Research takes aim at carbon
10-year, $20-million program tackles ‘one of hardest problems that this world has ever encountered’

We 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 problem.

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 support.

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 goal.

Capture group

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,

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.

Storage group

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 geological sequestration.

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 more closely.

“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.

Science group

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.

Policy 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.

Integrative 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.

Stabilization wedge

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 wedge.

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 start.”

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

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 leaks?

While 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 carbon dioxide.

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 meet.

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 severe conditions.

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

If, of course, the sludge were actually less permeable than the cement, this would not be a problem.

“The mush is really important,” Dr. Bruant said.

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.

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