AN INTERPRETATION OF THE TRACER TEST IN A GEOTHERMAL TANK ON FRACTURED ROCK
The life span of a geothermal doublet in Hot Dry Rocks depends on the contact area through which the water extracts calories from the rock. The use of chemical tracers is of great interest to characterize the connection between the wells since the transfer of tracers takes place in the same fracture zones as the heat exchange while being much quicker. From the recovery curve of a perfect tracer one can deduce a "spreading function" which gives, among other things, the water - rock contact area. This function can be used also in prediction models for the thermal behaviour of the doublet. This methodology was applied on the site of the Geothermal Energy Project of the European Community Commission in Camborne (U.K.), in a joint project of the Camborne School of Mines, the Laboratoire de Geochimie Comparee et Systematique of Paris 6 University and the Centre d'Informatique Geologique of the Ecole des Mines de Paris. Tracers used and interpreted were Fluorescein and two EDTA complexes with Dysprosium and Ytterbium. Discrepancies in the volume found for the reservoir suggest a retention of Fluorescein. Simultaneously other Rare Earth - EDTA complexes presenting a retarding behaviour were injected, but the interpretation of these results was impossible due to analytical problems. These results confirm the interest of chemical tracers as a quick survey method giving informations on the evolution of the reservoir. However they show that a preliminary characterization of the exchanger structure is necessary for the results to be used in predictions of the "aging" of the doublet, and that possible retention mechanisms should be recognized and quantified through independent measurements.
Bibliographic Reference: EUR 10344 FR (1985) MF, 53 P., BFR 150, BLOW-UP COPY BFR 265, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989124123400 / Last updated on: 1987-01-01
Available languages: fr