Title: Measurements of ²²²Rn, ²²⁰Rn, and CO₂ Emissions in Natural CO₂ Fields in Wyoming: MVA Techniques for Determining Gas Transport and Caprock Integrity

Abstract

An integrated field-laboratory program evaluated the use of radon and CO₂ flux measurements to constrain source and timescale of CO₂ fluxes in environments proximate to CO₂ storage reservoirs. By understanding the type and depth of the gas source, the integrity of a CO₂ storage reservoir can be assessed and monitored. The concept is based on correlations of radon and CO₂ fluxes observed in volcanic systems. This fundamental research is designed to advance the science of Monitoring, Verification, and Accounting (MVA) and to address the Carbon Storage Program goal of developing and validating technologies to ensure 99 percent storage performance. Graduate and undergraduate students conducted the research under the guidance of the Principal Investigators; in doing so they were provided with training opportunities in skills required for implementing and deploying CCS technologies. Although a final method or “tool” was not developed, significant progress was made. The field program identified issues with measuring radon in environments rich in CO₂. Laboratory experiments determined a correction factor to apply to radon measurements made in CO₂-bearing environments. The field program also identified issues with radon and CO₂-flux measurements in soil gases at a natural CO₂ analog. A systematic survey of radon and CO₂ flux inmore » soil gases at the LaBarge CO₂ Field in Southwest Wyoming indicates that measurements of ²²²Rn (radon), ²²⁰Rn (thoron), and CO₂ flux may not be a robust method for monitoring the integrity of a CO₂ storage reservoir. The field program was also not able to correlate radon and CO₂ flux in the CO₂-charged springs of the Thermopolis hydrothermal system. However, this part of the program helped to motivate the aforementioned laboratory experiments that determined correction factors for measuring radon in CO₂-rich environments. A graduate student earned a Master of Science degree for this part of the field program; she is currently employed with a geologic consulting company. Measurement of radon in springs has improved significantly since the field program first began; however, in situ measurement of ²²²Rn and particularly ²²⁰Rn in springs is problematic. Future refinements include simultaneous salinity measurements and systematic corrections, or adjustments to the partition coefficient as needed for more accurate radon concentration determination. A graduate student earned a Master of Science degree for this part of the field program; he is currently employed with a geologic consulting company. Both graduate students are poised to begin work in a CCS technology area. Laboratory experiments evaluated important process-level fundamentals that effect measurements of radon and CO₂. Laboratory tests established that fine-grained source minerals yield higher radon emissivity compared to coarser-sized source minerals; subtleties in the dataset suggest that grain size alone is not fully representative of all the processes controlling the ability of radon to escape its mineral host. Emissivity for both ²²²Rn and 220Rn increases linearly with temperature due to reaction of rocks with water, consistent with faster diffusion and enhanced mineral dissolution at higher temperatures. The presence of CO₂ changes the relative importance of the factors that control release of radon. Emissivity for both ²²²Rn and ²²⁰Rn in CO₂-bearing experiments is greater at all temperatures compared to the experiments without CO₂, but emissivity does not increase as a simple function of temperature. Governing processes may include a balance between enhanced dissolution versus carbonate mineral formation in CO₂-rich waters.« less

Authors:

Kaszuba, John ^[1]; Sims, Kenneth ^[1]

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+ Show Author Affiliations

1. Univ. of Wyoming, Laramie, WY (United States)

Publication Date:

Tue Sep 30 00:00:00 EDT 2014

Research Org.:

Univ. of Wyoming, Laramie, WY (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1174142

DOE Contract Number:  

FE0002112

Resource Type:

Technical Report

Country of Publication:

United States

Language:

English

Subject:

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 54 ENVIRONMENTAL SCIENCES