Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Geothermal Energy:
Unlimited, Environmental-Friendly, and Economic
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Everywhere in the earth‘s
crust, the temperature
increases with depth. For
example, in parts of
Germany the temperature
at 3 km depth is 120-
180C.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
A greenhouse A swimming pool
An electric power stationThe heat stored in the rocks at
depth can be used for direct
heating, electricity production,
or both.
Source: Orkustofnun
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
The hot springStrokkur inIceland.
For economic use of the heat stored in the rocks, detailed geological
studies are absolutely necessary – even in areas such as Iceland
where geothermal fields are common at the surface.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Geothermal use of hot-dry
rocks requires:
• a hole for injecting cold water;
• a stimulated, fractured reservoir;
• a hole for producing hot water;
• and a power plant.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
To assess the geothermal potential of an area, we must make
a) detailed geological and geophysical site studies,
b) laboratory tests and studies, and
c) numerical models.
a
b c
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
To minimise the risk and maximise the chance of success in
geothermal projects, we begin by geological field studies. For
example, we study extinct palaeogeothermal fields to understand
current geothermal fields.
Part of a palaeogeothermal field in sedimentary rocks in England.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
To understand the
permeability of a fractured
geothermal reservoir, the
host-rock fracture system
must be known. Here is a part
of a fracture system in the
Bunter Sandstone, Göttingen.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Much geothermal water
is transported along
faults, such as this one
in the Muschelkalk in
Göttingen.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
The permeability of a geothermal
reservoir in a fault zone depends
partly on the fracture systems and
properties of the fault zone, and
partly on the local stress field.
Field example from England.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
An extinct geothermal system, consisting of mineral
veins, in a fault zone in Iceland.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Field studies must be complemented by laboratory studies of samples
from the potential reservoir rocks to determine their properties.
Strength tests
Scanning-electron microscopy
Texture analyses
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
H
P
h
P
Hh
Laboratory experiments on rock samples can be used to
determine their permeabilities and how these relate to local
stress fields and the fabric of the rock.
Stress-dependent permeability Fabric-dependent permeability
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Field and laboratory studies should be complemented by numerical models
to forecast fracture propagation, interconnection, and fluid transport in the
potential reservoir. These studies are also necessary for deciding on the
type of stimulation needed to increase the reservoir permeability.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Example of a simple
numerical model showing
the propagation, through
many crustal layers, of a
vertical fluid-driven fracture,
that is, a hydrofracture.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Numerical models on the stress concentration (left) and direction of
hydrofracture propagation (right). The thin layers are soft, the thick layers
are stiff. This difference in mechanical properties between the layers
largely controls whether, and in which direction, a hydrofracture
propagates.
Tensile stress concentration Direction of hydrofracture propagation
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Based on the geological and geophysical investigations, a site is
selected and the type of stimulation needed for the reservoir
determined. The two basic stimulation methods are (a) hydraulic
fracturing, and (b) massive hydraulic stimulation.
Source: BGR
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Source: Smith & Shlyapobersky 2000
In hydraulic fracturing, a fluid under high pressure is injected into a
certain layer – the reservoir. The fluid creates a fracture that increases
the permeability of the reservoir.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
In a massive hydraulic
stimulation, natural fractures
slip and open up, thereby
generating a high-permeability
reservoir between the injection
and production drillholes. The
fracture slip is monitored
through numerous very small
earthquakes (shown here by
hypocentres).
Source: Asanuma et al. 2002(Tohoku University, Japan)
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Vin Vout
Injection phase
Tracer 1, Tracer 2
Production phase
Diffusion front(immobile water)
Pulse-input
Back diffusion
Following the geological studies, the numerical modelling, and the
stimulation experiments, tracers are used to test the permeability of the
reservoir.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Tracer tests also provide information on the contact area between the
fractures and the surrounding rock in the resevoir, and thus how
effectively heat is transported from the rock to the water.
Tracer-Tests in Bad Urach
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Source: Geoforschungszentrum Potsdam
Large parts of Germany (here indicated by light-green colour) offer suitable sites for man-made geothermal reservoirs. Some current geothermal drilling sites are indicated by large red dots.
Groß Schönebeck
Hamburg
Hannover
ThüringischesBecken
Ober-rhein
graben
Dresden
Leipzig
Urach
SoultzStuttgart
Frankfurt
Köln
Erding
Straubing
BayerischesMolassebecken
NorddeutschesBecken
Neustadt-Glewe
BerlinGenesys Horstberg
Basel
Speyer
Offenbach
Pullach
Unterhaching
Aachen
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Some 14% of the
worldwide primary
energy consumption is
provided by renewable
sources. It is predicted
that non-renewable
energy sources start
to decline in the first
half of this century.
Source: Shell
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
• For many decades now, there has been commercial production of electricity and direct use of geothermal energy at the scale of hundreds of mega-watts.
• More than 20 countries worldwide use geothermal steam to produce electricity. In several countries, 10-22% of the total electricity production is from geothermal sources.
Photograph: a drillhole providing steam for the geothermal power plant at Nesjavellir, Iceland.
Source: Fridleifsson 2002
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Conclusions
The experience from Iceland and other countries is of help when assessing the potential of geothermal-energy use in Germany.
Heat gradients in parts of Germany are similar to those in the older parts of Iceland, and thus quite high.
Trial-and-error methods in geothermal exploration are not used in Iceland and unlikely to be successful in Germany.
The main unknown scientific parameter for man-made reservoirs is the fracture-related permeability.
The permeability can be inferred from field data, natural analogies, laboratory and site tests, and numerical models.
Hannover-Messe 2005
G GZ GEOWISSENSCHAFTLICHESGEOWISSENSCHAFTLICHESZENTRUM GÖTTINGENZENTRUM GÖTTINGEN
Geothermal power plants are environmental-friendly,
and their surroundings can be used for various purposes. Example: the Blue Lagoon in Iceland.