DOUBLE TAKE: To Bury or Not to Bury CO2

Dec. 4, 2008 -- The scoop: Energy generation that is free of carbon dioxide (CO2) emissions, such as wind and solar, will not displace enough carbon-based fuels to prevent atmospheric concentration of greenhouse gases from reaching dangerous levels.

Two experts, Kurt Zenz House, cofounder of the Harvard Energy Journal Club, and Julie Shoemaker, a doctoral candidate at Harvard University, argue below that the best solution is to bury CO2 underground. A third, Peter Montague of Environmental Research Foundation, counters on page two with a completely different opinion.

Kurt Zenz House and Julie Shoemaker:

Carbon-based fuels are the basis of modern civilization. Oil accounts for about 90 percent of transportation and coal comprises about 50 percent of electricity production. But burning fossil fuels produces CO2, which is altering Earth's atmosphere and affecting the planet in dangerous ways. In order to minimize the risks, we need to decrease CO2 emissions dramatically over the coming decades.

Many people, including seasoned political leaders, investors, academics, journalists and entrepreneurs, argue that electricity generated by wind and solar power will soon displace fossil fuels and give birth to a renewable energy economy. We wish this were true. But there are several reasons why those solutions will not replace carbon-based fuels on their own in time to save the planet. In our opinion, the best way to reduce CO2 emissions is to bury it in deep geologic formations. It may sound fanciful, but it's actually easy to do. And in fact, the process is simply the oil and gas business in reverse.

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A few words on why renewable energy solutions alone will not do the job. Although they beat out carbon-based fuels when it come to environmental and security-related criteria, fossil fuels still out-perform renewable options on nearly all other measures. For example, fossil fuels beat renewable energy on cost and energy density. A modern coal-fired power plant, for example, will generate electricity for less than $50 per megawatt-hour. The same quantity of electric energy can be generated from wind and solar for about $120 and $250, respectively. And fossil fuels are much easier to store as gas or fluid than the electricity produced from renewable sources, which must be saved in batteries. For comparison, the best batteries store just 1 to 2 percent of the energy per unit mass as crude oil.

This doesn't mean that we should stop pursuing the use of renewable energy. It does mean that we need to be realistic about what can be done to reduce CO2 emissions now. We think the biggest potential lies with CO2 that is produced at power plants and certain chemical facilities. These large, stationary sources spew about 50 percent of all CO2 emissions into the atmosphere. If we could capture that gas at the source and bury it in porous rock deep underground, we could, in principle, reduce global CO2 emissions by about 50 percent without decreasing current use of fossil fuels.

Capturing and permanently storing CO2 in permeable rock requires three steps. First, the CO2 must be separated from other gases. Many industrial processes have been developed and proven in other industries to do this. The natural gas processing industry, for example, has developed systems for separating CO2 from methane.

Second, the CO2 must be transported by pipeline to the permeable rock underground. The oil and gas businesses already have substantial experience with moving compressed fluids through pipelines, so the transportation of CO2 can be readily accomplished.

Finally, the CO2 must be injected into a geologic formation that will retain it for millennia. Here again, we need not look farther than the oil business. They already use a process called enhanced oil recovery that involves injecting CO2 into oil reservoirs deep underground. The gas decreases the surface tension between oil and water in the reservoir, freeing up oil for extraction. Enhanced oil recovery has been an active process in the industry for the last 30 years and so could be improved upon for CO2 storage.

So, we know how to capture CO2, how to transport it, and how to inject it into geologic formations. But, how do we know that the CO2 will stay in these formations for millennia? The story here is a bit more mixed, but the reality is that the same two mechanisms that have kept natural gas from escaping from its reservoirs for geologic time will also trap CO2. Those two factors include capillary forces and the type of rock. Picture a straw in a glass of Coca-Cola. After you sip through the straw, you might notice that the carbonated soft drink gets trapped in the straw. A similar thing happens underground, where capillary forces keep buoyant fluids from escaping. Gas is also physically trapped inside porous rock by layers of solid rock overhead. Think of it as a lid on a jar.

The bottom line is that although the CO2 that is injected into terrestrial geologic formations is buoyant and can escape if the formation is not appropriately confined, it's well documented that sedimentary basins have retained many billions of tonnes of naturally occurring CO2 as well as trillions of tonnes of buoyant hydrocarbons for millions of years.

The only issue that remains is price. Nobody knows for certain how much all of this will cost because the integrated process of capturing, transporting and storing CO2 has not been estimated. It's generally expected, however, that capturing and storing CO2 from a coal-fired power plant will increase the electricity generation costs by less than 50 percent. Given that traditional coal-fired power is currently less than half the price of wind power and about a quarter the price of solar power, coal-fired power with CO2 capture and storage will still be cheaper than renewable power options.

Avoiding dangerously high levels of atmospheric CO2 requires drastic emissions reductions from the power industry. Carbon capture and storage is technologically viable, it's likely to be cheap compared to renewable energy options, and it capitalizes on an energy infrastructure that is already in place.

Now read an opposing view by Peter Montague, executive director of Environmental Research Foundation on page two.