Numerical
Flow Aanalysis
Geothermal Scanning for
Groundwater Flow
Geothermal methods to classify
the subsurface of Germany with respect to the
ability
for nuclear waste deposits.
Joint research project with
RWTH Aachen University and LIAG Hannover
funded by the German Federal Environment
Ministry (BMU) and the German Federal Office
for Radiation Protection (BfS).
The subsurface temperature increases with depth with
an average gradient of 30°C per kilometer.
Locally, strong deviations from this average
value can occur, resulting from following
factors:
Ground water flow: Water has a high
heat capacity. Even small ground water flows
(~ mm/a) can transport great quantities of
stored heat. Groundwater flow therefore might
result in a strong deformation of the
temperature field. The strongest effects are
observed in the surrounding of thermal springs
or gushing springs, which transport hot water
to the earth's surface.
Paleoclimate: During history of
earth the average surface temperature strongly
changed. These variations produce temperature
signals which are slowly transported with time
from earth's surface to greater depth. The
temperature increase after the end of the last
ice age is still measurable in boreholes of
1-2 km depth. Later events, such as the little
temperature drop at about the 15th century or
the warming within the last century are
detectable in boreholes of a few 100 m depth.
Subsurface heterogeneity: The thermal
properties of rocks strongly change depending
on the mineralogical composition and the rock
porosity. Thus the heat flow, having normally
a vertical direction, is refracted at bed
boundaries. To separate of effects of ground
water flow and paleoclimate from the
temperature field needs a good knowledge of
the thermal properties of the formations as
well as of their geometry.
By planning a conventional or a nuclear waste
deposit, one of the main targets is to protect
the environment from pollution. Pollutants can
easily be transported be streaming groundwater.
Therefore, main restrictions for nuclear waste
deposits are areas with ground water flow. The
objective of this study was to investigate
temperature profiles from boreholes in Germany
and to the separate all factors of subsurface
heterogeneities and paleoclimate from the
temperature logs in order to detect and
quantify of groundwater flow on a regional
scale.
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