Environmental Engineering Reference
In-Depth Information
Regions like Central Europe that are not near the borders of tectonic plates do not
have optimal geothermal resources. This does not mean that high temperatures do
not exist underground. However, compared to regions like Iceland where geother-
mal conditions are favourable, it takes drilling at greater depths to reach the same
The best geothermal conditions in Germany are in the lowland plains of the Rhine
(Figure 10.4). In this region temperatures of 150 °C or more can be found at depths
of 3000 m. The average thermal depth gradient is around 3 °C per 100 m. On this
basis, a temperature increase of 90 °C could be expected at depths of 3000 m. In
Iceland temperatures like this occur at depths of just a few hundred metres.
Figure 10.4 Temperatures in Germany at depths of 1000 m and 3000 m. Graphics: www.liag-hannover.de
(Schellschmidt et al. , 2002).
Deep drilling is required to exploit the high temperatures. The technique for this
type of drilling has long been familiar from oil extraction. Rotary drilling methods
are employed, whereby motors drive a diamond bit into the depth. At very great
depths, a drill bit cannot be driven in the conventional way over a drill string due
to the increased strain caused by turning and friction. An electric motor or turbine
therefore directly drives the drill bit.
The actual derrick (Figure 10.5) that holds the drill pipe is all that can be seen
from the surface. Water is pressed into the borehole at pressures of up to 300
bars through the inside of the driller. This fl ushing of the mud forces crushed rock
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