Geologic Carbon Sequestration Frequently Asked Questions
Protecting Human Health and the Environment
1. How Can We Trust That Geologic Sequestration Will Be Safe Now and in the Future?
2. What Does It Mean to Do Field Tests and Why Do You Need to Do Them?
3. Will Injecting Carbon Dioxide in the Ground Send Other Chemicals to the Surface?
4. What Are The Possible Effects of High Exposure of Carbon Dioxide to Animals or Humans?
5. What about Today’s Problems? How Does Sequestration Reduce Current Negative Impacts of Coal Burning, Such as Asthma in Kids?
6. Does Storage of Carbon Dioxide Underground Bring With It a Risk of Contaminating Drinking Water Supplies?
Ensuring the Integrity of Sequestered Carbon Dioxide Reservoirs
1. How Do You Know That Carbon Dioxide Injected into the Ground Will Stay There?
2. What Happens if Injected Carbon Dioxide Leaks?
3. What Is A Geologic “Seal” and How Can We Be Sure That Geologic Seals Will Hold?
4. Could Carbon Dioxide from a Nearby Geologic Sequestration Site Leak into My Basement?
5. What Will Happen to Sequestered Carbon Dioxide if there Is Seismic Activity Nearby?
6. Who Regulates Carbon Sequestration?
7. How Does Carbon Dioxide That Is Injected Underground Stay There?
Effectively Managing Field-Testing Operations
1. How Are You Going to Decide Where to Do Field-Testing?
2. Why Go to All This Trouble Now if Climate Change Isn’t Supposed to Happen for 100 Years?
3. What Alternatives Did You Consider in Addition to Carbon Sequestration?
1. How Can We Trust That Geologic Sequestration Will Be Safe Now and in the Future? Geologic Sequestration is the storage of carbon dioxide in deep underground rock formations. These formations can include depleted oil and gas reservoirs, coal seams that are too deep or too thin to be mined economically, and formations of water that are far too salty and too deep to be used for drinking water or any other purpose. These formations are known to have safely held naturally occurring pockets of carbon dioxide for millions of years, and they have the potential to safely hold man-made carbon dioxide as well.
The oil industry has been safely injecting carbon dioxide into mature oil fields for over 30 years with an exemplary safety record. The carbon dioxide is injected to re-pressurize old wells in order to enhance recovery of oil and gas. There has never been an accident or safety problem related to these operations. With advanced drilling techniques, engineering, and analysis available today, that safety record should continue in the future. And, scientists are continuing to improve the techniques for injecting the gas to do so even more safely. Scientists are also developing ways to better understand how carbon dioxide moves within deep rock formations. This information will be used to test and develop models to predict what will happen to the injected carbon dioxide and monitoring and verification equipment installed at each site is used to make sure the gas behaves as predicted and to detect any leaks if they do occur. 2. What Does It Mean to Do Field-Tests and Why Do You Need to Do Them?
There is an old saying: “measure twice, cut once” which is a way of saying, make sure something will work before you commit to it. That’s what field testing is about. Scientists are pulling together a lot of information which suggests that carbon dioxide can be injected into geologic formations and stored virtually indefinitely. Yet it really has not been done in a large way, so before committing to this technology and the expense of building facilities, field-testing will be used to make sure it works and to perfect the methods used for injection, monitoring and long-term management of storage facilities.
Field-testing involves starting with small-scale tests under controlled and well-understood conditions and then increasing the size and complication of those tests in order to scale up to real-life conditions. The initial field-tests will be conducted in formations that are well mapped and well understood by scientists – and in locations or under conditions where they cannot harm humans or the environment even if the worst happens. As the tests show which techniques work, those techniques will be tested at increasingly larger scale, with safeguards to ensure they will not harm humans or the environment, in order to determine whether and how it can be used at large-scale.
As an analogy, even a powered model airplane can demonstrate the principles of flight and steering used in a Boeing 747. Yet there were several levels of planes developed and tested before large jets were used for commercial flight. In the same way, field-tests of carbon sequestration will both determine if it works and will help scientists to determine the safeguards necessary to protect the public and the environment.
3. Will Injecting Carbon Dioxide in the Ground Send Other Chemicals to the Surface? It is unlikely that injection will cause other chemicals to come to the surface. When carbon dioxide is injected into the ground it can have at least two effects. The first is that is increases pressure in the formation into which it is injected and the second is that it reacts with the deep salt water in formations into which is injected and can make that water more acidic. The increased pressure is not likely to send other chemicals to the surface and monitoring will be used to make sure this does not happen. The more acidic water can dissolve minerals, including heavy metals, from the surrounding rock formations and those dissolved minerals can migrate with the water through the rock formation. The watery mix is known as a plume. Scientists currently use monitoring to track the migration of plumes in groundwater. Sequestration sites will be selected because they are isolated from ground water by layers of dense rock. As a result, any dissolved carbon dioxide plume would not be able to seep into ground water. This same tracking should prevent other minerals dissolved in the salt water from migrating into ground water. If monitoring shows that a plume is getting to close to groundwater supplies then steps such as pumping can be used to prevent contamination.
