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| Titel |
COTHERM: Modelling fluid-rock interactions in Icelandic geothermal systems |
| VerfasserIn |
Bruno Thien, Georg Kosakowski, Dmitrii Kulik |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095175
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| Publikation (Nr.) |
 EGU/EGU2014-10622.pdf |
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| Zusammenfassung |
| Mineralogical alteration of reservoir rocks, driven by fluid circulation in natural or
enhanced geothermal systems, is likely to influence the long-term performance of
geothermal power generation. A key factor is the change of porosity due to dissolution
of primary minerals and precipitation of secondary phases. Porosity changes will
affect fluid circulation and solute transport, which, in turn, influence mineralogical
alteration.
This study is part of the Sinergia COTHERM project (COmbined hydrological,
geochemical and geophysical modeling of geotTHERMal systems) that is an integrative
research project aimed at improving our understanding of the sub-surface processes in
magmatically-driven natural geothermal systems. We model the mineralogical and porosity
evolution of Icelandic geothermal systems with 1D and 2D reactive transport models. These
geothermal systems are typically high enthalphy systems where a magmatic pluton is
located at a few kilometers depth. The shallow plutons increase the geothermal
gradient and trigger the circulation of hydrothermal waters with a steam cap forming
at shallow depth. We investigate two contrasting geothermal systems: Krafla, for
which the water recharge consists of meteoritic water; and Reykjanes, for which the
water recharge mainly consists of seawater. The initial rock composition is a fresh
basalt.
We use the GEM-Selektor geochemical modeling package [1] for calculation of
kinetically controlled mineral equilibria between the rock and the ingression water. We
consider basalt minerals dissolution kinetics according to Palandri & Kharaka [2]. Reactive
surface areas are assumed to be geometric surface areas, and are corrected using a
spherical-particle surface/mass relationship. For secondary minerals, we consider the
partial equilibrium assuming that the primary mineral dissolution is slow, and the
secondary mineral precipitation is fast. Comparison of our modeling results with the
mineralogical assemblages observed in the field by Gudmundsson & Arnorsson
[3] and by Icelandic partners of the COTHERM project suggests that the concept
of partial equilibrium with instantaneous precipitation of secondary minerals is
not sufficient to satisfactorily describe the experimental data. Considering kinetic
controls also for secondary minerals appears as indispensable to properly describe
the geothermal system evolution using a reactive transport modelling approach
[4].
[1] Kulik D.A., Wagner T., Dmytrieva S.V., Kosakowski G., Hingerl F.F., Chudnenko
K.V., Berner U., 2013. GEM-Selektor geochemical modeling package: revised algorithm and
GEMS3K numerical kernel for coupled simulation codes. Computational Geosciences 17,
1-24. http://gems.web.psi.ch.
[2] Palandri, J.L., Kharaka, Y.K., 2004. A compilation of rate parameters of water-mineral
interaction kinetics for application to geochemical modelling. U.S.Geological Survey, Menlo
Park, CA, pp. 1-64.
[3] Gudmundsson B.T., Arnorsson S., 2005. Secondary mineral-fluid equilibria in the
Krafla and Namafjall geothermal systems, Iceland. Applied Geochememistry 20,
1607-1625.
[4] Kosakowski, G., & Watanabe, N., 2013. OpenGeoSys-Gem: A numerical tool for
calculating geochemical and porosity changes in saturated and partially saturated media.
Physics and Chemistry of the Earth, Parts A/B/C. doi:10.1016/j.pce.2013.11.008 |
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