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| Titel |
Potential environmental impacts of offshore UK 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 |
250134901
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| Publikation (Nr.) |
 EGU/EGU2016-15678.pdf |
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| Zusammenfassung |
| Geological carbon dioxide storage in the United Kingdom (UK) will almost certainly be
entirely offshore, with storage for over 100 years’ worth of UK CO2 output from
industry and power generation in offshore depleted hydrocarbon fields and sandstone
formations.
Storage capacity can be limited by the increase in formation water pressure upon CO2
injection, therefore removal and disposal of formation waters (‘produced waters’) can control
formation water pressures, and increase CO2 storage capacity. Formation waters could also
be produced during CO2-Enhanced Oil Recovery (CO2-EOR). The precedent from current
UK North Sea hydrocarbon extraction is to ‘overboard’ produced waters into the ocean,
under current regulations.
However, 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,
including heavy metals. Eight of these elements are specifically identified in the UK
as potentially hazardous to the marine environment (As, Cd, Cr, Cu, Hg, Ni, Pb,
Zn).
A comparison was made between the concentrations of these eight trace elements in the
results of laboratory batch leaching experiments of reservoir rock in CO2-rich saline solutions
and overboarded waters from current offshore UK hydrocarbon production. This 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. The analysis of the experimental results showed that prediction of trace
element release from sandstones with weak CO2-acid leaching is difficult. However, the
experiments did show that carbonate and feldspar mineral dissolution was a primary
source of these elements, where mobilised, regardless of their abundance within the
sandstone.
While the environmental risks associated with future offshore CO2 storage are considered
to be comparable with existing oil and gas operations, treatment of produced waters may be
required to reduce the trace element load and should be assessed on a field-by-field basis. |
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