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Defining, exploring, imaging and assessing reservoirs for potential heat exchange - Potsdam, Germany, Workshop1
Defining, exploring, imaging and assessing reservoirs for potential heat exchange - Potsdam, Germany, Workshop1
6-8 November 2006 GeoForschungsZentrum Potsdam (GFZ)
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Location of anomalously hot temperatures due to heat refraction
To explain temperature differences at a given depth, several mechanisms can be 
invoked. In volcanic areas, magma chambers heat the overlying crust and several 
hundreds of °C may be expected at a few kms depth. Outside these regions, variations 
in mantle heat flow can trigger differences in crustal temperatures, but they only 
act over several tens to hundreds of kms. At a smaller scale, temperature 
differences at shallow depths can only be explained by crustal heterogeneities 
and/or fluid flows. When fluid motion is negligible, heat transfer processes  and 
thus subsurface temperatures  are basically controlled by thermal properties of 
rocks (mainly thermal conductivity and heat production rates). Actually, because of 
the heterogeneous nature of the crust, one can say that heat refraction occurs 
everywhere as soon as the working scale is comparable with typical lengths of 
crustal bodies (layer thicknesses, granitoids sizes, etc). 
Results from thermal modelling of heat refraction allow to quantify simple effects 
due to crustal heterogenities, and thus may be compared with real data (heat flow 
measurements and/or temperature profiles). However, some subtle additional 
parameters, like the geometry of the heterogeneity, appear to play a significant 
role in the interpretation of field data. In particular, an anomalous conductive 
body with a small aspect ratio (width over depth) will not disturb the underlying 
isotherms even if a high surface heat flow is measured (e.g. heat flow anomaly in 
Manitoba). On the opposite, one may easily miss a large-scale temperature anomaly 
when a large aspect ratio insulating body is considered, because surface heat flow 
is only affected at the very edges of the heterogeneity (e.g. sedimentary basins, 
ash-flow calderas). The case of one sedimentary basin in south France will be 
discussed. Other heat refraction effects associated with contrasts in heat 
production, or with depth-dependent thermal conductivity, will be presented. 
Nevertheless, knowledge and measurements of appropriate thermal properties remain 
unavoidable as soon as theoretical and modelling results are performed to locate 
potential geothermal reservoirs.
Id: 3
Place: GeoForschungsZentrum Potsdam (GFZ)
14473 Potsdam, Telegrafenberg
Starting date:
06-Nov-2006   10:05
Duration: 03'
Contribution type: Poster
Primary Authors: Dr. GUILLOU-FROTTIER, Laurent (BRGM)
Presenters: Dr. GUILLOU-FROTTIER, Laurent
Material: slides Slides
poster Poster

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