4. What Are the Possible Effects of High Exposure of Carbon Dioxide to Animals or Humans? Carbon dioxide (CO2) is a natural gas in Earth’s atmosphere that is essential for plant life and survival of plants and animals. It is not toxic like Carbon monoxide (CO), and it does not pose a danger at the low levels in the atmosphere or the levels in our breath when we exhale. However, the air we breathe is a mixture of about 78% nitrogen, 21% oxygen and a very small percentage (less than about 1.5% total Argon, CO2 and other trace elements). If levels of CO2 in the air we breathe are elevated, it may mean that we are breathing less oxygen. This can cause headaches, dizziness, and similar side effects. At extremely high levels, exposure can cause unconsciousness, coma, or even death from asphyxiation.
There are a few cases where natural sources of carbon dioxide have leaked in a sudden rush, causing very high carbon dioxide levels in the air but usually it very quickly disperses in the air and poses no threat. Some geysers, like Crystal Geyser in Utah, are “powered” by pockets of naturally occurring carbon dioxide rather than geothermal energy. Such geysers erupt periodically, releasing trapped carbon dioxide which dissipates so quickly into the surrounding air that they are a tourist attraction rather than a source of danger. In a rare case in 1986, enough carbon dioxide was released at Lake Nyos in Cameroon that many people and animals in the surrounding valley suffocated to death. In that case, they determined that by putting a bubbler, like a water fountain, in the lake and running it all the time, they could prevent such a large release of naturally occurring carbon dioxide.
Safeguards include proper ventilation and protective gear for workers who handle carbon dioxide during carbon dioxide capture, transport and injection. Once injected, carbon dioxide will be monitored and the surrounding sites will include carbon dioxide monitors to determine if any leaks occur. If a leak is detected then ventilation and other methods could be used to prevent CO2 from accumulating at levels that could be harmful.
5. What About Today’s Air Pollution Problems? How Does Sequestration Reduce Current Negative Impacts of Coal Burning, Such as Asthma in Kids? The Department of Energy is funding research into ways to reduce other emissions from power plants, including mercury, sulfur dioxide (which causes acid rain), and small particles and soot that can exacerbate asthma. One of these technologies is called coal gasification, where the coal is turned into a gas, the impurities are stripped out, and the gas burns very cleanly and efficiently. This method also enhances the ability to capture carbon dioxide and inject it underground. The Carbon Sequestration Program will not have a direct impact on these pollutants, but it could work well with emerging technologies to improve the way we use coal and other fossil fuels.
6. Does Storage of Carbon Dioxide Underground Bring With It a Risk of Contaminating Drinking Water Supplies?
Research is focused on understanding and addressing the risks. It is important to understand that there are no natural connections between drinking water aquifers and potential carbon dioxide storage formations, because if there were, the brine or hydrocarbons in those formations would have already contaminated the drinking water over millions of years. There is a possibility that carbon dioxide, because of its buoyancy and low viscosity could escape where other fluids did not. These possibilities are well understood by geologists and the sites considered for carbon dioxide storage are those where there is virtually no chance of such a thing happening. Furthermore, the Carbon Sequestration Program is making a strong investment in technologies that can monitor carbon dioxide once it is injected underground and detect any movement. NETL is committed to researching the potential of carbon dioxide storage in geologic formations with no negative environmental consequences. Ensuring safety and environmental health is our top priority.
1. Will Sequestered Carbon Dioxide Leak and How Can You Detect It If It Does? There is no guarantee that carbon dioxide sequestered in underground geologic formations won’t leak. However, in the petroleum producing areas of the United States, oil and gas deposits, as well as naturally occurring carbon dioxide gas, have been trapped underground for millions of years. With proper construction and monitoring, there is a very high probability that these same formations will also prevent the significant leakage of carbon dioxide. Sites will be chosen carefully, and only the ones with the best geology will be picked for projects. The U.S. is also fortunate to have lots of experience storing natural gas, in which gas is injected underground during the summer and then recovered to heat homes in the winter. That experience can be applied to carbon sequestration as well. Carbon dioxide is a much safer, non-combustible gas compared to natural gas, which is used for heating homes, cooking, and home water heating. By understanding where natural gas storage has been safe and successful, we can apply that knowledge to carbon sequestration.
