Authors / CoAuthors
Schroder, I.F. | Padarn, W. | Feitz, A.J.
Abstract
Geoscience Australia and the CO2CRC operate a controlled release facility in Canberra, Australia, designed for simulating subsurface emissions of CO2 by injecting gas into a horizontal well. Three controlled release experiments were conducted at this site during 2012-2013, over 7-9 week periods, to assess and develop near-surface monitoring technologies for application to carbon dioxide geological storage sites (Feitz et al., 2014). A key well-established technique for characterizing surface CO2 emission sources from controlled release sites or natural CO2 seeps is soil flux surveys. The technique is often considered as the benchmark technique for characterizing a site's emissions or as a baseline for comparing other measurement techniques, but has received less attention with regards to its absolute performance. The extensive soil gas surveys undertaken during Release 1 (Feb-May 2012) and Release 3 (Oct-Dec 2013) are the subject of this paper. Several studies have highlighted factors which can have an effect on soil flux measurements, including meteorological influences such as air pressure and wind speed, which can increase or suppress soil fluxes (Rinaldi et al. 2012). Work at the Canberra controlled release site has highlighted the influence groundwater has on the spatial distribution of fluxes.). In addition, there are several different methods available for inverting soil flux measurements to obtain the emission rate of a surveyed area. These range in complexity from planar averaging to geostatistical methods such as sequential Gaussian simulation (Lewicki et al. 2005). Each inversion technique relies on its own subset of assumptions or limitations, which can also impact the end emissions estimate. Thus deriving a realistic estimate of the total emission rate will depend on both environmental forcing as well as the applied inversion method. An in-house method for soil flux interpolation has been developed and is presented. A cubic interpolated surface is generated from all the measurement points (Figure 1), from which a background linear interpolated surface is subtracted off, leaving the net leakage flux. The background surface is prepared by identifying all background points matching a certain criteria (for this release experiment distance from release well was used) and interpolating only over those points. In these experiments, soil flux surveys were collected on a predefined grid, using an irregular sampling pattern with higher density of samples nearer to the leak hotspots to provide higher spatial resolution in the regions where flux changes most rapidly (Figure 2). The same release rate of 144 kgCO2/day was used for both experiments. It was observed that the surface flux distribution shifts markedly between experiments, most likely a function of seasonal differences (2012 was wet; 2013 was dry) and resulting differences in groundwater depth, soil saturation and the extent of the vadose zone.. The depth to the groundwater measured at monitoring wells in proximity to the release well was 0.85-1.2 m during the 2012 (wet) release whereas it ranged from 1.9-2.3 m during the 2013 (dry) release experiment. The horizontal well is located 2.0 m below the ground surface. This paper explores the performance of soil flux surveys for providing an accurate estimate of the release rate, using a series of soil flux surveys collected across both release experiments. Emission estimates are generated by applying several common inversion methods, which are then compared to the known release rate of CO2. An evaluation as to the relative suitability of different inversion methods will be provided based on their performance. Deviations from the measured release rate are also explored with respect to survey design, meteorological and groundwater factors, which can lead and inform the future deployment of soil flux surveys in a monitoring and verification program.
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nonGeographicDataset
eCat Id
90000
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
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2601
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Keywords
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- External PublicationAbstract
- ( Theme )
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- soils
- ( Theme )
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- carbon capture and storage
- ( Theme )
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- carbon dioxide
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Meteorology
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- Published_Internal
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2016-01-01T00:00:00
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climatologyMeteorologyAtmosphere
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