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Title: Effective detection of CO2 leakage: a comparison of groundwater sampling and pressure monitoring

Abstract

Shallow aquifer monitoring is likely to be a required aspect to any geologic CO2 sequestration operation. Collecting groundwater samples and analyzing for geochemical parameters such as pH, alkalinity, total dissolved carbon, and trace metals has been suggested by a number of authors as a possible strategy to detect CO2 leakage. The effectiveness of this approach, however, will depend on the hydrodynamics of the leak-induced CO2 plume and the spatial distribution of the monitoring wells relative to the origin of the leak. To our knowledge, the expected effectiveness of groundwater sampling to detect CO2 leakage has not yet been quantitatively assessed. In this study we query hundreds of simulations developed for the National Risk Assessment Project (US DOE) to estimate risks to drinking water resources associated with CO2 leaks. The ensemble of simulations represent transient, 3-D multi-phase reactive transport of CO2 and brine leaked from a sequestration reservoir, via a leaky wellbore, into an unconfined aquifer. Key characteristics of the aquifer, including thickness, mean permeability, background hydraulic gradient, and geostatistical measures of aquifer heterogeneity, were all considered uncertain parameters. Complex temporally-varying CO2 and brine leak rate scenarios were simulated using a heuristic scheme with ten uncertain parameters. The simulations collectively predictmore » the spatial and temporal evolution of CO2 and brine plumes over 200 years in a shallow aquifer under a wide range of leakage scenarios and aquifer characteristics. Using spatial data from an existing network of shallow drinking water wells in the Edwards Aquifer, TX, as one illustrative example, we calculated the likelihood of leakage detection by groundwater sampling. In this monitoring example, there are 128 wells available for sampling, with a density of about 2.6 wells per square kilometer. If the location of the leak is unknown a priori, a reasonable assumption in many cases, we found that the leak would be detected in at least one of the monitoring wells in less than 10% of the scenarios considered. This is because plume sizes are relatively small, and so the probability of detection decreases rapidly with distance from the leakage point. For example, 400m away from the leakage point there is less than 20% chance of detection. We then compared the effectiveness of groundwater quality sampling to shallow aquifer and/or reservoir pressure monitoring. For the Edwards Aquifer example, pressure monitoring in the same monitoring well network was found to be even less effective that groundwater quality monitoring. This is presumably due to the unconfined conditions and relatively high permeability, so pressure perturbations quickly dissipate. Although specific results may differ from site to site, this type of analysis should be useful to site operators and regulators when selecting leak detection strategies. Given the spatial characteristics of a proposed monitoring well network, probabilities of leakage detection can be rapidly calculated using this methodology. Although conditions such as these may not be favorable for leakage detection in shallow aquifers, leakage detection could be much more successful in the injection reservoir. We demonstrate proof-of-concept for this hypothesis, presenting a simulation where there is measurable pressure change at the injection well due to overpressurization, fault rupture, and consequent leakage up the fault into intermediate and shallow aquifers. The size of the detectible pressure change footprint is much larger in the reservoir than in either of the overlying aquifers. Further exploration of the range of conditions for which this technique would be successful is the topic of current study.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE)
OSTI Identifier:
1360693
Report Number(s):
LA-UR-14-27155
Journal ID: ISSN 1876-6102
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
Energy Procedia (Online)
Additional Journal Information:
Journal Name: Energy Procedia (Online); Journal Volume: 63; Journal ID: ISSN 1876-6102
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Keating, Elizabeth, Dai, Zhenxue, Dempsey, David, and Pawar, Rajesh. Effective detection of CO2 leakage: a comparison of groundwater sampling and pressure monitoring. United States: N. p., 2014. Web. https://doi.org/10.1016/j.egypro.2014.11.448.
Keating, Elizabeth, Dai, Zhenxue, Dempsey, David, & Pawar, Rajesh. Effective detection of CO2 leakage: a comparison of groundwater sampling and pressure monitoring. United States. https://doi.org/10.1016/j.egypro.2014.11.448
Keating, Elizabeth, Dai, Zhenxue, Dempsey, David, and Pawar, Rajesh. Wed . "Effective detection of CO2 leakage: a comparison of groundwater sampling and pressure monitoring". United States. https://doi.org/10.1016/j.egypro.2014.11.448. https://www.osti.gov/servlets/purl/1360693.
@article{osti_1360693,
title = {Effective detection of CO2 leakage: a comparison of groundwater sampling and pressure monitoring},
author = {Keating, Elizabeth and Dai, Zhenxue and Dempsey, David and Pawar, Rajesh},
abstractNote = {Shallow aquifer monitoring is likely to be a required aspect to any geologic CO2 sequestration operation. Collecting groundwater samples and analyzing for geochemical parameters such as pH, alkalinity, total dissolved carbon, and trace metals has been suggested by a number of authors as a possible strategy to detect CO2 leakage. The effectiveness of this approach, however, will depend on the hydrodynamics of the leak-induced CO2 plume and the spatial distribution of the monitoring wells relative to the origin of the leak. To our knowledge, the expected effectiveness of groundwater sampling to detect CO2 leakage has not yet been quantitatively assessed. In this study we query hundreds of simulations developed for the National Risk Assessment Project (US DOE) to estimate risks to drinking water resources associated with CO2 leaks. The ensemble of simulations represent transient, 3-D multi-phase reactive transport of CO2 and brine leaked from a sequestration reservoir, via a leaky wellbore, into an unconfined aquifer. Key characteristics of the aquifer, including thickness, mean permeability, background hydraulic gradient, and geostatistical measures of aquifer heterogeneity, were all considered uncertain parameters. Complex temporally-varying CO2 and brine leak rate scenarios were simulated using a heuristic scheme with ten uncertain parameters. The simulations collectively predict the spatial and temporal evolution of CO2 and brine plumes over 200 years in a shallow aquifer under a wide range of leakage scenarios and aquifer characteristics. Using spatial data from an existing network of shallow drinking water wells in the Edwards Aquifer, TX, as one illustrative example, we calculated the likelihood of leakage detection by groundwater sampling. In this monitoring example, there are 128 wells available for sampling, with a density of about 2.6 wells per square kilometer. If the location of the leak is unknown a priori, a reasonable assumption in many cases, we found that the leak would be detected in at least one of the monitoring wells in less than 10% of the scenarios considered. This is because plume sizes are relatively small, and so the probability of detection decreases rapidly with distance from the leakage point. For example, 400m away from the leakage point there is less than 20% chance of detection. We then compared the effectiveness of groundwater quality sampling to shallow aquifer and/or reservoir pressure monitoring. For the Edwards Aquifer example, pressure monitoring in the same monitoring well network was found to be even less effective that groundwater quality monitoring. This is presumably due to the unconfined conditions and relatively high permeability, so pressure perturbations quickly dissipate. Although specific results may differ from site to site, this type of analysis should be useful to site operators and regulators when selecting leak detection strategies. Given the spatial characteristics of a proposed monitoring well network, probabilities of leakage detection can be rapidly calculated using this methodology. Although conditions such as these may not be favorable for leakage detection in shallow aquifers, leakage detection could be much more successful in the injection reservoir. We demonstrate proof-of-concept for this hypothesis, presenting a simulation where there is measurable pressure change at the injection well due to overpressurization, fault rupture, and consequent leakage up the fault into intermediate and shallow aquifers. The size of the detectible pressure change footprint is much larger in the reservoir than in either of the overlying aquifers. Further exploration of the range of conditions for which this technique would be successful is the topic of current study.},
doi = {10.1016/j.egypro.2014.11.448},
journal = {Energy Procedia (Online)},
number = ,
volume = 63,
place = {United States},
year = {2014},
month = {12}
}

