Permanence and Safety of CCS

How is a CO2 storage site monitored?

Monitoring, verification, and accounting (MVA) is an important part of making storage of CO2 safe, effective, and permanent in all types of geologic formations. Monitoring occurs before, during, and after during 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. In the United States, since Federal and State greenhouse gas (GHG) regulations and emission trading programs have been developed, monitoring has gained importance as a means to ensure CO2 has been safely and permanently stored underground throughout the lifecycle of a CCS project. 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.


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

Monitoring zones typical to and MVA tools available for a geologic CO2 storage site (click to enlarge)


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

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.

  • 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 NETL’s Core 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.

sampling-surface-water-faq.jpg   secarb-faq
Researcher sampling surface water at a DOE-supported CO2 storage site   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.

How is the process of ensuring safe CO2 storage regulated?