Induced Earthquakes A Potential Hazard for Geological Storage of Carbon Dioxide

Summary.  The world is burning fossil fuels at an ever-increasing rate, resulting in increased release of the greenhouse gas carbon dioxide into the atmosphere.  This results in an increase in the long-term globally averaged temperature.  Consequently there is great interest in developing carbon capture and storage in geological repositories to help abate the increase in atmospheric carbon dioxide.

Zoback and Gorelick have just published a paper that a) emphasizes the vast amounts of carbon dioxide that need to be captured and stored, and b) analyzes in detail the likelihood that small-scale earthquakes may be induced at the injection sites because of the increased fluids introduced into the storage sites.  Their concern is that even small to medium scale earthquakes may destroy the integrity of the sites, leading to significant leakage of carbon dioxide back into the atmosphere.  They conclude that extensive deployment of carbon storage involves considerable risk.

Background.  Zoback and Gorelick have analyzed the long-term geological storage of carbon dioxide (CO₂) as a means of permanently removing this greenhouse gas from the atmosphere by carbon capture and storage (CCS; see the next section).  First we present some introductory information on CCS. (Background on CCS may be found in this earlier post.)

The European Union (EU) has embarked on the only multinational program in the world, based on binding enacted policies, to reduce emissions below the emissions levels of 1990 by 20% by 2020, and by 80-95% by 2050 (the EU Roadmap; see this post).  Achieving such goals requires decarbonization of most energy sources.  The EU recognizes that a major portion of this reduction should come from use of CCS for large scale fixed sources involved in generating electricity. 

To begin research and development of CCS technology, the EU has selected six demonstration projects in six member countries, using differing capture and sequestration technologies.  The EU has committed EUR1 billion (US$1.25 billion) to them.  Variously, they range in size from one at 30 MW (to be scaled up to over 300 MW) to 900 MW, with most projects expected to capture about 90% of the emitted CO₂.  Storage will be in land-based or offshore saline aquifers, and depleted land-based or offshore gas fields.

In the U. S. the state of California is implementing a plan very similar to the EU’s Roadmap.  In a non-official report detailing how California might attain these goals, the California Science and Technology Council (CSTC) relies heavily on decarbonizing energy sources to the greatest extent possible (see this earlier post).  Electricity generation is to be decarbonized, to the extent that use of fossil fuels is maintained, by use of industrial-scale CCS, even though the report recognizes that this technology remains unproven.  Decarbonization of electricity generation is especially important because CSTC envisions use of electric vehicles to decarbonize transportation.

The U. S. Department of Energy (DOE) is sponsoring research on CCS, as reported in the Carbon SequestrationProgram: Technology Program Plan of the National Energy Technology Laboratory.  Its budget request for Fiscal Year 2011 was about US$140 million, with anticipated sharing by an equal amount from Regional Carbon Sequestration Partnerships with universities and corporations.  This budget has grown from about US$10 million in 2000.  Recent support from the American Recovery and Reinvestment Act of 2009 (the fiscal “stimulus”), included in the recent growth of this funding, is essentially exhausted at this time. All aspects of the various stages in capture, release and concentration, transportation and geological storage, as well as monitoring, verification and accounting, are being investigated at laboratory and small pilot scale.

Similar programs are also supported in the DOE Fossil Energy program.  Their requested budget for Fiscal Year 2013 is about US$276 million for CCS and Power Systems, which supports projects as large as industrial scale pilot projects.

Cautionary Analysis of CCS.  Zoback and Gorelick analyzed the dangers to maintenance of reservoir integrity in geological sequestration of CO₂, in a paper published in the Proceedings of the National Academy of Sciences, June 26, 2012, vol. 109, pp. 10164-10168 .  As background, the authors note:

·        CCS will be very costly;

·        in the U. S. use of coal for generating electricity produces about 2.1 billion metric tons of CO₂ a year, or about 36% of all U. S. emissions;

·        China’s emissions are about 3 times more than this from coal-fired generation, corresponding to about 80% of its emission rate;

·        annually, on a worldwide basis, CCS has to contend with 3.5 billion tons of CO₂, which requires injecting an amount of CO₂ underground roughly equal to the volume of all the oil extracted from oil wells worldwide;

·        this amount of injected CO₂ requires that worldwide about 3,500 functional industrial-scale injection facilities be operational by mid-century, averaged to about 85 facilities added per year; and

·        geological storage must remain faultlessly leak-tight in order to compare with freedom from emissions of renewable energy sources.

