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| Titel |
Expected fluid residence times, thermal breakthrough, and tracer test design for characterizing a hydrothermal system in the Upper Rhine Rift Valley |
| VerfasserIn |
I. Ghergut, J. Meixner, D. Rettenmaier, F. Maier, M. Nottebohm, T. Ptak, M. Sauter |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250071085
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| Zusammenfassung |
| Relying on the structural-hydrogeological model proposed by J. Meixner (2009) for a
particular hydrothermal system in South-West Germany (on the East side of the Upper Rhine
Rift, this reservoir being used to demonstrate electricity production by means of a well
doublet), we set up a distributed-parameter model (using Feflow) enabling to numerically
simulate fluid ages, temperature evolutions and tracer test signals for a number of contrasting
assumptions w. r. to
(a) the nature of boundary conditions and hydrogeological characteristics of
remotely situated, large-scale natural faults,
(b) the degree of permeability contrast between different system compartments,
(c) the hydrogeological characteristics of a naturally-occurring fault, located
between injection and production wells.
It appears that a spike dimensioning allowing for tracer signals to become detectable during the
first three years after tracer injection in all of the contrasting a/b/c scenarios is not feasible in
practice. In some of the a/b/c cases considered, the system will act like a very large reservoir,
with fluid residence times in the order of decades, and extreme dilution of injected tracers.
Even using preparative-scale cleaning of samples, brine separation, sample enrichment by
solid phase extraction, evaporative concentrating etc. followed by state-of-the-art
chromatography techniques to separate between tracer and natural background, it will not be
possible to lower tracer detection limits below a certain threshold, which is mainly dictated
by the amount of certain naturally-occurring aromatics in the reservoir fluids. On practical
reasons, the spike dimensioning will be limited to some hundred kilogram of one or
two organic tracers. This implies that part of the above-mentioned, contrasting
a/b/c scenarios will remain indistinguishable during the first three years after tracer
injection.
However, for this reservoir structure, there is not a bijective correspondence between
early-vs.-late appearance of tracer and small-vs.-large reservoir. Therefore, we further
examine the questions:
How much information will be lost, and what degree of uncertainty will affect
temperature predictions, as a consequence of the chosen practical ceiling on
injected tracer quantities?
Can single-well, dual-tracer push-pull tests (to be conducted at the geothermal
re-injection and/or at the geothermal production well) contribute to reducing the
ambiguity of inter-well early-signal inversion?
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Acknowledgement: This work pertains to a research project jointly funded by Energie
Baden-Württemberg (EnBW) and by the German Federal Ministry for the Environment,
Nature Conservation and Nuclear Safety (BMU, project key: 0325111B), with operational
support from local Energy and Water Supply Plants (EWB), from the Karlsruhe Institute of
Technology (KIT, Hydrogeology Group), and from the European Institute for Energy
Research (EIfER, Dr. Zorn). |
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