Transcript Slides

Temperature profiles in
geothermal systems
L. Guillou-Frottier, BRGM, France
Engine Launching Conference, February 14th, 2006
Temperature profiles in geothermal systems
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Examples
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Heat conduction processes
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Heat convection processes
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Conclusion
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Examples of temperature profiles
After Muraoka et al., 2000
Several distinct processes can create shallow thermal anomalies...
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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.
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> Role of an insulating (sedimentary) cover
Case of Soultz-sous-Forêts (France)
Thermal
conductivity
z
Pech.
0
1.3
380
Dol.
1.4
K + Mush
Mush+Bund.
800
}
2.1
1000
2.5
1200
Bund.
1.9
1400
Granite
2.5
Schellschmidt et al., 1997
T° profile in the upper part can be
explained by thermal conductivity contrasts
Schellschmidt & Clauser, 1996
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> 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
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> Hypothesis of a cooling reservoir
Case of Bouillante (Guadeloupe, French West Indies)
BO-4
(1996)
Negative T° gradient !
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> Hypothesis of a hot upwelling in a porous media
T(z) = f(u, k, r, Cp, z)
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Temperature profiles in a convective system
Labioratory experiments by Guillou & Jaupart, 1995
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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)
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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
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Up- and down-wellings can be inferred from local temperature profiles...
...however, drawing of isotherms is not sufficient
to delineate the reservoir geometry...
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Reservoir geometry and physical conditions could thus be better constrained
by careful analyses of temperature profiles.
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Conclusions
> 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
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