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Works referenced in this record:

Brine Displacement and Leakage Detection Using Pressure Measurements in Aquifers Overlying CO2 Storage Reservoirs
journal, February 2009


Leakage characterization through above-zone pressure monitoring: 1—Inversion approach
journal, November 2012


Leakage characterization through above-zone pressure monitoring: 2—Design considerations with application to CO2 storage in saline aquifers
journal, November 2012


Detecting leakage of brine or CO2 through abandoned wells in a geological sequestration operation using pressure monitoring wells
journal, January 2011


Inducing a CO2 Leak into a Shallow Aquifer (CO2FieldLab Eurogia+ Project): Monitoring the CO2 Plume in Groundwaters
journal, January 2013


Key factors for determining groundwater impacts due to leakage from geologic carbon sequestration reservoirs
journal, October 2014

  • Carroll, Susan A.; Keating, Elizabeth; Mansoor, Kayyum
  • International Journal of Greenhouse Gas Control, Vol. 29
  • DOI: 10.1016/j.ijggc.2014.07.007

Transmissivity estimation for highly heterogeneous aquifers: comparison of three methods applied to the Edwards Aquifer, Texas, USA
journal, July 2006


Early detection of brine and CO2 leakage through abandoned wells using pressure and surface-deformation monitoring data: Concept and demonstration
journal, December 2013


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