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Permanence and Safety of CCS

HOW DO WE KNOW THAT CO2 STORAGE IS SAFE?

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

Oil, natural gas, and naturally occurring carbon dioxide (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.

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 U.S. Department of Energy (DOE) in various geologic settings across the United States. These include injection efforts underway by the Regional Carbon Sequestration Partnerships (RCSPs). To date, more than 14 million metric tons (MMT) of CO2 have been successfully injected and 10.5 MMT of CO2 has been successfully stored as part of the RCSP large-scale storage efforts. The vast amount of evidence attained from EOR, gas storage, research and development (R&D), and commercial-scale carbon capture and storage (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 complex 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 National Energy Technology Laboratory (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 CO2storage 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.
NRAP is building toolsets and improving the science base to address key questions about potential impacts related to release of CO2or brine from the storage reservoir, and potential ground-motion impacts due to injection of CO2.

Myth: Carbon dioxide 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.


HOW IS A CO2 STORAGE SITE MONITORED?

Setting up soil gas monitoring locations in proximity to a CO2 storage site
Setting up soil gas monitoring locations in proximity to a CO2 storage site

Monitoring, verification, accounting (MVA), and assessment is an important part of making storage of carbon dioxide (CO2) safe, effective, and permanent in all types of geologic formations. Monitoring occurs before, during, and after the injection phase of a CO2 storage project. The MVA plan for storage projects can have broad scopes, covering CO2 storage conformance and containment, monitoring techniques for internal quality control, and verification and accounting for regulators and monetizing benefits of geologic storage. The location of the injected CO2 plume in underground formations can also be determined, via monitoring, to satisfy operating regulatory requirements to ensure that potable groundwater and ecosystems are protected throughout the project lifecycle.

WHERE DOES MONITORING AT A STORAGE SITE OCCUR?

Monitoring technologies can be deployed for atmospheric, near-surface, and subsurface applications to ensure that injected CO2 remains in the targeted storage formation, as well as to check for indicators of possible CO2 migration out of a storage complex

WHAT ARE THE TYPES OF MONITORING TOOLS AND TECHNIQUES?

There is a large portfolio of technologies available for monitoring of storage projects, many of which are highly developed due to decades of use and experience gained in the oil and gas industry, as well as through advancements through targeted research and development (R&D). 

Researcher sampling surface water at a DOE-supported CO2 storage site
Researcher sampling surface water at a DOE-supported CO2 storage site
  • Atmospheric monitoring tools are used to measure CO2 density and flux in the atmosphere above underground storage sites. Three types of tools that are used for identifying and quantifying CO2 in the atmosphere are optical CO2 sensors, atmospheric CO2 tracers, and eddy covariance (EC) flux measurement techniques.
  • Near-surface monitoring techniques are used to measure CO2 in regions that extend from the top of the soil zone down to the shallow groundwater zone. Tools that measure CO2 effects in the near-surface region include geochemical monitoring tools, surface displacement monitoring tools, and ecosystem stress monitoring tools.
  • Subsurface monitoring tools are used to detect and monitor the migration of CO2 that has been injected into a geologic storage reservoir, characterize faults, fractures, and monitor for any potential micro-seismic activity that may be present in the storage complex.
    • Subsurface monitoring tools include well logging tools, downhole monitoring tools, subsurface fluid sampling and tracer analysis, seismic-imaging methods, high-precision gravity methods, and electrical techniques.

Through the National Energy Technology Laboratory's (NETL) Advanced Storage R&D area, research has allowed for a portfolio of available monitoring technologies for all types of CO2 storage situations. NETL continues to develop and field test advanced monitoring technologies, as well as supporting protocols, to decrease the cost and uncertainty in measurements needed to satisfy regulations for tracking the fate of subsurface CO2 and quantify any emissions to the atmosphere.

Various sampling methods being used at the Citronelle CO2 Storage Project (SECARB). Methods include: A. gas-lift; B. electric submersible pump; C. Kuster sampler; and D. U-tube sampler.
Various sampling methods being used at the Citronelle CO2 Storage Project (SECARB). Methods include: A. gas-lift; B. electric submersible pump; C. Kuster sampler; and D. U-tube sampler.

Myth: It is impossible to adequately monitor CO2 injection sites.

Reality: Extensive monitoring of CO2 injection sites is already taking place both at the surface and in the subsurface. This is an important regulatory requirement for these projects to operate in the United States.


WHAT REGULATIONS ARE IN PLACE TO GOVERN CO2 INJECTION(S)?

Artistic rendering of an EPA UIC Class VI injection well designed for safely injecting CO2 underground for long-term storage.

The U.S. Environmental Protection Agency (EPA) is tasked with the responsibility of establishing and enforcing any regulations associated with injecting and storing carbon dioxide (CO2) in the subsurface. In December 2010, EPA finalized minimum Federal requirements under the Safe Drinking Water Act (SDWA) for underground CO2 injection for the purpose of geologic storage. This final rule applies to owners or operators of wells that will be used to inject CO2 into the subsurface for the purpose of long-term storage. It establishes a new class of well, Class VI, as part of the Underground Injection Control (UIC) Program. 

The UIC Class VI regulations set minimum technical criteria for the permitting, geologic site characterization, corrective action (if necessary), financial responsibility, well construction, operation, monitoring, well plugging, post-injection site care (PISC), and site closure of Class VI wells for the purposes of protecting underground sources of drinking water (USDWs).

The elements of this rulemaking are based on the existing UIC regulatory framework, with modifications to address the unique nature of CO2 injection for geologic storage. This rule will help to ensure consistency in permitting underground CO2 injection at geologic storage operations across the United States and provide requirements to prevent endangerment of USDWs. In addition to these Federal requirements, many states have either enacted carbon capture and storage (CCS) requirements or are in the process of doing so.

The U.S. Department of Energy (DOE) has no responsibility in developing regulations for underground CO2 storage. However, DOE does support the continued development and field testing of technologies that can be used by operators to verify that the regulations relating to the safe storage of CO2underground are met.

Myth: Current regulations are inadequate to address the underground CO2 injection.

Reality: There are both Federal and state regulations that govern underground CO2 injection.

 


HOW IS THE FEDERAL GOVERNMENT SUPPORTING THE DEPLOYMENT OF CCS TECHNOLOGIES?

A total of five Best Practices Manuals were revised in 2017.
A total of five Best Practices Manuals were revised in 2017.

The U.S. Department of Energy (DOE) launched its Carbon Capture and Storage (CCS) Program in 1997. Consistent with Administration and Congressional priorities, CCS continues to be a key element of DOE’s research and development (R&D) portfolio.

The Carbon Storage Program is implemented by the National Energy Technology Laboratory (NETL) within DOE’s Office of Fossil Energy (FE). The mission of the Carbon Storage Program is to develop technologies, for commercial readiness beginning in 2025, that ensure safe, secure, efficient, and affordable carbon dioxide (CO2) injection and containment in storage complex in diverse geologic settings

Lessons learned from developing and field testing these technologies are documented in a series of Best Practice Manuals (BPMs).

Myth: Little is being done by the Federal government to advance CCS technologies.

Reality: DOE has had an extensive CCS research program underway for more than two decades. There is considerable cost-share from private entities as well.