After drilling GPK2 an extensive hydraulic program was performed in 1995 to test the well and the circulation with GPK1. The main tests were realized during June, July and August 1995. It consisted first of two injection tests at GPK2 in June. The injection tests revealed that the injectivity was too low to consider circulation between the two wells GPK1 and GPK2. A short term and a long term stimulation experiments were also performed in June at GPK2 to stimulate the fracture network. A total of 28000 m3 of fluid was injected during the long term experiment. Following the stimulations, a stepped post-fracturing injection test was realized to observe the results of the stimulations. Finally, three relatively short circulation experiments were performed in July and August by using GPK1 as production borehole and GPK2 as reinjection borehole.

Dates of the different tests of the 1995 hydraulic programme:

- First injection test at GPK2: from 11:26 11/06/95 to 01:50 12/06/95

- Second injection test at GPK2: from 11:56 12/06/95 to 23:11 12/06/95

- Short term stimulation experiment at GPK2: from 20:00 14/06/95 to 01:27 15/06/95

- Long term stimulation experiment at GPK2: from 10:24 17/06/95 to 16:03 28/06/95

- Stepped post-fracturing injection test at GPK2: from 08:08 01/07/95 to 20:02 02/07/95

- First circulation test between GPK1 and GPK2: from 08:35 09/07/95 to 21:32 24/07/95

- Second circulation test between GPK1 and GPK2: from 13:09 31/07/95 to 19:04 09/08/95

- Third circulation test between GPK1 and GPK2: from 04:50 16/08/95 to 19:19 20/08/95

Baumgärtner, J., Jung, R., Gérard, A., Baria, R. and Garnish, J., 1996.The European HDR project at Soultz-sous-Forêts: stimulation of the second deep well and first circulation experiments, Proceedings of the 21st Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California, January 22-24, 1996.

Gérard, A., Baumgärtner, J., Baria, R. and Jung, R., 1997. An attempt towards a conceptual model derived from 1993-1996 hydraulic operations at Soultz, Proceedings of the NEDO International Geothermal Symposium, Sendai, Japan, 11-12 March 1997.