During the 1991 episode, two 50 hours hydraulic injection tests were carried out at the bottom of the well GPK1 (https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-GPK1). The fresh water was injected at a flowrate of 7 l/s during the first test and 15 l/s during the second test. New seismic probes composed of 3-axis accelerometers built by the CSM (Camborne School of Mines) monitored the induced seismicity. Two of them were deployed in new recovered wells 4550 (https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-4550) and 4601 (https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-4601). In addition, two hydrophones were installed in a new borehole EPS1 (https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-EPS1), drilled in 1990 and sited at about 600m SSE of GPK1. The network permitted to detect more than 400 induced seismic events during the two tests of the episode. About 60% of them were located. The following report from BRGM in the link gives details about the experiments and presents the results about the seismic monitoring and the location of the events. Some hydraulic data are presented as well with figures.

The Hot Dry Rock (HDR) site of Soultz-sous-Forêts in Alsace was chosen in 1986 for scientific investigations. During the first phase of the project (1987-1988), a first borehole GPK1 (https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-GPK1) was drilled. It reached a final depth of 2000 m and various investigations were undertaken during that period. In December 1988, an injection test was made at the bottom zone of this borehole with a relatively low flow rate of 3.3 l/s for a period of three days. Induced seismicity recorded was detected by 3-axis geophone probes deployed in three old recovered oil wells at depth ranging from 850 to 1350 m. A small amount of the detected seismicity could be located and showed a trend to grow towards greater depths than the injection zone. The following report from BRGM in the link gives details about the experiments and presents the results about the seismic monitoring and the location of the events. Some hydraulic data are presented as well with figures.

The 4601 well was an old oil well drilled in 1951. It has been deepened in the framework of the Soultz-sous-Forêts project from 1010m to 1604m. A seismic probe was deployed at the bottom of the well to monitor the microseismic activity induced by the several experiments conducted on the geothermal site of Soultz-sous-Forêts. Location of the 4601 wellhead (in WGS84): - Latitude: 48.92805654 | 48° 55' 41" N - Longitude: 7.84882476 | 7° 50' 55" E - Altitude: 169m

The 4616 well was an old oil well drilled in 1950-1951. The well was recovered and used as seismic observation well of the Soultz-sous-Forêts geothermal project from 1987. It has been deepened in the framework of the project to 1414m in 1990. Location of the 4616 wellhead (in Lambert coordinates): - Latitude: 48.93879707 | 48° 56' 19" N - Longitude: 7.86502087 | 7° 51' 54" E - Altitude: 155.4m

GPK3 well was drilled after GPK2 well in order to exploit a lower level at 5000 m depth, where the temperature reaches 200°C. GPK3 has been drilled in 2002 to build a triplet exchanger along ith GPK2 and GPK4 wells. It reaches a depth of 5090 m. Location GPK3 WGS84: Latitude: 48.93084122 | 48° 55' 51'' N Longitude: 7.86656943 | 7° 51' 59'' E

In order to improve the seismic monitoring of the Soultz-sous-Forêts geothermal site, a new seismic observation well was drilled in 2000. After two months of drilling, OPS4 reached the final depth of 1537m. Location of the OPS4 wellhead (in WGS84): - Latitude: 48.92108705 | 48° 55' 15" N - Longitude: 7.88306364 | 7° 52' 59" E - Altitude: 204m

In 1990/1991, an old oil well, EPS1 has been deepened and cored to characterize the granite reservoir and perform some deep hydraulic tests in view of a future experimental doublet. Unfortunately, the well had an important not controlled deviation and could not reach the expected depth. However, it was cored from 930 m to the bottom hole at 2227 m depth and provided a lot of scientific data. Location EPS1 WGS84: Latitude: 48.93118507 | 48° 55' 52'' N Longitude: 7.86766157 | 7° 52' 3'' E

GRT-2 is the second well drilled within the framework of the geothermal project ECOGI at Rittershoffen. The drilling of the well started in March 2014 and ended in July 2014. GRT-2 is a deviated well of 3196 m in length that reaches 2708 m TVD GL (true vertical depth from ground level) within the fractured granite basement. No reservoir enhancement was necessary at GRT-2. Production and circulation tests were realized from July to October 2014. The GRT-2 well is currently used as production well. It produces hot water at a temperature of 170 °C and with production flow rate of 70 L/s. Location of the GRT-2 wellhead (in WGS84): Latitude: 48.8970814354199° Longitude: 7.93865503246575°

GPK2 was the third well drilled for geothermal purposes at Soultz-sous-Forêts after GPK1 and EPS1. The well has been drilled southern to GPK1. It constitutes the second well of the doublet and obtains a maximum of fluid recovery. GPK2 well reached 3900 m in 1995 by drilling in destructive mode only. Hydraulic tests have been done to characterize the exchanger and to evaluate the potential fluid flow. In 1999, it was decided to exploit a lower level at 5000 m depth, where the temperature reaches 200°C in order to develop a geothermal resource aiming at electricity production? GPK2 was then extended to 5084 m. Location GPK2 WGS84: Latitude: 48.9308924 | 48° 55' 51'' N Longitude: 7.86662988 | 7° 51' 59'' E

The 4550 well was an old oil well drilled in 1949-1950. It has been deepened in the framework of the Soultz-sous-Forêts project from 1050m to 1500m in 1990. A seismic probe was deployed at the bottom of the well to monitor the microseismic activity induced by the geothermal site of Soultz-sous-Forêts. Location of the 4550 wellhead (in WGS84): - Latitude: 48.93750535 | 48° 56' 15" N - Longitude: 7.86972203 | 7° 52' 10" E - Altitude: 151m