The authors include the following analyses:

o       The paper itemizes several instances of earthquakes apparently triggered by underground injection of liquids.  This can arise because many geological formations are already in states of unresolved stress, so that the relatively minor perturbation arising from fluid injection releases the stress in an earthquake.  The fluid in essence makes it easier for the stressed surfaces to slide over one another, which is the hallmark of an earthquake.  Zoback and Gorelick emphasize that it is not any land-based earthquake damage to human wellbeing that concerns them, but rather that even small earthquakes, likely not to produce damage to structures, are likely to damage the geological structures holding the pressurized CO₂.  CO₂ could then readily permeate to or near the surface, permitting release into the atmosphere and defeating the intent of the storage in the first place.  They present the results of calculations that even a small earthquake of Magnitude 4 could induce slippage of several cm. along a fault of about 1-4 km (0.6-2.4 mi).

o       In stressed geological formations, it is not only the pressure of injected CO₂ that is potentially hazardous, but also the rate of injection.  More rapid pressure buildup is more likely to trigger an earthquake event; the need to dispose of large volumes of CO₂ would be an incentive for high injection rates.

o       A widely known injection site is the Utsira formation of the Sleipner gas field in the North Sea.  About 1 million tons of CO₂ has been separated from natural gas and reinjected below ground every year, for the past 15 years.  There has been no earthquake activity to date.  The authors calculate that about 3,500 such sites would have to be identified and put into service to accommodate storage needs projected for 2050 (most of which would be needed right now, in fact).  The authors conclude “Clearly this is an extraordinarily difficult, if not impossible task” if only geologically suitable sites are to be used.

o       Depleted oil and gas wells, while seemingly attractive as potential injection sites, are not numerous enough to satisfy the need, and are not necessarily located conveniently for the need.

The authors conclude “multiple lines of evidence indicate that preexisting faults found in brittle rocks almost everywhere in the earth’s crust are subject to failure, often in response to very small increases in pore pressure. In light of the risk posed to a CO₂ repository by even small- to moderate-sized earthquakes, formations suitable for large-scale injection of CO₂ must be carefully chosen.”  Because of the extremely large volumes of CO₂ needing to be disposed of, the industrial-scale CCS needed will be “extremely expensive and risky for achieving significant reductions in greenhouse gas emissions”.

Certain CCS projects have been abandoned due to risk and lack of financing.  The very factors identified by Zoback and Gorelick are echoed in these two recent news reports. 

The Guardian on June 17, 2012 reported that Ian Marchant, chief executive of Scottish and Southern Energy, while still favoring CCS development, warned the British Parliament that a CCS project his company is undertaking is “the most risky project I’ll ever invest in….CCS is…at the demonstration stage….We do not know that this technology will work”.  He called for UK government support at this demonstration phase of the project.

The same article noted that another company, Scottish Power, abandoned CCS technology last year.  Together with Shell, the company evaluated it would need at least £1.5 billion (US$2.3 billion), and the UK government could not support such a funding level.

Similarly, theGuardian reported on June 26, 2012 that Ayrshire Power (Scotland) abandoned its planned new CCS-fitted 1852 MW power plant because it feared it could not obtain funding from the UK and the European Commission.  Nevertheless, the Scottish energy minister still strongly supports CCS development since it borders North Sea offshore CO₂ storage sites.

Rebuttals of Zoback and Gorelick’s warnings.  There has been response from the CCS community rebutting the serious concerns expressed by Zoback and Gorelick.  For example, two scientists were featured in the internet-based Carbon CaptureJournal (accessed June 27, 2012).

Dr. Malcolm Wilson, Chief Executive Officer, The Petroleum Technology Research Centre (PTRC), provided a detailed accounting of the experience gained at the Weyburn-Midale Project, an oil field storage development project in Saskatchewan, Canada, which it seems is an extended oil recovery project as well.  Storage has been under way there for 11 years, with a total of 21 million tonnes (metric tons) of CO₂ stored in that time.  Detailed research and characterization of the site has been undertaken throughout this time; indeed, seismic events with Magnitudes of -1 (extremely small) have been recorded.  Dr. Wilson considers this site now to be industrial scale, as 2.8 million tonnes of new CO₂, and more than 5 million tonnes when recycled CO₂ are included, have been injected; no earthquake activity or leakage has been identified.

PTRC is also conducting research on their Aquistore Project, for storage in saline aquifers.  Noting with approval that Zoback and Gorelick cite aquifers favorably because of their very large storage capacities, Dr. Wilson notes that the Aquistore Project will be the first industrial scale storage project, since it will receive CO₂ from a coal-fired power plant.

