 |
| Titel |
A multi-tracer approach for the exploration of deep geothermal energy potential and fault zone characterisation, applied in the Upper Rhine Graben |
| VerfasserIn |
Florian Freundt, Sami Al Najem, Werner Aeschbach-Hertig, Margot Isenbeck-Schröter, Gerhard Schmidt, René Grobe, Michael Kraml |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097471
|
| Publikation (Nr.) |
 EGU/EGU2014-13059.pdf |
|
|
|
|
|
| Zusammenfassung |
| Current methods of geothermal exploration rely on various expensive geophysical
methods (e.g. 3D reflection seismics) to identify permeable fault zones and the
geometry of geothermal aquifers. However this analysis alone does not allow for an
estimation of an active fault’s hydraulic permeability nor provides a characterisation of
the chemical properties of the deep aquifer fluid. Both factors play an important
role in optimising siting of geothermal wells and operation of a geothermal power
plant.
This work presents a low cost strategy characterizing deep hydrogeochemical reservoirs
using a combination of methods from hydrogeochemistry and isotope hydrology in hot
springs and near surface groundwater. The main goal is to confine the area of interest for
further, indirect geophysical investigation. For this purpose natural geochemical and
isotopical tracers as well as rare earth elements, 3He/4He ratios, and radiogenic isotopes (Sr
and Pb) are investigated.
Data from the first sampling campaign in the northern Upper Rhine Graben, close to
Groß-Gerau, Germany, shows promising results, indicating an area of increased interest
where elevated helium ratios coincide with characteristic geochemical data, fault location and
a previously known saltwater anomaly. Geochemical analyses exhibit three different types
of fluids and various mixtures. CaHCO3-dominated waters represent Quaternary
aquifer conditions whereas MgSO4-dominated waters are characterised by a Tertiary
aquifer rock. Higher saline NaCl-dominated waters show an impact of mantle fluids
revealed by 3He/4He isotope analysis. The ratio is highest where the main fault of
the northern Upper Rhine Graben crosses the Rhine river. This suggests that the
fault is hydraulically active and connects ascending deep fluids with the shallow
aquifer.
Further investigations of rare earth element patterns as well as radiogenic isotopes will
identify the origin, the ascent as well as the retention time of the deep fluids more precisely.
Water-rock interactions and mixtures of different fluids in the reservoir and during the ascent
are estimated and simulated using geochemical and hydraulic models. Thus, the geometry of
the aquifer, the temperature, the quantity and the quality of the ascending deep fluid in the
reservoir is estimated. The retention time is a good indicator for the deep fluid being part of a
fossil reservoir or being recharged naturally. The Upper Rhine Graben was chosen to
test the multi-tracer method due to its well-studied geology and some significant
preexisting geophysical data to allow for comparison and validation of the study’s
findings. The aim is to identify the most useful tracers of deep geothermal fluid
circulation, which consecutively can be applied to other regions with less prior
information. |
|
|
|
|
|
|