Research takes aim at carbon
program tackles ‘one of hardest problems that this
world has ever encountered’
could all ride bikes to work. That’s one idea, and
not a bad one, at that. Yet while the world is coming around
to the idea that global warming is a serious problem and
one that only human action can assuage, people are not prepared
to make drastic changes in lifestyle in order to solve the
The greater scientific community agrees
that human activity is generating too much greenhouse gas
to be spewed into the atmosphere, thus causing our climate
to change. The greenhouse gas that deserves the brunt of
the blame is carbon dioxide.
The Carbon Mitigation Initiative (CMI)
at Princeton is working on this carbon dioxide problem with
all the vigor it merits. CMI is a 10-year, $20-million program
jointly funded by British Petroleum and the Ford Motor Co.
CMI’s mission is to find solutions
to the problem that are feasible from scientific, economic,
social, and technological perspectives. Now in its fourth
year, CMI has 60 researchers on its roster.
“This is one of the hardest problems
that this world has ever encountered,” said Robert
Socolow, professor of mechanical and aerospace engineering
(MAE) and CMI codirector. The other codirector, Steve Pacala,
is professor of ecology and evolutionary biology. “It’s
wonderful to be working on this problem from complementary
perspectives—the three-legged stool of science, policy,
and technology,” Professor Socolow said.
The greater purpose is to seek out and
find solutions. To do so, they are researching first, how
much the world really needs to reduce emissions to stabilize
atmospheric carbon dioxide at a safe level. Yet the bulk
of research aims to determine the feasibility of emission-reduction
strategies, including their effectiveness, cost, and public
With this list of issues, it would be
easy for a project to lose its sense of direction, but CMI
is managing to stay focused. The initiative is divided into
four subgroups, each with a general research duty. A fifth
subgroup serves an integrative capacity, pulling the four
together and guiding the entire initiative toward a common
by Frank Wojciechowski
Robert Socolow is a professor
of mechanical and aerospace engineering and codirector
The first group is the capture group,
led by Robert Williams, senior research scientist at
the Princeton Environmental Institute. The capture group’s
main task is to develop low-emissions power sources, with
a particular focus on hydrogen, but this group is also studying
synthetic fuels and biomass.
MAE professor C.K. Ed Law and assistant
professor Yiguang Ju are studying the combustion of
alternative fuels as part of the capture group. Professor
Law is studying one possible alternative—hydrogen fuel,
although hydrogen has had a stigma
attached to it since the Hindenberg.
One of hydrogen fuel’s problems
is that it is a highly flammable gas and could cause explosions.
Another problem is that in order for hydrogen to provide
enough power for most needs, it must be supercharged. Yet,
the supercharging process damages fuel efficiency.
Professor Law and his group are trying
to find solutions to hydrogen’s combustion and safety
problems. Research has thus far shown that mixing propane
with hydrogen can help satisfy both of these issues, although
more research is being done.
Professor Ju’s group is studying
a synthetic fuel called dimethyl ether. The group hopes to
create successful combustion models for numerical prediction
and extend the current research for industrial applications.
The second group is storage, headed by
Michael Celia, professor of civil and environmental
engineering (CEE). A leading plan for preventing more carbon
dioxide emissions is to collect excess carbon dioxide, inject
it deep underground, and trap it there—a process called
The storage group is studying the complications
of this process, specifically the potential for carbon dioxide
leakage out into the atmosphere and the effects of injected
carbon dioxide on the environment. This group is where most
of the CMI members from the School of Engineering and Applied
Science (SEAS) can be found.
The storage group is full of SEAS faculty
and staff trying to answer the question of whether geological
sequestration of carbon dioxide will work.
Possible routes that carbon dioxide could
use to escape from its rocky prison are through cracks and
fissures and through abandoned wells. A few years ago the
storage group identified that abandoned wells provide the
largest potential for leakage pathways.
“I was discussing this with my colleague,
Stefan Bachu from the Alberta Energy and Utilities Board,
and we started to look at the number of wells in places like
Alberta, with about 350,000 oil and gas wells, and Texas,
with more than a million oil and gas wells,” Professor
Celia said. With CEE graduate student Sarah Gasda, Professor
Celia and Dr. Bachu analyzed the wells in the Alberta Basin
“We now realize that in some likely
injection locations, the injected carbon dioxide plume will
contact several hundred existing wells. Because those wells
could provide direct connections between the deep subsurface
and the land surface, they are of obvious concern.”
Professor Celia and CEE Professor Jean
Hérve Prévost are each working on simulating
the behavior of injected carbon dioxide.
Professor Prévost is working on “Dynaflow,” a
very advanced numerical modeling system that includes more
sophisticated treatment of chemistry and mechanics than any
other of its kind.
On the other hand, Professor Celia is
developing analytical models that are less complex but faster
as a screening tool. The complexity of simultaneously modeling
all the wells contacted by the carbon dioxide plume is incredibly
time-consuming with a high-end precision model like Dynaflow.
Assuming that some carbon dioxide does
come into contact with wells, questions will need to be answered
about how the carbon dioxide will react with the cements
that surround well casings, and the permeability of these
cements under high carbon dioxide conditions.
Eventually this information must be incorporated
into the models. Cement deterioration is a phenomenon being
studied by CEE Professor George Scherer’s group (see
related story on previous page).
CEE Associate Professor Catherine Peters studies
the geochemistry of deep aquifers that would be injected
with the carbon dioxide.
CEE department chair, Professor Peter
Jaffé, studies the environmental risks of carbon
dioxide leaking out, finding so far that leaks would not
likely affect drinking water quality adversely.
