1. Temperature profiles in geothermal systems L. Guillou-Frottier, BRGM, France Engine Launching Conference, February 14 th, 2006

2. > 2 Temperature profiles in geothermal systems > Examples > Heat conduction processes > Heat convection processes > Conclusion

3. > 3 Examples of temperature profiles Several distinct processes can create shallow thermal anomalies... After Muraoka et al., 2000

4. > 4 At least 4 possible causes - high heat producing granite - insulating cover - magma reservoir - hot fluids at shallow depths In these cases, the shallow thermal anomaly is not related to shallow convective processes.

5. > 5 > Role of an insulating (sedimentary) cover Case of Soultz-sous-Forêts (France) Pech. Dol. K + Mush Mush+Bund. Bund. Granite z 0 380 800 1000 1200 1400 Thermal conductivity 1.3 1.4 2.1 2.5 1.9 2.5 } T° profile in the upper part can be explained by thermal conductivity contrasts Schellschmidt & Clauser, 1996 Schellschmidt et al., 1997

6. > 6 > Role of a high heat production granite Grecksch et al., 2003 SOULTZ High heat production can also account for one part of the excess temperature

7. > 7 > Hypothesis of a cooling reservoir Case of Bouillante (Guadeloupe, French West Indies) Negative T° gradient ! BO-4 (1996)

8. > 8 > Hypothesis of a hot upwelling in a porous media T(z) = f(u, k, r, Cp, z)

9. > 9 Temperature profiles in a convective system Labioratory experiments by Guillou & Jaupart, 1995

10. > 10 Measurements of temperature profiles (lab. experiments) Profiles at different locations (above and near one upwelling) 3 zones can be defined : (1) the purely conductive zone = thermal boundary layer : high temperature gradient (2) zone of a decreasing T° gradient (3) zone of a small / null / negative T° gradient note the existence of negative T° gradients...

11. > 11 Local temperature profiles in geothermal systems Same observations as in convective systems : - 3 zones - local differences are constant over a large thickness Schellschmidt & Clauser, 1996

12. > 12 Up- and down-wellings can be inferred from local temperature profiles......however, drawing of isotherms is not sufficient to delineate the reservoir geometry...

13. > 13 Reservoir geometry and physical conditions could thus be better constrained by careful analyses of temperature profiles.

14. > 14 Conclusions parts > Simple 1D conductive models show that parts of vertical temperature profiles can be explained > Curved temperature profiles at shallow depths may result from combination of several processes > Scaling laws of thermal convection applied to temperature profiles may help in the characterization of geothermal systems