirty fuels such as coal for years
to come, without guilt. "This is a critical technology to help us solve
the problem of using an important energy source and using it in a more
environmentally benign manner," says Howard Herzog, a chemical engineer
who heads a carbon sequestration initiative at the Massachusetts
Institute of Technology. "I'm not saying it's a 100 percent slam dunk
that it will work. But the chance of success is high and we should be
investing in making it happen."
Critics say sequestration research is a distraction from the pursuit of
clean-energy alternatives, such as wind and solar power. The goal of
sequestration, after all, is to enable our addiction to fossil fuels,
rather than break it. In any case, carbon storage for the purpose of
reducing emissions is probably a decade or more away. The big hang-up
is in developing efficient and affordable methods for capturing carbon
dioxide as it comes out of power plants. For now, most of the CO2 used
in both enhanced oil recovery and the sequestration pilot tests comes
from naturally occurring sources rather than smokestacks.
Safety is another concern. When it comes to storing vast amounts of
carbon dioxide in the ground, scientists and policy makers alike want
more certainty -- about whether the CO2 might harm drinking water
supplies, whether so much pressurized gas in the ground might cause
small earthquakes, and whether they can confidently say that carbon
dioxide, once sent underground, will stay there forever. In working to
solve the environmental disaster of climate change, the last thing
anyone wants to do is create another environmental disaster.
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