Temperature profiles in geothermal systems L GuillouFrottier BRGM

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

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

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

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. 4

> Role of an insulating (sedimentary) cover Case of Soultz-sous-Forêts (France) Thermal conductivity z Pech. 0 1. 3 380 Dol. K + Mush+Bund. Granite 1. 4 800 } 2. 1 1000 1200 1400 2. 5 1. 9 2. 5 Schellschmidt et al. , 1997 T° profile in the upper part can be explained by thermal conductivity contrasts Schellschmidt & Clauser, 1996 5

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

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

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

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

Measurements of temperature profiles (lab. experiments) 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. . . Profiles at different locations (above and near one upwelling) 10

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

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

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

Conclusions > Simple 1 D 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 14