Dr. Bruce Hill, senior staff geologist at Clean Air Task Force (CATF) rebuts the concern over lack of integrity of storage sites due to earthquake activity by emphasizing the rate of CO₂ migration toward the surface, rather than the total amounts potentially released.  Dr. Hill emphasizes that there are many layers of rock structures, extending thousands of feet, overlaying injection sites, seeming to belittle the concerns of Zoback and Gorelick.  Dr. Hill feels that the examples cited by the authors are not representative.  He points out that “approximately 1 billion tons of CO₂ have been safely injected (and stored) in the process of enhanced oil recovery 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”.

Dr. Hill concludes that CCS technology is “viable” and should play a significant role in potentially storing the very large amounts of CO₂ that need to be recovered to reduce atmospheric CO₂ accumulation.

George Peridas responded to the paper on the Natural Resources Defense Council Blog on June 22, 2012.  Mr. Peridas believes that Zoback and Gorelick raise valid issues, including whether CCS can cause earthquakes and whether such earthquakes could lead to leakage of the injected CO₂.  But in his opinion, the conclusions reached by the authors are more extensive than warranted by the evidence, for example with respect to the second issue, leakage.  He does not agree that an earthquake event would lead to migration of CO₂ all the way to the surface.  He believes that an experiment cited by the authors, performed on granite, a brittle mineral, is not representative of capstone layers anticipated in CCS, which would be more compliant, yet impermeable, shales.  In the case of existing fossil fuel geological reservoirs, large earthquakes have been known to occur without loss of the materials.  Mr. Peridas additionally cites Sally Benson (Stanford University and Lead Coordinating Author of the Underground Geological Storage Chapter in the Intergovernmental Panel on Climate Change Special Report on CCS) as stating that naturally care must be taken in choosing CCS injection sites, but that finding such sites should be feasible.

Discussion

Our earlier post, “Carbon Capture and Storage: A Needed yet Unproven Technology”, presented background information on the various technologies that may be employed in each phase of capturing CO₂, from the burning of fossil fuels for energy, to transporting the CO₂ to a storage site, and finally the actual storage process.   Many problems remain to make CCS industrially viable for utility-scale facilities.  Resolving these problems requires investment of large sums of money, worldwide, to arrive at practical CCS by about 2020.  Currently a relatively small number of demonstration and pilot projects are under way around the world.

The use of fossil fuels is projected to grow considerably in the coming decades around the globe, primarily in developing countries which will power their rapidly expanding economies with energy derived from burning fossil fuels.  This means that the annual rate of CO₂ emissions will continue expanding, and that the total accumulated concentration of atmospheric CO₂ likewise will continue increasing.  Even in developed countries having programs to abate CO₂ emissions at various stages of maturity, a major aspect of such abatement involves shifting transportation to electric power.  Thus the total demand for electricity is projected to grow in developed countries as well; to the extent that this demand is not met by renewable sources the need for contending with abatement of CO₂ emissions likewise will grow.  For this reason emission abatement programs will rely ever more heavily on technologies such as CCS.

The paper by Zoback and Gorelick serves at least three useful functions.  First, by arithmetic analysis, it underscores the vast, unprecedented need for functional and effective injection sites projected by 2050.  Some of this information has been summarized above.

Second, its geophysical modeling emphasizes the many unknown factors remaining in choosing and developing new CO₂ injection sites.  The seals installed surrounding well bores, and the many geological factors involved in retaining the injected CO₂ out of contact with the atmosphere for hundreds or thousands of years must be essentially fail-safe.  Yet this work emphasizes that the very act of injecting pressurized fluid facilitates potential small-scale earthquakes that, according to the modeling, have the potential of opening fissures in these seals that could lead CO₂ back to the surface.

Third, it has engendered fruitful debate in the CCS community about the integrity of proposed injection sites.  Although these issues were already known among workers in the community, they have now been aired among a wider public.  This has the effect of ensuring that research and data gathering, involved in characterizing new injection sites, will be carried out diligently and effectively so that wise siting choices may be made.

The critics of Zoback and Gorelick, such as those cited above, include examples in their rebuttals of injection sites taking advantage of pre-existing wells used in the extraction of oil and gas from their geological repositories.  These have kept the fuels underground for millions of years, and so are cited as justifying CO₂ injection for the same reasons.  These are likely not representative of the thousands of new storage injection projects that will be needed to accommodate the demand.  Overall the number of pilot injection sites worldwide is small, and many are new experimental projects.  The concerns raised by Zoback and Gorelick merit careful attention going forward as CCS technology is developed further and deployed in number.

© 2012 Henry Auer