Seismic Risk Won’t Threaten the Viability of Geologic Carbon Storage
This week’s rumblings against carbon capture and storage (CCS) as a powerful means to mitigate global climate change come not from any natural geological source, but solely from an opinion piece published in this week’s Proceedings of the National Academy of Science (PNAS) Perspectives. Despite the arguments of two Stanford geophysicists, however, there is plenty of countervailing scientific evidence that CO2 from U.S. fossil power plants can be captured and safely stored. While the opinion piece rightly raises the importance of rigorous site selection and site characterization for commercial scale storage, it falls far short in its analysis of the overall feasibility of storing commercial volumes of CO2. Here’s why:
By analogy with recently experienced earthquakes resulting from brine injections, the authors attempt to cast doubt on the feasibility of large-scale geologic storage of carbon dioxide captured from industrial sources by pointing to the role of CO2 pressure buildup in the hosting formations in their potential to induce earthquakes and resulting fractures and faults. Their concern is not about the impacts of tremors nor large scale earthquakes that would let CO2 rush out, but instead, about the possibility that the induced seismicity could be accompanied by small scale fracturing that could migrate upwards and compromise the integrity of an overlying geologic seal.
What the article does not say is that for a brittle fault or fracture zone to reach the surface it would take crossing thousands of feet of rock and shale layers that may very well, in the process, accommodate the upwardly propagating stress like a plastic substance bending like taffy –instead of fracturing. It also does not address the rate at which any CO2 affected by such small scale fracturing might migrate over time, and whether those volumes would be significant over the time scales necessary to combat global warming. Moreover, according to MIT geoscientist Ruben Juanes, there are no models or data that can predict seismicity from large-scale CO2 injections. Furthermore, CO2 injection technology is hardly new. Approximately 1 billion tons of CO2 have been safely injected (and stored) in the process of enhanced oil recovery (EOR) in the U.S. since the late 1970s, with no reported seismic incidents. In fact, there have been no earthquakes reported anywhere from saline CO2 injections either, according to the June 15 NAS report (Induced Seismicity Potential in Energy Technologies).
In the opinion piece, the authors paint, with a broad brush, a scenario of limited storage capacity for power plant CO2 generated in the Midwest’s Illinois Basin–the U.S. locus of coal power generation. In their rush to judgment, the authors overlook numerous storage strategies that would complement local and regional storage in the Midwest:
- Their contention is based on the unrepresentative example of the AEP Mountaineer pilot CCS project in West Virginia, combined with computer modeling of the Illinois basin done in 2009 by Lawrence Berkeley National Laboratory undertaken for a purpose other than to predict seismicity. The poor injectivity encountered in the Mountaineer project is not representative of the geology of the Mt. Simon Formation across the entire Illinois Basin. A better example is the continuing success at the ADM project underway presently in Decatur, Illinois.
- An understanding of the three-dimensional subsurface geology is critical. In the Illinois Basin, there are other formations that have the potential to simultaneously store CO2. The University of Texas Bureau of Economic Geology Gulf Coast Carbon Center, has been investigating stacked storage in combination with EOR in brine formations below producing zones in Mississippi. Tight formations with low permeability and multiple seals above the Mount Simon Formation provide an additional layer of security.
- Carbon dioxide can and will be pipelined to the Gulf Coast and Texas’ Permian Basin for enhanced oil recovery. Plans are underway for an extension CO2 pipeline that will extend Denbury Resources’ existing “Green Pipeline” up into southern Illinois to tap into anthropogenic sources of CO2. A 2011 NETL study suggests next-generation EOR in depleted US oilfields can accommodate an additional 20 billion tons of CO2.
- Pipelines could also carry CO2 to other formations in the offshore Gulf, Atlantic and Pacific Coasts where there are an estimated 500 billion to 7.5 trillion tons of storage capacity, according to DOE.
- CO2 pipeline build-out has been studied by the research group Battelle for several international climate mitigation scenarios and suggests that the pace would be reasonable. ARI, an energy resources consulting firm, estimates that three 800-mile pipelines could accommodate the CO2 from Midwest power plants for 30 years.
- Brine water production and reinjection into other formations can relieve formation pressures that could potentially lead to rock failure.
Taken together, the weight of evidence suggests that CCS technology is viable and that a combination of storage options will provide capacity for large volumes of captured CO2. Whether all the carbon dioxide emitted by industrial activities in the U.S. and around the world can be captured and stored remains to be seen, but CCS is viable and has an essential and important role to play in reducing greenhouse gases. With numerous small-scale CO2 injections and four decades of EOR under our belt, now is the time to invest in the understanding of large-scale geologic storage, rather than abandon it.