The rock formations chosen for carbon sequestration will normally be more than 2,000 to 2,500 feet underground. There is, of course, the remote possibility of an undetected fracture in the rock that could allow carbon dioxide to migrate upward toward the surface. However, even if this did happen, movement is expected to happen slowly because it takes a long time to move through all the different layers of rock. There are two kinds of leaks to be concerned about: large, rapid leaks and small, slow leaks.
When carbon dioxide is injected into geologic formations, it is injected into porous rock, like sandstone using best engineering practices. There are a variety of tests and mapping activities that are used before injection to determine that a site is acceptable for injection. Such testing should reveal if there are fractures in the cap rock and other faults that could provide an avenue for more rapid escape. Even if these are in the formation, the carbon dioxide would first need to seep out of the formation into the fault before migrating to the surface. Therefore, scientists are reasonably certain that large rapid leaks will not be a problem when best engineering practices are used in carbon dioxide injection.
The oil and gas industry has extensive knowledge of monitoring leaks of various gases from their wells. We can use the same technology that has been used by the underground gas storage and petroleum industries for over 50 years to check on the integrity of stored carbon dioxide. There are several methods that are used together: 1) monitoring for changes in the gas pressure in the site – a loss of pressure suggests a leak; 2) using “tracer gases” much like tracer bullets, that help scientists to detect where the gas is going; 3) looking for changes in soil composition that might suggest a leak; and, 4) using satellites designed to monitor for leaking gases. Modern engineering practices and the commercial experience of the oil and gas industry indicate that any significant leaks over a period of months, years, or decades are unlikely and that any such leaks that might occur can be managed so that they would not pose a significant risk to people or the environment.
This experience is less helpful in monitoring for small, slow leaks. There is some concern that such slow leaks could become a significant source of future atmospheric carbon dioxide loading over the course of a century. This is the subject of considerable ongoing research both to develop methods to monitor for such leaks and to mitigate those leaks if they occur.
2. What Happens If Injected Carbon Dioxide Leaks? Carbon dioxide occurs naturally in the environment, it is a big component of the air we exhale when we breathe and it is a by-product of burning fossil fuels - even of burning wood in your fireplace. One of the primary concerns about potential leaks is preventing the accumulation of CO2 at levels that could be harmful. This can be done in the short-term with increased ventilation.
If a leak is detected, the mitigation strategy will depend on the source and the nature of the leak. There are several options already and more are expected as a result of research and development underway. For example, if a leak is through the injection well, measures can be taken to repair the well. If the leak is through a fracture in the cap rock, measures such as pumping out the carbon dioxide to reduce the pressure in the reservoir can be used to prevent further leakage. If the field-testing of carbon dioxide sequestration or the practical experience with it shows that it cannot be stored in geologic formations over time, then other approaches to mitigating greenhouse gases will be need to be relied on more heavily. Additional research is underway to improve the methods for mitigating any potential leaks.
3. What Is a Geologic “Seal” and How Can We Be Sure That They Will Hold? The term ‘seal’ or ‘caprock’ refers to one or more layers of rock that separate the reservoir where carbon dioxide is injected from the surrounding formations, particularly freshwater zones near the surface. These layers prevent carbon dioxide and other fluids, such as the water in saline aquifers, from moving beyond the zone where they are injected. For example, a sandstone layer allows lots of movement of fluids among the pores between the sand particles, and is a good place to inject carbon dioxide. For the same reasons, sandstone is a bad seal. On the other hand, clay has very small pores, and is a very good seal, so you would want to inject the gas into a sandstone layer that was underneath a clay layer.
4. Could Carbon Dioxide from a Nearby Geologic Sequestration Site Leak into My Basement? It is unlikely that injected carbon dioxide will migrate to basements, especially at this stage of field-testing where smaller amounts of carbon dioxide are being injected and there is extra monitoring. That said, if a house were close to a sequestration site, there is a remote chance of this happening. Monitors, just like radon and carbon monoxide monitors from the hardware store could be used to check carbon dioxide levels. The first line of defense is selecting sites where this is not likely to happen and then using best engineering practices to ensure carbon dioxide is injected properly. Further, the use of underground monitoring and leak detection will be conducted at a depth that is much deeper than any basement, and in fact that is below drinking water supplies and groundwater levels. These actions should prevent injected carbon dioxide from seeping to the surface and accumulating in areas like basements.
5. What Will Happen to Sequestered Carbon Dioxide if there Is Seismic Activity Nearby? The impact of a seismic event on a geologic carbon dioxide storage site would depend on the magnitude and location of the event. It could cause the formation where the carbon dioxide is stored to break apart, which could change the interaction between the carbon dioxide and surrounding rock, water and minerals. It could also cause the carbon dioxide to leak. However, careful site selection should reduce to an absolute minimum the chance of sequestering carbon dioxide near areas of seismic activity.
