The geological plausibility of CCS


in Politics, Science, The environment

Andrea Simms-Karp and a stone wall

Two articles on the April 2nd issue of Nature look into some of the physics, chemistry, and geology associated with carbon capture and storage (CCS) as a possible form of greenhouse gas mitigation. The first largely summarizes the results of the second. Each stresses how significant amounts of carbon dioxide (CO2) are already trapped in groundwater in the subsurface environment, suggesting that the artificial addition of more may be safe and effective. Leaks are avoided due to the “presence of sealing, low-permeability rock formations above the targeted layer,” such as those found above natural gas fields. The article considers CO2-rich natural gas fields in North America, China and Europe as natural analogs for future CCS sites. It concludes that relatively little (about 10%) of the CO2 gets incorporated into rocks, from which it is unlikely to escape. Most remains in water, from which future emissions are more possible. It concludes that the hydrogeological characteristics of future CCS sites will need to be carefully considered, bearing in mind that most of the CO2 will apparently end up saturated in water.

None of this provides definitive support for CCS as a mitigation option. Rather, it provides some guidance into the further research necessary to determine if it can be safe and environmentally effective. Notably, this research also gives no consideration to the economics of CCS deployment, nor to the timelines across which it can be achieved. Indeed, these articles could be taken as evidence of the relative infancy of the scientific consideration of subsurface disposal of carbon dioxide, something that governments assuming its near-term commercial viability should note.

{ 2 comments… read them below or add one }

R.K. April 2, 2009 at 2:48 pm

One factor that differentiates CCS sites from natural deposits is that the former will need artificial wells drilled into them.

Over thousands of years, that seems likely to increase the probability of a leak.

. September 22, 2012 at 8:51 pm

Carbon capture and storage

SIR – You were correct in saying that the enormous cost of the geological sequestration of carbon dioxide is a major impediment to its implementation (“Going underground”, August 18th). However, your article contains some important factual and conceptual misrepresentations. For example, it concludes: “Ultimately…the safety risks are a secondary issue. The technique will be successful only if the cost of hiding a tonne of carbon underground falls lower than the cost of emitting a tonne into the air.” We strongly disagree.

Safety risks are paramount, especially if geological sequestration of CO2 was cheap enough to be widely adopted. A recent report from the National Research Council on seismic risks associated with energy technologies pointed to the potential for large earthquakes to be associated with carbon sequestration. In our recent article in the Proceedings of the National Academy of Sciences we argued that even relatively small quakes could damage the caprock seal enough to release the CO2 back into the atmosphere.

Although we argued that such leakage could negate the desired emission reductions, we never said that if leakage were sudden it might kill people, as implied in your article.

Mark Zoback
Steven Gorelick
Stanford University
Stanford, California

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