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| Titel |
Experimental determination of trace element mobility in UK North Sea sandstones under conditions of geological CO2 storage |
| VerfasserIn |
Kit Carruthers, Mark Wilkinson, Ian B. Butler |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135625
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| Publikation (Nr.) |
 EGU/EGU2016-16513.pdf |
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| Zusammenfassung |
| Offshore UK geological formations have the capacity to store > 100 years’ worth of UK CO2
output from industry and power generation, if utilised for carbon capture and storage
(CCS) schemes. During CO2 storage or CO2-Enhanced Oil Recovery (CO2-EOR),
formation waters may be produced at the surface to be disposed of into the marine
environment.
Laboratory and field scale studies, with an emphasis on the effects on onshore shallow
potable groundwaters, have shown that CO2 dissolution in formation waters during injection
and storage acidifies the waters and promotes mobilisation from the reservoir sandstones of
major and trace elements into solution. Of relevance to the UK context, eight of these
elements are specifically identified as potentially hazardous to the marine environment: As,
Cd, Cr, Cu, Hg, Ni, Pb, Zn.
Batch experiments using simple borosilicate flasks sat on heating mantles were used in
this study to determine concentrations of these 8 elements which could be leached from
selected North Sea sandstones with bubbled CO2 and saline solutions, at formation
temperatures. These concentration data were compared with produced water data from
current UK offshore hydrocarbon extraction activities.
The comparison showed that, taking the North Sea as a whole, the experimental results
fall within the range of concentrations of current oil and gas activities. However, on a
field-by-field basis, concentrations may be enhanced with CO2 storage, such that they are
higher than waters normally produced from a particular field. Lead, nickel and zinc showed
the greatest concentration increases in the experiments with the addition of CO2, with the
other five elements of interest not showing any strong trends with respect to enhanced
CO2.
The origin of the increased trace element concentrations was investigated using sequential
leaching experiments. A six step method of increasingly aggressive leaching was developed,
based on modification of methods outlined by Tessier et al. (1979) and Wigley et al. (2013),
to suit the North Sea sandstones used previously in the batch experiments. The extraction
method targeted water soluble elements, elements leached through desorption from mineral
surfaces, and elements released through the dissolution of carbonates, oxides, sulphides and
silicates.
From this experimental technique, trace element concentrations were classed as ‘mobile’
or ‘immobile’ under weak acid conditions of CO2 storage. The majority of elements were
classified as largely immobile. Using the batch experiment results we determined that
dissolution of carbonate and feldspar minerals was responsible for much of the observed
mobilised concentrations, although the abundance of these minerals was not a predictor for
absolute or relative concentrations.
References:
Tessier, A., Campbell, P. G. C., & Bisson, M. (1979). Sequential Extraction
Procedure for the Speciation of Particulate Trace Metals. Analytical Chemistry, 51(7),
844–851.
Wigley, M., Kampman, N., Chapman, H. J., Dubacq, B., & Bickle, M. J. (2013). In situ
redeposition of trace metals mobilized by CO2-charged brines. Geochemistry, Geophysics,
Geosystems, 14(5), 1321–1332. doi:10.1002/ggge.20104 |
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