PHENOMENOLOGICAL STUDY OF TEMPERATURE GRADIENT ANOMALIES IN THE BUNTSANDSTEIN FORMATION, ABOVE THE SOULTZ GEOTHERMAL RESERVOIR, USING TOUGH2 SIMULATIONS

摘要

The geothermal reservoir at Soultz-sous-Forets occurs in a granite horst bounded by subvertical normal faults. Exploration and production results tend to show that the Buntsandstein formation, made of inter-bedded sandstones and argillite in the Rhine Graben, above the granitic basement, may also have geothermal potential. Indeed, temperature gradient anomalies observed in the Buntsandstein indicate that the Buntsandstein could be exploited to produce heat or even electricity. Anomalies of temperature gradient observed in wells could be explained by fluid flow patterns related to the faults. In order to validate this hypothesis, a phenomenological study was carried out using TOUGH2 to simulate fluid flow and heat transfer for various boundary conditions. The results of this study demonstrate that the anomalies could only be explained by lateral flows connecting two faults through three litho-stratigraphic levels identified as possible fluid circulation zones from petrophysical analyses. The differential of hydraulic potential gradient, from one fault to the other, required to allow geothermal fluids to flow inside the rock formation, can be explained by a structural dip of about 3°, consistent with observations at Soultz-sous-Forets.