Permanence and Safety of CCS


Oil, natural gas and naturally occurring CO2 gas deposits have been naturally trapped and stored within subsurface geologic formations for millions of years, providing evidence that it is possible to store CO2 in similar geologic formations for very long periods of time. These deposits provide information about the geologic conditions needed for secure CO2 storage.

A CO2 injection well in operation as part of an enhanced oil recovery (EOR) operation at a mature oil field in the United States.

In addition, the United States has been safely injecting natural gas into underground formations that are able to store gas until it is needed. This geological and engineering experience is being applied to storage of CO2, a safer, non-combustible gas. Additional evidence that CO2 can be safely stored underground comes from a more than 40 year old process called enhanced oil recovery (EOR) where CO2 has been injected underground to increase oil production.

Finally, there have been large-scale commercial and research-related trial CO2 storage operations in the United States and around the world that have demonstrated effective CO2 storage. Examples of efforts that have been successfully storing CO2 on a large-scale include the Sleipner Project in the North Sea (in operation since 1996) and the Weyburn Project in Saskatchewan (operated from 2000 to 2012). In addition, large-scale CO2 storage research projects are being conducted by the DOE in various geologic settings across the United States. These include injection efforts underway by the Regional Carbon Sequestration Partnerships (RCSP). To date, nearly 8 million metric tons of CO2 have been successfully injected and stored as part of the RCSP large-scale storage efforts. The vast amount of evidence attained from EOR, gas storage, research and development, and commercial-scale CCS efforts suggests that CO2 storage is safe, assuming that sites are well selected, designed, and operated appropriately.

Ensuring safe injection and storage of CO2 requires that the risks associated with these large-scale field projects need to be identified and quantified. Storage risks are related to CO2 migrating out of its storage target area and the physical and chemical effects that the injected CO2 may have on the subsurface. DOE research is developing technologies and procedures to identify, reduce, and/or mitigate these risks to ensure safe operations. The NETL has undertaken efforts to identify and quantify risks through a multi-lab initiative called the National Risk Assessment Partnership (NRAP). The goal of NRAP is to develop a science-based methodology for calculating risks at any CO2 storage site while providing necessary scientific and technological advances to support that methodology. The NRAP toolsets will include methodologies and models that predict behavior of each component of the subsurface systems.

NRAP is building toolsets and improving the science base to address key questions about potential impacts related to release of CO2 or brine from the storage reservoir, and potential ground-motion impacts due to injection of CO2

Myth: CO2 injection is unlikely to be safe because it is expected to migrate to the surface.
Reality: Considerable experience with the injection of CO2 for EOR, underground storage of natural gas, and continuous monitoring at several large-scale CCS injection projects around the world indicates that CO2 injection is expected to be safe.

What are the ways that CO2 storage sites are monitored to make sure that the CO2 remains in place?