Natural and introduced tracers in the atmosphere can be used for monitoring of a possible CO2 release from geologic storage reservoirs. Natural tracers are chemical compounds that are associated with CO2 in the subsurface, near-surface, or atmosphere. These include CH4, radon, noble gases, and isotopes of CO2. Introduced tracers, such as sulfur hexafluoride (SF6) and perfluorocarbon tracer (PFT), are chemical compounds that may be injected into a geologic reservoir along with the CO2 in order to give the injected CO2 a unique fingerprint that can be recognized in aboveground emissions. Tracer monitoring can take place in the near-surface and subsurface regions as well.1National Energy Technology Laboratory. (2017). Best practices: Monitoring, verification, and accounting (MVA) for geologic storage projects. National Energy Technology Laboratory, U.S. Department of Energy. https://netl.doe.gov/sites/default/files/2018-10/BPM-MVA-2012.pdf
Isotopic and Chemical Tracers Tool Summary
- Description: Natural and injected chemical compounds that are monitored in air to help detect CO2 released to the atmosphere.
- Benefits: Used as a proxy for CO2, when direct observation of a CO2 release is not adequate. Also used to track potential CO2 plumes.
- Challenges: In some cases, analytical equipment is not available onsite, and samples need to be analyzed offsite. Background/baseline levels must be established. Tracers may not behave the same as CO2 along the migration pathway.2National Energy Technology Laboratory. (2017). Best practices: Monitoring, verification, and accounting (MVA) for geologic storage projects. National Energy Technology Laboratory, U.S. Department of Energy. https://netl.doe.gov/sites/default/files/2018-10/BPM-MVA-2012.pdf
A research team injects a fluorinated tracer into the subsurface at a test site in Tennessee. Monitoring will then involve collecting data to look for evidence of the tracer.
Atmospheric perfluorocarbon tracer (perfluoroethylcyclohexane) sampling was part of a shallow, controlled underground CO2 leak experiment held at Montana State University in Bozeman, Montana in 2008. Tracer dispersion was measured using a tethered balloon system with multi-tube remote samplers at elevations of 10 m, 20 m, and 40 m above ground level, as well as a ground-based portable tower with monitors containing sorbent material to collect the tracer at 1 m, 2 m, 3 m, and 4 m above ground level. As anticipated with a controlled release, tracer was consistently detected at elevated concentrations downwind of the release point. This field study demonstrated the feasibility of remote sampling with unmanned aerial systems at future carbon storage sites.3Pekney, N., Wells, A., Diehl, J., McNeil, M., Lesko, N., Armstrong, J., & Ference, R. (2012) Atmospheric monitoring of a perfluorocarbon tracer at the 2009 ZERT Center Experiment. Atmospheric Environment. 47, 124-132.
Sampling balloon towed to deployment in the field (left) at the field experiment station in Montana. At right, the balloon is shown in flight with the multi-tube remote samplers (MTRS) in tow.4National Energy Technology Laboratory. (2017). Best practices: Monitoring, verification, and accounting (MVA) for geologic storage projects. National Energy Technology Laboratory, U.S. Department of Energy. https://netl.doe.gov/sites/default/files/2018-10/BPM-MVA-2012.pdf
Image Credits: Photo Courtesy of the National Energy Technology Laboratory