A geodetic study of the Soultz-sous-Forêts
and Rittershoffen geothermal sites
F. Masson, N. Gourmelen, C. Doubre, C. Heimlich
1
Abstract
Geothermal exploitation is often associated with surface deformation, which can reflect condition of
reservoir exploitation, reservoir properties and sub-surface instabilities. Quantification and
interpretation of surface deformation satisfies each of the 4 objectives of the LABEX G-EAUTHERMIE PROFONDE. The aim of our proposal is to quantify surface deformation above
geothermal systems along the Rhin Grabben.
The specific objectives are to (i) establish a long-term geodetic monitoring system, combining the
techniques of GPS and InSAR to maximise measurement accuracy, spatial and temporal resolution,
and (ii) to produce displacement time-series and mean velocity maps both at the scale of the
geothermal exploitation at Soultz-sous-Forêts and Rittershoffen and at the regional scale.
In 2013 and 2014, we established a network of GNSS station, acquired satellite observations,
investigated GNSS processing strategies, produced preliminary deformation time-series and mean
velocity maps and identified areas of surface deformation. In 2015 we will:
- extend our studied area to Strasbourg and the CUS to take into account the development of new
geothermal projects,
- develop real-time analysis of the GNSS and Insar data,
- analysis the displacement fields from models (mechanical models).
2 Progress report
2.1 GNSS
Realisation of the GNSS network
The aim of the second year was to finish the installation of the GNSS network around the two
geothermal plants of Soultz-sous-Forêts and Rittershoffen, and to develop the best processing strategy.
We have installed a new GNSS continuous station at GPK2.
Processing strategy
The data are processed with GAMIT/GLOBK software (Herring, King, & McClusky, 2010).
Results
Time series seems to indicate no or small movements. Small movements could be due to periodic
signal, which has to be confirmed using longer time series (figure 1).
2.2 InSAR
We have continued the acquisition of InSAR data along a track covering Soultz-sous-Forêts,
Rittershoffen and Landau. Several interesting results have been obtained.
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In the Soultz-sous-Forêts and Rittershoffen region. The figure 2 shows the displacements
obtained from InSAR in this region. The figure 1 is a comparison of the movements observed
from GPS and from InSAR. A very nice close correlation is observed validating the two tools
to follow the displacement.
In Landau, InSAR allows the monitoring of the event occurring at the geothermal plant (i.e.
large uplift around the geothermal plant (Heimlich et al., 2015)) (figure 3)
1 Figure 1: GPS and InSAR results at Rittershoffen. Top : InSAR. Bottom left : GPS. Bottom right : PS-InSAR. A clear
consistency is observed in GPS and InSAR movements.
Figure 2: InSAR results in the Soultz-sous-Forêts and Rittershoffen area.
2 Figure 3: PS-InSAR in Landau.
To summarize, two main results are obtained, which drive us for the future of the projet:
1- We are able to reveal very small movements, which are consistent in GPS and InSAR. The
detectable signal is below the mm. This indicates that small movements due to the variation of
mechanical properties of the geothermal reservoir could be monitored from surface
deformation. This point has to be explored.
2- We are able to reveal quickly problems of the geothermal plants which are not revealed by
seismology. To be more efficient, this has to be in real time.
These two main points are the keys of our project for 2015.
3 Proposal for 2015
3.1 GNSS
• The data acquisition is going on. And the processing strategy will be re-tested with the
increasing of the data acquisition. The station will be visited regularly, in order to control the
acquisition and save the data to prevent from some gaps in the data.
• The three GNSS stations of GPK1, GPK2 and ECOG will be connected to Internet to be
transmitted each day.
• A new processing strategy will be developed to get near real-time results using PPP (Precise
Point Positionning) strategy.
3.2 SAR
The objectives for 2015 are:
3 -
Further acquisition of Earth Observation dataset to consolidate the displacement time-series
around Soultz-sous-Forêt, Rittershoffen and Landau.
Acquisitions of data in the region of Strasbourg to develop the same strategy close to the
geothermal plants of the CUS
Moreover, we would like to investigate the possibility to use Sentinel data to develop a powerful tool
to create quickly maps of deformation. Financial support from the Idex of the Unistra has been
obtained in the framework of the A2S project. A postdoc will start to work on this subject in February.
A Master student will also work on this subject. End of 2015, we should be able to propose a robust
way to get deformation maps from Sentinel data. This solution is interesting because Sentinel data are
weekly and free. Nevertheless, Sentinel data and results of the processing need huge storage capacities.
We propose that the Labex supports these efforts financing storage capacities.
3.3 Modeling
We want to develop the modeling of the Landau geothermal powerplant deformation further than
presented in Heimlich et al. (2015). And we want to work together with the modeler team (V.
Magnenet et al.) to interpret our results in term of mechanic evolution of the reservoir (out of
catastrophic events).
3.4 Real-time strategy
We want to develop methodologies of acquisition and processing to go ahead to a real-time
monitoring of the geothermal sites. A new processing strategy will be developed to get near real-time
results using PPP (Precise Point Positionning) strategy. The advantage is to strongly simplify the
processing. To do this we would like to employ a ‘computer intership’ for 6 months (~3500€).
4 - Budget for 2015
GNSS
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•
•
•
•
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Missions for control and data search of the GPS stations (18 missions): 1500 €
battery for GNSS: 400 €
external computer storage : 240 €
1 missions to EGU meeting in 2015: 1500 €
1 missions to AGU meeting in 2015: 2500 €
internship : 3500€
Total: 9640 €
SAR
•
•
100 images at €160 / image: €16000
Storage for TerraSAR X and Sentinel data (raw data + processing): 20TB backed-up ->€6000
(€300/TB/yr)
Total: €22000
TOTAL: 31640 € (unused amount in 2014 : 13000 – Needed : ~18640). 4