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Hydraulic Stimulation and Geophysical Fracture Monitoring in the GeneSys-Project |
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The objective of the GeneSys-Project is to develop concepts for the geothermal
exploitation of low permeable sedimentary rocks. In a second step it also aims to
supply direct heat to the GeoCenter Hannover, located in the Northern German
Sedimentary Basin. Porosity and per-meability of the rocks at depth interesting for
geothermal use however, are too low to allow classical hydrothermal use. Therefore
concepts developed by EGS-projects in mainly crystal-line rocks need to be
transferred to the adjacent tight sedimentary rocks. The creation of large fracture
areas using the waterfrac technology is considered as the key challenge. To test
transferability, a 4100 m deep research well is operated in the Northern German
Sedimentary Basin. An extensive test program including massive waterfrac tests and
geophysical fracture monitoring has been carried out in the last years. Water fracs
tests were performed using un-treated freshwater. Injection rates went up to 50 l/s
at wellhead pressures of 330 bar during fracture propagation. Test analysis shows
that the tensile fracture that was created covers an area in the order of 100.000 m²
and has a vertical extension of approximately 200 m.
For microseismic fracture monitoring a network consisting of eight stations was
installed. At each station 4.5 Hz 3D geophones were installed in a 100 m deep well
and in addition seis-mometers were placed at the surface. Despite the detection
level of the network being low enough to detect events with magnitudes observed
during stimulation tests in crystalline rock (e.g. in Soultz project), only a very
low number of events was registered. Stress conditions suggest that shearing seems
to be unlikely. It is concluded that the propagation of the tensile fracture is
aseismic.
Measurements of the variation of the self-potential along two perpendicular profiles
in the vicinity of the well, and tiltmeter measurements along a profile completed
the geophysical fracture monitoring program. For the later methods a number of
methodological challenges were identified. Hence no direct information about
fracture geometry was derived.
For the stimulation of the well planned at the Hannover site, a microseismic network
will also be installed. Likewise more experience will be gained about the
stimulation process in low permeable sediments.
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Id: |
19 |
Place: |
Kartause Ittingen, Switzerland CH-8532 Warth TG
www.kartause.ch |
Starting date: |
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Duration: |
15' |
Primary Authors: |
ORZOL, Jens (GGA-Institute) |
Co-Authors: |
JUNG, Reinhard (GGA-Institute) BUNESS, Hermann (GGA-Institute) JATHO, Reiner (BGR) TISCHNER, Torsten (BGR) KEHRER, Peter (BGR) |
Presenters: |
ORZOL, Jens |
Material: |
Slides |
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