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

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

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 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

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