The Clermont-Ferrand basin, a part of the Limagne graben system is characterized by a geothermal anomaly with clastic reservoirs showing 100°C at 1.5 km depth. 3DGeoModeller (developed by BRGM) was used in the in order to build a 3D consistent geological model of the area. These studies were described earlier (see Calcagno et al., 2006).
In a second phase, the geothermal significance of the area is investigated. A full 3D unstructured Finite Element mesh is built using meshing capabilities from GEOWATT AG. This mesh is essentially based on the geological model provided by BRGM. Geological layers are discretized using hexahedra and prisms (3D elements). Faults are discretized using squares and triangles (2D elements).
A diffusive temperature model is applied, and temperature field is computed using the Finite Element code FRACTure (Kohl and Hopkirk, 1995). Different thermal properties are assigned to the various geological units. Thermal boundary conditions are derived from available data. Results of the model are compared with available temperature logs and the value of parameters is discussed and adjusted. Sections of the logging data from the two available boreholes Croix-Neyrat and Beaumont are well fitted, indicating local fluid movements along the other parts. This is in agreement with the hydrogeological description of the area.
As a final result, the total amount of geothermal energy available for each aquifer is computed, and the geothermal potential (recoverable energy) of each aquifer is mapped over the entire model. The most interesting geothermal target is identified (S1-DET); the total amount of recoverable energy in this aquifer is estimated to more than 500 PJ in the modeled area. The temperature model could be enhanced by better temperature data and a detailed analysis of hydrogeological behavior of the system in order to take in account advection processes in the numerical model.

References
Calcagno P., et al., 2006. How 3DGeoModeller helps to define and assess a geothermal reservoir: the Limagne case-study (French Massif Central). From Bruhn D. & Manzella A. (eds.) 2006, Proceedings of the Engine Workshop 1 "Defining, exploring, imaging and assessing reservoirs for potential heat exchange", 6-8 November 2006, Potsdam, Germany. ISBN 978-2-7159-2986-9. Orleans, BRGM Editions. Collection Actes/Proceedings. ISSN 1773-6161.
Kohl, T. and Hopkirk, R.J., 1995. "FRACTure" a simulation code for forced fluid flow and transport in fractured porous rock. Geothermics, 24(3): 345-359.

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