Carbon Sequestration
Where will the carbon dioxide be stored?
One of the things that makes the FutureGen power plant truly unique is the ability to capture the carbon dioxide—a greenhouse gas when released into the atmosphere—before it ever leaves the plant. The carbon dioxide is compressed and pumped deep underground for permanent storage in a process known as carbon sequestration.
There are several types of rock formations that can be used to store carbon dioxide. These include:
- Rock formations containing saline water
- Depleted oil and gas fields
- Unmineable coal seams
- Other formations, like salt domes
Source: Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC). Click for a larger version.
What makes these formations ideal for carbon dioxide storage is their porosity, permeability, and depth, and the presence of an impermeable caprock. Porosity, similar to void space between gumballs in a machine, allows the carbon dioxide to be stored in the rocks. High permeability allows the carbon dioxide to move through the target formation, the way a paper towel wicks up water. It is also important that the target formation be at a depth of more than 800 meters, where temperature and pressure are sufficient to keep the carbon dioxide in a very dense, liquid-like state.
FutureGen specifically targets rock formations containing saline water. These formations are thousands of feet below the earth's surface—far deeper than drinking water aquifers, and often much deeper than oil and gas deposits. Of all the rock formations identified above, rock formations containing saline water are one of the most abundant types of geologic formations that can be used to store carbon dioxide. These formations were selected for the long term storage of carbon dioxide so that the lessons learned from FutureGen will be replicable at many other locations around the world.
Will this kind of storage be permanent?
Yes. The rock formations used to store carbon dioxide are overlain by a thick caprock that serves as a seal. This caprock has properties that are opposite of the storage formations themselves, including:
- Low porosity - There is very little void space to hold fluids.
- Low permeability - The rock won't allow fluids to penetrate.
Once the carbon dioxide has been injected, it is buoyant within the formation and tends to rise, but the caprock prevents it from migrating upward. The caprock holds the carbon dioxide in place the same way hydrocarbon "traps" can hold oil and gas in place for millions of years. Proper site selection and engineering will help to ensure that the carbon dioxide stays below ground where it won't contribute to atmospheric greenhouse gas concentrations.
When a final site is selected, the FutureGen Alliance will complete an even more thorough evaluation of the site before carbon dioxide is injected. This evaluation will include modeling and field studies that will provide detailed information on the geologic characteristics of the selected site, and that will ensure the injection system is designed optimally for permanent storage of carbon dioxide.
After the carbon dioxide is injected, the Alliance will continue to monitor it by conducting periodic surveys with a sophisticated measuring, monitoring, and verification protocol. This monitoring will allow the Alliance to look underground to see what's happening to the carbon dioxide, enabling scientists to make sure that it is behaving as expected, and to make any modifications necessary to ensure the permanency of the storage system.