Does Carbon Sequestration Work?
I mentioned in the previous post that while I do see an important role for renewable energy sources, I don’t see fossil fuels going away entirely anytime soon. While putting a price on carbon is likely to shift some electricity generation from coal to natural gas (a topic on which I’ll have much more to say later), the electricity generation infrastructure in the US today is very much set up for a substantial amount of coal, so even if coal gets more expensive with the cost of carbon included in it there will still be a fair amount of it in use.
In practice, what that means is that for the US to have any hopes of meeting the emissions reduction targets that a cap-and-trade system would require coal plants are going to need to implement carbon capture and sequestration (CCS) technology on a large scale. There are various ways this could be done, some of which involve using the carbon dioxide captured from emissions and using it to aid in oil and gas drilling or for other purposes, and some of which just involve pumping it underground and hoping it stays there.
One of the major questions about geological sequestration, however, is whether it will actually work. Can carbon dioxide really be kept underground without escaping for the very long periods (on the order of centuries) necessary to stabilize the climate? A 2007 paper in the journal Energy looked at exactly this issue and concluded that it can.
The paper looked specifically at the emissions of carbon dioxide from various geological contexts to see what implications they had for geological storage of carbon. In general, they found that geological reservoirs in areas of primarily sedimentary character are quite stable and can often trap gases for millions of years. Depleted natural gas reservoirs are particularly suitable for carbon storage, since the fact that they held the natural gas until it was extracted clearly shows that they can securely hold gases. The main risk in this sort of thing is a well blowout, since injecting the carbon into the reservoir would require opening up a potential path for it to escape. In the case of depleted gas reservoirs, the wells used to extract the gas also have this risk. This risk is real and hard to quantify, but the paper’s authors conclude that it can largely be overcome by careful design of the injection wells and the techniques for capping them. The few existing pilot projects for carbon sequestration have shown little or no release of carbon.
Importantly, the paper shows that geological sequestration should not be attempted in areas of primarily igneous nature, as the effects of active volcanism create a much larger risk of carbon escaping than in sedimentary areas, where natural releases of carbon dioxide tend to be limited to small clusters of carbonated springs. Most spectacularly risky are highly stratified lakes in tropical areas known for igneous activity. These lakes are potentially subject to sudden, violent releases of carbon dioxide that in a few notorious cases have suffocated large numbers of people. The most deadly example occurred at Lake Nyos in Cameroon in 1986, where 1700 people were killed. Carbon dioxide is often described as not being a threat to human health, and under ordinary circumstances it isn’t, but when it completely displaces all of the air in a confined area it leads to suffocation by preventing the body from receiving oxygen.
With the first pilot CCS system at a US coal plant opening in West Virginia, now is a good time to be looking the still largely untested potential for geological storage of carbon. One advantage of putting this sort of system in coal-rich areas, in addition to the convenience for plant operators, is that they are by definition the sort of sedimentary areas that are likely to be the most stable sites for underground sequestration efforts. Of course, it’s hard to say how this will ultimately pan out, but it’s definitely worth watching.
HOLLOWAY, S., PEARCE, J., HARDS, V., OHSUMI, T., & GALE, J. (2007). Natural emissions of CO2 from the geosphere and their bearing on the geological storage of carbon dioxide Energy, 32 (7), 1194-1201 DOI: 10.1016/j.energy.2006.09.001