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.

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.

VDH-GT1 is the first well drilled within the framework of the Geoven geothermal project at Vendenheim. The drilling of the well began in June 2017 and reached a final length of 5408 m in March 2018. A second leg at VDH-GT1 was drilled between February and September 2019 and a third between June and August 2020 to 5447 m (4644m TVD). VDH-GT1 will be used as production well. Location of the VDH-GT1 wellhead (in WGS84): Latitude: 48.8970080 Longitude: 7.9387218 Altitude: 134m At the present time, the Geoven project (https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/VDHD) is still in development and this description may change.

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

GPK4 well was drilled after GPK3 well in order to exploit a lower level at 5000 m depth, where the temperature reaches 200°C. GPK4 has been drilled in 2004 to build a triplet exchanger along ith GPK2 and GPK3 wells. It reaches a depth of 5260 m. Location GPK4 WGS84: Latitude: 48.93079836 | 48° 55' 50'' N Longitude: 7.86652359 | 7° 51' 59'' E

GPK1 was the first well drilled for geothermal purposes at Soultz-sous-Forêts. The well was first drilled in 1987. It reached 2000 m and the temperature at the bottom hole was 140°C. Several hydraulic injections have been done associated with tracer tests and temperature and flow logs. In order to get deeper information, the GPK1 well was deepened to 3600 m in 1992. The downhole temperature reached 160°C. Location GPK1 WGS84: Latitude: 48.93525543 | 48° 56' 6'' N Longitude: 7.86535117 | 7° 51' 55'' E

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

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

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

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