Process-Based Environmental Monitoring at CO2 Storage Sites

Real-time attribution of CO₂ found in soils, whether from natural or induced environmental changes

Principal Investigator: Katherine Romanak

Keynote

Historically, monitoring for carbon dioxide (CO₂) at the ground surface above carbon storage sites required years of baseline data. With the urgent need to abate emissions, many projects do not have the time required to gather this data or it is simply unavailable. To bypass this dilemma and improve accuracy, a method to detect CO₂ and its origin in real time was developed.

By measuring multiple gas concentrations within the subsurface soil, the relative changes between CO₂ and other gases can give a clue to the origin of the CO₂.

This newly developed approach examines chemical relationships between vadose zone—the ground above natural drinking water— N₂, O₂, CO₂, and CH₄ to promptly distinguish between a leakage signal and CO₂ fluctuations due to natural processes like biological respiration.

As stated in the pioneering paper, the method uses sequential inspection of the following gas concentration ratios and their signal:

O₂ versus CO₂ to distinguish in‐situ vadose zone background processes (biologic respiration, methane oxidation, and CO₂ dissolution) from exogenous deep leakage input,
CO₂ versus N₂ to further distinguish dissolution of CO₂ from exogenous deep leakage input, and
CO₂ versus N₂/O₂ to assess the degree of respiration, CH₄ oxidation and atmospheric mixing/dilution occurring in the system.

These gases vary predictably with natural and induced environmental changes—the changes indicative of whether or not a leak is detected. This relatively simple tool for incident response by fingerprinting anomalies is cost-effective, accurate, and can be used in areas lacking background data. As part of the IPAC-CO₂ Kerr investigation (2010–2011), this method was used to successfully attribute a CO₂ anomaly garnering leak allegations, ruling out CO₂ contamination. Download a presentation detailing the investigation here.

The traditional challenges facing this environmental monitoring and the benefits of the new technique are described below.

Challenges of concentration-based monitoring

1–3 years cannot capture the full variation in natural CO₂.
Background measurements time, cost, and labor intensive.
Leakage signals smaller than natural variability may be overlooked
Background concentrations cannot be measured everywhere within the area of review.
An incident can occur in an area with no background monitoring.

Benefits of process-based soil gas method

Does not rely on background CO₂ measurements
Uses ratios among major gases (CO₂, CH₄, N₂, O₂)
Discerns process
- In-situ from exogenous gas
- Mixing with air
- CO₂ dissolution
- Oxidation of CH₄ into CO₂ (important for CO₂-EOR site monitoring)
Being developed for groundwater and marine environments

Publications

Anderson, J.S., Romanak, K.D., Yang, C., Lu, J., Hovorka, S.D., and Young, M.H. 2017. Gas source attribution techniques for assessing leakage at geologic CO₂ storage sites: Evaluating a CO₂ and CH₄ soil gas anomaly at the Cranfield CO₂-EOR site. Chemical Geology, 454 (93-104). https://doi.org/10.1016/j.chemgeo.2017.02.024.

Romanak, K.D., and Bomse, D.S. 2020. Field assessment of sensor technology for environmental monitoring using a process-based soil gas method at geologic CO₂ storage sites. International Journal of Greenhouse Gas Control, 96. https://doi.org/10.1016/j.ijggc.2020.103003.

Romanak, K.D., Bennett, P.C., Yang, C., and Hovorka, S.D. 2012. Process‐based approach to CO₂ leakage detection by vadose zone gas monitoring at geologic CO2 storage sites. Geophysical Research Letters, 39 (15). https://doi.org/10.1029/2012GL052426.

Romanak, K.D., Sherk, G.W., Hovorka, S.D., Yang, C. 2013. Assessment of Alleged CO₂ Leakage at the Kerr Farm using a Simple Process-based Soil Gas Technique: Implications for Carbon Capture, Utilization, and Storage (CCUS) Monitoring. Energy Procedia, 37 (4242-4248). https://doi.org/10.1016/j.egypro.2013.06.326.

Romanak, K.D., Womack, G.L., Bomse, D.S. 2014. Field Test of in Situ Sensor Technology for Process-based Soil Gas Monitoring. Energy Procedia, 63 (4027-4030). https://doi.org/10.1016/j.egypro.2014.11.433.

Romanak, K.D., Yang, C., and Darvari, R. 2017. Towards a Method for Leakage Quantification and Remediation Monitoring in the Near-surface at Terrestrial CO₂ Geologic Storage Sites. Energy Procedia, 114 (3855-3862). https://doi.org/10.1016/j.egypro.2017.03.1517.

Sherk, G.W., Romanak, K.D., Dale, J., Gilfillan, S.M.V., Haszeldine, R.S., Ringler, E.S., Wolaver, B.D. and Yang, C. 2011. The Kerr investigation: Findings of the investigation into the impact of CO₂ on the Kerr property, final report. IPAC-CO2 Inc., Regina, Saskatchewan, Canada.

Yang, C., Romanak, K., Hovorka, S. D., Holt, R. M., Lindner, J., & Trevino, R. 2013. Near-Surface Monitoring of Large-Volume CO₂ Injection at Cranfield: Early Field Test of SECARB Phase III. Society of Petroleum Engineers. https://doi.org/10.2118/163075-PA.

Yang, C., Romanak, K.D., Reedy, R.C. et al. 2017. Soil gas dynamics monitoring at a CO₂-EOR site for leakage detection. Geomech. Geophys. Geo-energ. Geo-resour. 3, 351–364. https://doi.org/10.1007/s40948-017-0053-7.

Patents

Process-based approach for the detection of CO₂ injectate leakage
https://patents.google.com/patent/US9816972B2/en

Process-based approach for the detection of deep gas invading the surface
https://patents.google.com/patent/US9645129B2/en

Gas sensor to enhance implementation of a process-based leakage monitoring method
https://patents.google.com/patent/US20160202186A1/en

This work was funded by the U.S. Department of Energy through the Office of the Governor of Texas (contract DE‐FG04‐9OAL65847) and the National Energy Technology Laboratory (contract DE FG26‐05NT42590) through the Southeast Regional Carbon Sequestration Partnership.

Last Updated: July 16, 2020