We still need even better clean coal technology, but when it comes to reducing carbon emissions, the overriding research question is geological. No clean coal technology can forestall climate change without the aid of carbon dioxide sequestration. Unless the carbon dioxide from coal-fired plants is permanently stored somewhere, it will go into the atmosphere and worsen global warming. Sequestration proposals include pumping carbon dioxide underground, pumping it under the sea, and mineralizing it for burial. But significantly reducing carbon emissions while still increasing fossil fuel consumption will require a massive effort: liquid carbon dioxide would have to be sequestered on the same general scale on which the original fossil fuel sources were removed. It’s a staggering proposition.
To date, pumping carbon dioxide underground has mainly been a way to push more oil to the surface; the primary objective wasn’t really to store carbon dioxide permanently. So a critical question remains unanswered: will carbon dioxide stay where you want it?
In an old steel-walled lab at Los Alamos National Laboratory in New Mexico, geochemist George Guthrie holds out a smooth chunk of cement the size of a sea scallop. The chunk was recently drilled out of cement poured more than 50 years ago to plug the pipe in an old Texas oil well that had been crammed with carbon dioxide to enhance oil recovery. Guthrie holds up the chunk: a quarter-inch swath of it is the color of an orange Creamsicle. This staining, Guthrie says, is acid corrosion induced by carbon dioxide, which forms carbonic acid when it mixes with groundwater.
The chunk is a kind of Rorschach test. On the one hand, it could be read to imply that the carbon dioxide damaged the cement plug. On the other hand, it might imply that the damage was minimal – and may not progress further. There’s a lot riding on the answer. If the plug on a reservoir blew, the carbon dioxide could be released – and the climate benefits of sequestration would, as it were, vanish into thin air. “There are significant consequences for doing this wrong,” Guthrie observes. “On the other hand, it may be that much of the technology for doing this right already exists. There has been such enthusiasm behind [sequestration] that it is easy to forget about the implications of doing this on such a large scale.”