NETL is partnering with the University of Wyoming (UW) to conduct a systematic survey of discrete radon (Rn) and CO2 flux measurements in soil gases at field sites in Wyoming where previous work has demonstrated geologic correspondence of moderate to high gamma background radiation (i.e., potential Rn degassing) with naturally-occurring CO2 (Figure 1). Natural CO2 analogues provide a means of understanding and predicting behavior in geologic storage reservoirs, particularly as test beds for investigating and improving technologies and protocols aimed at assessing the integrity of caprock formations. Radon is a noble gas and the only naturally occurring radioactive gas. It has two isotopes, 222Rn and 220Rn, both of which are relevant to this project. 222Rn is a short-lived decay product derived from the 238U (Uranium) decay series, with a half-life of 3.82 days. 220Rn is a decay product derived from the 232Th (Thorium) decay series and has an even shorter half-life 56 seconds) that makes it useful in identifying areas of very fast soil-gas transport. Elevated Rn emissions are strongly correlated with high CO2 emissions in volcanic systems; thus, 222Rn provides a means to identify deep CO2 flow in geologic storage projects, and map active, high porosity regions prone to CO2 movement. This proposed Rn-CO2 relationship will be tested to determine if discrete radon and CO2 fluxes could be used to indicate potential leakage in CCS projects.
Since chemical reactions affect the distribution of nuclides within the 238U and 232Th decay series (i.e., U-series), UW will replicate field conditions in a laboratory setting in order to evaluate the effects of mixed phase CO2-H2O-rock reactions on subsequent Rn degassing. Measuring CO2 and both isotopes of Rn from the same samples will constrain the relationship between Rn degassing and CO2 flux. The different half-lives provide important constraints on the source/depth of the Rn since 220Rn—because of its extremely short half-life (56 seconds)—will decay over long transport times. Because of its short half-life, 222Rn possesses the unique advantage of being used to estimate the timescale of CO2 migration. However, because the main source of the measured Rn (shallow soil degassing, deep reservoir degassing, or both) is undetermined, the nature and relevance of the temporal constraints from 222Rn remain uncertain.
Increased attention is being placed on research into technologies that capture and store carbon dioxide (CO2). Carbon capture and storage (CCS) technologies offer great potential for reducing CO2 emissions and, in turn, mitigating global climate change without adversely influencing energy use or hindering economic growth.
Deploying these technologies in commercial-scale applications requires a significantly expanded workforce trained in various CCS specialties that are currently under-represented in the United States. Education and training activities are needed to develop a future generation of geologists, scientists, and engineers who possess the skills required for implementing and deploying CCS technologies.
The U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (NETL) has selected 43 projects to receive more than $12.7 million in funding, the majority of which is provided by the American Recovery and Reinvestment Act (ARRA) of 2009, to conduct geologic sequestration training and support fundamental research projects for graduate and undergraduate students throughout the United States. These projects will include such critical topics as simulation and risk assessment; monitoring, verification, and accounting (MVA); geological related analytical tools; methods to interpret geophysical models; well completion and integrity for long-term CO2 storage; and CO2 capture.
Overall the project will make a vital contribution to the scientific, technical, and institutional knowledge base necessary to establish frameworks for the development of commercial-scale CCS. By applying the geologic principles of field measurements at natural CO2 analogues in Wyoming with the geochemical principles of 222Rn, 220Rn, and CO2 measurements in laboratory and field settings, UW can evaluate and calibrate the use of naturally occurring Rn isotopes for evaluating the reliability of caprock formations. Instru-ments and techniques to analyze Rn and CO2 have already been developed for other industrial applications and can easily be deployed for sequestration leak detection and caprock integrity assessment. This work will increase the geologic sequestration knowledge base and continue to move CCS research towards more applied technologies.
The goal of the project is to determine whether quantitative measurement tech-niques for Rn activity and CO2 flux that have already been established for natural volcanic systems, can be applied to natural and laboratory CO2 analogues as a means of assessing caprock (seal) integrity and potential CO2 leakage for geologic storage projects. This project will provide training opportunities for two graduate students and one undergraduate student in geologic and geochemical skills required for implementing and deploying CCS technologies.
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