SENATORS CONCERNED AFTER TWO STUDIES LINK CCS WITH INDUCED SEISMIC EVENTS

Tamar Hallerman
GHG Monitor
06/22/12

Senators this week asked whether the federal government should continue funding large-scale carbon capture and storage projects days after a pair of reports concluded that the technology may have the potential to induce significant seismic events. At a June 19 hearing, members of the Senate Energy and Natural Resources Committee were concerned about results of the two new studies, which both linked the injection of CO2 into the subsurface and the potential for seismic events. “With this information that we now have, do you think it is perhaps premature or unwise to provide liability protection for CCS operatives? Can we even do this?” Ranking Member Lisa Murkowski (R-Alaska) asked Murray Hitzman, professor of economic geology at the Colorado School of the Mines and chair of the committee behind a National Research Council report on the topic released June 15. “Do you have thoughts as to whether it makes sense for the Department of Energy or federal government to be encouraging some of these large-scale demonstration projects? Or do you think it’s essentially a non-starter and that we should really look elsewhere to solve the long-term climate change issue?” Committee Chairman Jeff Bingaman (D-N.M.) asked Mark Zoback, a professor of geophysics at Stanford University and author of an article on induced seismicity published this week in the journal Proceedings of the National Academy of Sciences.

Geologists have studied induced seismicity as related to energy production for decades; practically any subsurface injection of fluid prompts small seismic events, researchers say. However, most of those events are small enough—less than 3.0 on the Richter scale—that they cannot be felt by people. While no seismic events have caused loss of life or significant property damage in the United States, earthquakes in Arkansas, Ohio and Texas stemming from wastewater injection operations over the last two years have led to heightened public attention and have raised some concerns about the potential for inducing additional events through energy technologies. As a result, Bingaman commissioned the National Research Council study in 2010 to look into the issue.

NRC Report Assesses Seismicity Potential of Several Technologies

Senators questioned witnesses about the results of the peer-reviewed National Research Council study, which concluded that CCS “may” have the potential for causing “significant induced seismicity.” Hitzman chaired a committee of 10 experts from academia and the private sector that examined the likelihood of CCS and other technologies like enhanced oil recovery, hydraulic fracturing, wastewater injection and geothermal energy development of inducing seismic activities. The committee gauged each technology’s history of inducing seismic activity by examining peer-reviewed literature, government documents, media reports and conducting informational meetings on the different technologies.

Overall, the committee concluded that while the risk of inducing earthquakes from processes like hydraulic fracturing and oil and geothermal production is fairly low, CCS and wastewater injection likely have a higher potential to prompt such events because both technologies inject liquids into the subsurface but do not subsequently withdraw fluid from its wells in order to balance pore pressure levels. That reality keeps pressure levels high, which can lead to an increased chance of earthquakes, the report says. In his testimony before the committee, Hitzman said that because CCS involves the continuous injection of CO2 into the subsurface at a high pressure for long periods of time, the technology has a particularly high potential for spurring seismic events compared to many other energy technologies. “Given that the potential magnitude of induced seismic events correlates strongly with the fault rupture area, which in turn relates to the magnitude of pore pressure change and the rock volume in which it exists, the committee determined that large-scale CCS may have the potential for causing significant induced seismicity,” he said.

The NRC study lists the net balance of fluid injected and removed from the subsurface as the most important factor in determining the potential of energy technologies to induce seismic events. While conventional oil and gas operations withdraw fluids from their production wells in the form of their respective commodities, ultimately helping decrease pore pressure and limiting any potential seismicity issues, CCS operations continually inject large amounts of supercritical CO2 underground for a period of years, the study says. Other factors also impact the probability of induced seismicity to a smaller extent, according to the study, including: rate of injection or extraction; volume and temperature of injected or extracted fluids; permeability of the relevant geologic layers; faults and fault properties; crustal stress conditions; the distance from the injection point and the length of time during which injection or withdrawal takes place.

While the study concludes that CCS operations could induce seismic events, it also emphases that risk is “currently difficult to accurately assess” given that there is not much field data available on the technology. The committee says that volumes injected so far as part of pilot-scale CCS projects worldwide have not been able to provide the data at scale needed for conclusions to be made on future large-scale demonstration projects and their potential to induce seismic events. In his testimony, Hitzman said that more research should be conducted in order to more properly gauge the CCS’ effect. The report also recommends developing industry best practices and conducting thorough characterization work on potential sites, among other suggestions.

