RARE GAS ISOTOPE TRACERS IN GEOTHERMAL ENERGY.

Objectif

TO OBTAIN INFORMATION ON AN EUROPEAN SCALE ON THE INFLUENCE OF THE MANTLE ON HEAT FLOW AND ON THE CONCENTRATION OF NON-CONDENSIBLE GASES IN VARIOUS GEOTHERMAL RESERVOIRS. THE PROGRAMME AIMS TO EXPLOIT FURTHER THE USE OF RARE GASES FOR GEOTHERMAL ENERGY RESEARCH. EMPHASIS WILL BE PLACED ON RESERVOIR STUDIES.
A regional pattern of mantle helium-3 distribution in western Europe has been established through the analysis of helium isotopes in groundwaters, natural gases and geothermal fluids.
The most striking feature of this pattern is the clear relationship between tectonic setting and the presence or absence of mantle derived helium-3.

The contrasting tectonic situations in West Germany and adjacent areas provided some key insights into the release of mantle derived fluids into the continental crust.

The results both affirm the first order observation between active continental extension and presence of mantle derived helium-3 in the near surface. They clearly showed that the mantle helium-3 signature is distributed over wider geographic areas than surface volcanics, suggesting that melts are distributed over much broader regions at depth than at the surface. Of particular interest were the results from the Oberpfalz, which imply the presence of melts and mantle derived fluids at depth beneath the area, but without any other observable physical expression such as heat flow or seismicity.

A prelimenary examination of helium abundances and isotope composition in relation to groundwater chemistry, showed some important features. These included the association of the highest mantle derived helium signal with the lowest salinity, presumably shallow groundwaters in the East and West Eifel and Vogelsberg. In each of these regions the results approximated to a 2 component system in which 1 end member has a high salinity and high concentration of chlorine ions, associated with high total concentration of helium which is dominantly radiogenic with helium-4 of crustal origin. The other component had low salinity, low total concentration of helium and a high percentage of mantle derived helium-3. In each case, the end members appeared to be characteristic of relatively small geographic areas.

The mechanisms responsible for the transport of helium and other volatiles thr ough the crust are still poorly understood. Careful studies of rare gas isotopes in chemically well characterized groundwaters such as those described above offer a real possibility for advance. Given the comparitively straightforward relationship outlined, it should prove possible to characterize the chemistry of the fluids carrying the mantle helium signature into the groundwater. Coupled with information on groundwater ages and flow regimes, the rates of migration and accumulation of these components may be addressed.
THE OBJECTIVES OF THIS STUDY ARE:
1. THE DISTRIBUTION IN EUROPE.
THE AIM IS TO ACHIEVE A COVERAGE FOR HE-ISOTOPE DISTRIBUTION IN EUROPE COMPARABLE TO THAT AVAILABLE FOR HEATFLOW.
2. HDR AND HIGH ENTHALPY GEOTHERMAL ENERGY.
HELIUM ISOTOPES AND HEAVY RARE GAS ABUNDANCES WILL BE DETERMINED IN THE RETURN WATERS OF HDR PROJECTS AS WELL AS IN THE PRODUCTION WATERS OF HIGH ENTHALPY VENTURES.
3. HELIUM AS A GEOCHEMICAL/TECTONIC INDICATOR.
SAMPLES WILL BE COLLECTED IN COOPERATION WITH THE UNIVERSITIES OF ROME AND KARLSRUHE.
4. HEAVY RARE GAS ISOTOPES.
THESE STUDIES ARE ALSO PART OF 2. EMPHASIS WILL BE PLACED ON THE PHYSICAL PROCESSES THAT HAVE AFFECTED THE FLUID (SUCH AS BOILING).
THE FOLLOWING EQUIPMENT IS AVAILABLE FOR THIS PROJECT:
- MM-3000 DOUBLE COLLECTOR MASS-SPECTROMETER FOR 3HE/4HE RATIO MEASUREMENTS.
- RARE GAS EXTRACTION AND INLET SYSTEMS APPLICALBE TO WATER AND GAS SAMPLES.
12 CM RADIUS MAGNETIC SECTOR SINGLE COLLECTOR MASS SPECTROMETER WITH BAUER-SIGNER SOURCE FOR HEAVY RARE GAS ISOTOPE ANALYSIS.
- QUADRUPOLE (200 MASS RESOLUTION) AND INLET SYSTEM FOR DETERMINATION OF HEAVY RARE GAS ABUNDANCES IN GEOTHERMAL SAMPLES.
- APPROPRIATE CU-TUBE SAMPLING VESSELS.
ADVANCEMENT:
THIS CONTRACT IS A CONTINUATION OF CONTRACT EN3G0004. THE PRESENT STATE OF ADVANCE HAS BEEN DESCRIBED UNDER THAT HEADING.

Champ scientifique

Programme(s)

FP1-ENNONUC 3C - Research and development programme (EEC) in the field of Non-Nuclear Energy, 1985-1988

Thème(s)

Data not available

Appel à propositions

Data not available

Régime de financement

CSC - Cost-sharing contracts

Coordinateur

THE CHANCELLOR, MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE

Contribution de l’UE

Aucune donnée

Adresse

Trinity Lane, The Old Schools,
CB2 1TN CAMBRIDGE
Royaume-Uni

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