Characterizing a decametre-scale granitic reservoir using ground-penetrating radar and seismic methods
<p>Ground-penetrating radar (GPR) and seismic imaging have proven to be important tools for the characterization of rock volumes. Both methods provide information about the physical rock mass properties and geological structures away from boreholes or tunnel walls. Here, we present the results...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-08-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/11/1441/2020/se-11-1441-2020.pdf |
| Summary: | <p>Ground-penetrating radar (GPR) and seismic imaging have
proven to be important tools for the characterization of rock volumes. Both
methods provide information about the physical rock mass properties and
geological structures away from boreholes or tunnel walls. Here, we present
the results from a geophysical characterization campaign that was conducted
as part of a decametre-scale hydraulic stimulation experiment in the
crystalline rock volume of the Grimsel Test Site (central Switzerland). For
this characterization experiment, we used tunnel-based GPR reflection
imaging as well as seismic travel-time tomography to investigate the volumes
between several tunnels and boreholes. The interpretation of the GPR data
with respect to geological structures is based on the unmigrated and
migrated images. For the tomographic analysis of the seismic first-arrival
travel-time data, we inverted for an anisotropic velocity model described by
the Thomsen parameters <span class="inline-formula"><i>v</i><sub>0</sub></span>, <span class="inline-formula"><i>ϵ</i></span> and <span class="inline-formula"><i>δ</i></span> to account for the
rock mass foliation. Subsequently, the GPR and seismic images were
interpreted in combination with the geological model of the test volume and
the known in situ stress states. We found that the ductile shear zones are
clearly imaged by GPR and show an increase in seismic anisotropy due to a
stronger foliation, while they are not visible in the <span class="inline-formula"><i>p</i></span>-wave (<span class="inline-formula"><i>v</i><sub>0</sub></span>)
velocity model. Regions of decreased seismic <span class="inline-formula"><i>p</i></span>-wave velocity, however,
correlate with regions of high fracture density. For geophysical
characterization of potential deep geothermal reservoirs, our results imply
that wireline-compatible borehole GPR should be considered for shear zone
characterization, and that seismic anisotropy and velocity information are
desirable to acquire in order to gain information about ductile shear zones
and fracture density, respectively.</p> |
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| ISSN: | 1869-9510 1869-9529 |