The storage group’s focus
for the next few years will be on empirical research, particularly
seeking to illuminate the effects of high carbon dioxide
conditions on well cements.
The science group, led by Jorge Sarmiento, professor
of geosciences, tries to make sense of the history of atmo-spheric
carbon—why the levels change, the nature and variability
of carbon sources and sinks, and the feasibility and impacts
of large-scale carbon mitigation. Engineers are not playing
a central role in this group.
The policy group is led by David Bradford
and Michael Oppenheimer, professors at the Woodrow Wilson
School of Public and International Affairs. This group studies
the costs and benefits of carbon mitigation, searches for
feasible paths to a low-carbon economy, and analyzes policies
that will support such economies. Engineers are not playing
a central role in this group.
Finally, the integrative group led by
Professors Pacala and Socolow brings the work of the four
groups together, using the findings of one group to guide
the research in another and steering the entire initiative
toward a common goal.
by Frank Wojciechowski
Graduate student Sarah Gasda is
working with CEE Professor Michael Celia and Stefan
Bachu from the Alberta Energy and Utilities Board
to analyze oil and gas wells in the Alberta Basin.
The integrative group has developed a
new concept to help people visualize the problem and guide
CMI’s greater research motive. The integrative group
has dubbed this visualization the stabilization wedge (see
graph on next page).
The stabilization wedge represents the
emissions CMI identifies as preventable over the next 50
years through mitigation. Several mitigation strategies would
each be responsible for cutting a slice out of the stabilization
These slices fall into categories such
as fossil fuel decarbonization, fuel efficiency, alternative
energies, and carbon capture and storage via geological sequestration.
“The point is there is a grab bag
of strategies to choose from,” Professor Socolow said. “We
don’t have to use them all, but we can use a combination
of several of them. Maybe it won’t be enough to solve
the problem, but it’s enough to make a very substantial
There is an opposing viewpoint held by
others in science and policy, that it would be better to
use the next 50 years solely for research, and wait to implement
mitigation strategies until the latter half of the century.
The assumption is that by the end of the 50-year period more
would be known about the problem, and thus more efficient
strategies would be available and understood to better treat
the problem, if in fact any action was necessary at all.
A carbon diet
Professor Socolow compares this situation
to weight loss. Assume one has been steadily gaining weight
and that one wants to lose a few pounds and stabilize at a
certain weight one year from now. He said the CMI stabilization
strategy is comparable to immediately starting a diet and exercise
regime, and losing a pound or two each month over the course
of the year.
He compares the opposing viewpoint to
a plan of gaining weight over the first six months, and then
trying to lose it all in the last six months. If in six months
a new miracle diet pill is on the market, one is in luck.
If not, however, one has an even worse situation to solve.
Professor Socolow said that many people
are latching onto the stabilization-wedge concept and its
action-oriented approach to the near future.
“Looking out 100 years is too far
to really know what the world will be like then, but looking
at the next 10 years is too short-term to inspire thought
about new technologies and investments,” he said. “People
can think about investing in a 50-year plan. People really
enjoy this concept because it gives them something to grasp
onto. I think it shows that this is a huge job, yes, but
it’s one we can imagine doing.”
Will well cements prevent carbon
Professors Celia and Prévost, Ms. Gasda, and others
try to determine whether wells that puncture a storage aquifer
will be sources of leaks. Professor Scherer and his group
study what could happen if the carbon dioxide (CO2) makes
contact with these wells. Will it deteriorate the cement,
and allow carbon dioxide to transport to the surface?
Early lab experiments whisper “yes...
but.” Yes, cements do deteriorate when bathed in CO2-rich
fluid, but the effectiveness of underground storage will
hinge on how much contact cements would actually have with
When a well is drilled, cement is poured
around the metal well casing. The cement holds the well’s
shape and fills in cracks in the surrounding rock that might
have been created during the drilling. If CO2 gets through
the rock, the cement will be the next defense against it.
When injected, CO2 carbonates an
aquifer, lowering the pH to about 3.
“It’s like Perrier®,” said
CEE research staff member Rob Bruant.
“Cements don’t like Perrier,” added
CEE graduate student Andrew Duguid.
Dr. Bruant and Mr. Duguid are working
with Professor Scherer in the cements lab. Mr. Duguid is
running experiments that reproduce the chemistry of the deep
underground where the “Perrier” and cement would
He creates three baths of acidic carbonated
water, one at room temperature, and two at higher temperatures
typical of deep underground environments. He adds samples
of various cements, as well as samples of cement poured into
cylinders of common porous rock such as limestone.
Mr. Duguid’s early experiments have
shown the cements are deteriorating very rapidly under these
After only nine days, the plain cement
sample began to deteriorate, creating a gooey, gray sludge.
Considering that scientists hope the CO2 will be contained
below ground for
hundreds of years, this data is especially
If, of course, the sludge were actually
less permeable than the cement, this would not be a problem.
“The mush is really important,” Dr.
Mr. Duguid plans to run tests on these
deteriorated cements to determine their permeability.
These experiments represent the worst
case scenario of carbon dioxide exposure to cement and it
is too soon to say whether this sort of damage could occur
in the field.
They are trying to discern just what the
chances are of CO2 coming into contact with the cements.
If gaps between the well walls and the cements developed
during drilling, they would provide a pathway for CO2 to
migrate upward and attack the cements along the way. How
common are gaps?
They also want to know how fast the “Perrier” will
be neutralized as it flows over cement.
Will it indeed present a problem for sequestration?
This project will provide the data to make a confident prediction.
previous story ] [
next story ]
of page ]