Stanford Paper Takes Harder Line

The other paper examined by the Senate Energy Committee this week comes to a similar conclusion about CCS but takes a harder line in terms of its language. In their short ‘Perspective’ article published in the journal Proceedings of the National Academy of Sciences, Stanford geophysicists Mark Zoback and Steven Gorelick conclude that there is a “high probability” that small to moderate-sized earthquakes will be triggered by the injection of large volumes of CO2 into the brittle rocks commonly found in the country’s continental interiors, often considered ideal sites for long-term CO2 storage. “Modern seismic networks have shown that earthquakes occur nearly everywhere in continental interiors… The occurrence of these earthquakes means that nearly everywhere in continental interiors a subset of the preexisting faults in the crust is potentially active in the current stress field… Because of the critically stressed nature of the crust, fluid injection in deep wells can trigger earthquakes when the injection increases pore pressure in the vicinity of preexisting potentially active faults,” according to the article. The paper says that those fine fault lines are so small that they can sometimes be missed during a project’s characterization phase, according to the article, helping make the case for careful site characterization and thorough monitoring. “In the context of a critically stressed crust, slip on preexisting, unidentified faults could trigger small- to moderate-sized earthquakes at pressures far below that at which hydraulic fractures would form,” the report says.

Zoback and Gorelick argue that while induced seismicity stemming from CCS operations is of worry, even more principal a concern is that those small to medium-sized quakes generated could threaten the seal integrity of the CO2 storage formation. “Because even small- to moderate-sized earthquakes threaten the seal integrity of CO2 repositories, in this context, large-scale CCS is a risky, and likely unsuccessful, strategy for significantly reducing greenhouse gas emissions,” the paper says. Like the NRC study, the article says that pilot-scale tests so far have not come up with enough data to gauge seismicity and that more is needed.

CCS Proponents Prep Responses

Meanwhile, some CCS proponents began preparing rebuttals to the two studies this week, particularly to the Stanford article. “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,” said Bruce Hill, a senior geologist at the Clean Air Task Force, in his response to the Stanford paper. In particular, Hill said the piece ignores the results from the roughly 1 billion tons of CO2 that has been injected to the subsurface as part of EOR operations over the last 40 years, with no reported seismic incidents.

Hill also said that the study’s focus on small-scale fracturing, which the authors said could compromise the integrity of a geologic seal, is overblown. “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,” he said. “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.” Other organizations supportive of CCS said they are preparing responses to the reports that will likely be released soon.

Over the last several years, industry has also developed its own recommendations for minimizing the risk of inducing large seismic events, GHG Monitor previously reported (Vol. 7, Issue 3), most adhering to the mantra of extensive site characterization. “You have to do a very, very diligent job of characterizing the rocks before you inject. And that’s not just running some well logs. You need to understand the geomechanical environment of those rocks,” Julio Friedmann, chief energy technologist at Lawrence Livermore National Laboratory, previously told GHG Monitor. “The other thing you need to do is modeling simulation to understand what the likely failure envelopes are.” Keeping a close watch on injection rates, as well as spacing out wells across a field (instead of injecting via a single well) are also widely considered ways to help lessen any potential induced seismicity impact.

‘Changing the Dialogue’ on CCS

Following the hearing this week, Bingaman said that the discussion of the induced seismicity issue is “important and timely.” “I think [the witnesses] raised a lot of questions about all the different types of injection that is taking place, particularly wastewater injection and CCS,” he told reporters on the sidelines of the hearing, adding that he does not yet see a clear path forward for how or whether the issue should be addressed in Congress.

In his testimony, Zoback said that he is looking to “change the dialogue” surrounding CCS with his paper. “What we’re trying to do is change the dialogue and ask people to consider this question [of whether to pursue CCS] not just in context of scale and the cost, which have been raised by many people in the past, but also in the context of 10, 20 years from now when these moderate-sized earthquakes occur in one of the repositories, what is that going to mean for this strategy that we’ve embarked on?” he said. “This needs to be thought through very carefully.”