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| Titel |
Isotope mass balances in deep formations: How to consider the influence of pressure, temperature and salinity |
| VerfasserIn |
Veith Becker, Anssi Myrttinen, Johannes A. C. Barth |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042923
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| Zusammenfassung |
| Stable carbon isotopes are a sensitive tool to trace migration and to quantify mixing of CO2
from different sources. This technique is well described for application at the surface and
under close-to-surface conditions. However, in order to use isotope mass balances when
monitoring the fate of CO2 at carbon storage sites, some distinctive characteristics of deep
formations have to be considered. High pressures (from 30 to 200 bar), temperatures (up to
over 120 Ë C) and salinities (approx. 100 to 400 g/L) influence the carbonate equilibrium as
activities, fugacities and the stoichiometric equilibrium constants (fCO2, Kcalcite*, K1*, K2*)
change with these parameters. Furthermore, isotopic fractionation is also affected by
these parameters. Various relations are published, describing these dependencies
with approaches of different complexity and exactness. In this field of application,
available sampling data is usually limited, so that averaging and interpolation of
input data may lead to noticeable error ranges. Under these conditions, the most
elaborated algorithms do not necessarily perform better than more simple ones with
respect to the overall error of the calculations. This work therefore compares the
available approaches to describe temperature, pressure and salinity dependence in
carbonate equilibrium calculations, as well as carbon isotope fractionation in this
process with respect to the best ratio of accuracy in carbon storage site monitoring
applications.
It stands out that the fugacity and the stoichiometric constants involved in DIC-speciation
are heavily influenced by pressure, temperature and salinity in general, whereas the individual
composition of the solution may be simplified, at least for NaCl-type brines. With respect to
fractionation, temperature plays a key role; pressure and salinity variations contribute to the
species distribution only to a small amount.
This study was conducted as a part of the R&D programme CLEAN, which is funded by
the German Federal Ministry of Education in the framework of the programme
GEOTECHNOLOGIEN. |
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