6. Who Regulates Carbon Sequestration? Currently, sequestration projects must obtain environmental permits on a case-by-case situation. However, the U.S. Environmental Protection Agency has regulations for gases injected by pipelines, and is reviewing those and other laws to see how best to ensure the safety of sequestration projects. In addition, the National Environmental Policy Act (NEPA) requires the government to notify the public through hearings about projects that could have major environmental impacts.
7. How Does Carbon Dioxide That Is Injected Underground Stay There? Only certain geologic formations are amenable to carbon dioxide storage. In general, carbon dioxide can be stored in a layer of permeable rock that has a thick layer of impermeable rock above it. Permeable rock has pores through which fluids can flow and gather. Fluids cannot pass through impermeable rock, and so the top layer traps carbon dioxide that is injected into the permeable formation. Such cavities are the same type of formation that have trapped crude oil and natural gas over millions of years, and geologic formations are already used for disposal of hazardous wastes, so the idea of injecting a fluid underground for storage is not completely new.
1. How Are You Going to Decide Where to Do Field-Testing?
The decision to implement a carbon sequestration project will be based on several factors, including policy, commercial aspects, and local interests. Sites that are chosen will be those that rank the highest for these considerations. The program will provide ample opportunity for community involvement to ensure that a project is in the local interest. In particular, there is a Federal NEPA process that provides the opportunity for community input into the design and implementation of the project. Furthermore, the Carbon Sequestration Regional Partnerships will solicit input and feedback on the use of carbon sequestration in order to improve the design of sequestration projects in their regions.
2. Why Go to All this Trouble if Climate Change Isn’t Supposed to Happen for 100 Years?
As the old maxim goes, “An ounce of prevention is worth a pound of cure.” Efforts to test and develop carbon dioxide sequestration are part of a proactive strategy that will enable citizens, policy makers, industrial participants, and others to understand the benefits and challenges of carbon sequestration in order to decide whether to use it as a significant option for mitigating greenhouse gas emissions in the future. By beginning now, the program allows for the necessary research and development to see if carbon sequestration can be used to help meet the nation’s goal of reducing greenhouse gas intensity.
Many scientists believe that the Earth’s climate is already changing as a result of increasing greenhouse gas emissions from human activities. Thus far, this change has been gradual, and not always noticeable. Nevertheless, a sensible strategy is to begin reducing greenhouse gas intensity now, rather than waiting to act until after a potential dramatic climate shift happens in the future. Preventive action will limit future environmental damage, reduce the amount of money we will need to spend overall, and reduce the potential loss of human life that might accompany such a shift.
3. What Alternatives Are Being Considered in Addition to Carbon Dioxide Sequestration? Why Should We Spend Our Scarce Resources on this Program? Ideally, it would be best if we did not create excess carbon dioxide in the first place. But right now our principal energy systems are based on fossil fuels, and burning fossil fuels generates carbon dioxide emissions. That means when we drive a car, mow the grass, heat our homes, or use electricity (in most cases) we’re generating carbon dioxide. U.S. policies, like the Global Climate Change Initiative, are aimed at determining what we can do now to reduce carbon dioxide intensity through the use of renewable energy sources, energy conservation, and sequestration, while we develop improved energy systems that will emit less carbon dioxide than we do today.
Since 1990 renewable sources have accounted for about 7% of our energy. By 2020, we expect the use of renewables to grow but still account for about the same percentage of our overall energy picture. Renewables are a key part of the broad strategy to limit carbon dioxide emissions while maintaining a strong economy. We can’t change our energy systems overnight. But, we can make the workhorse technologies, the ones that we depend on now, more efficient and less polluting when it comes to carbon dioxide emissions, and we can continue to expand the use of renewables.
That said, our fossil fuel-based energy system has been in place for over a century and is supported by an immense investment in infrastructure. As a result, this mature network delivers energy at a reasonable price. Shifting to alternative sources of energy must be done gradually to maintain low prices for energy and to help maintain a strong economy. If we start to reduce our emissions from existing sources of energy and at the same time start to increase investment in alternative energy, we can do so without a big shock to the economy. In this way, carbon sequestration can help to serve as a bridge to new technologies such as hydrogen. The scale of the climate change problem is huge, meaning that we will need both sequestration and aggressive development of renewable technologies to make a difference.
Ideas on Cost – what this will cost us?
Adding carbon sequestration to the existing energy infrastructure will be an added cost – a significant one. Estimates of exact costs are poor at best for a variety of reasons including the fact that we are not talking about widespread use at the moment – many estimates look at a climate policy that results in many of these being built and operated. Second, they have not been built at commercial scale, so we don’t know the final price. And third, if compared to other options for reducing CO2 then this option is more cost-competitive.
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