Heat extraction from deep rocks at Soultz-sous-Forets

A European coordinated research program for the study of hot-dry-rock systems is in progress at Soultz-sous-Forets (Alsace, France). The aim of this project is the extraction of heat from the granite batholiths distributed along the Rhine graben. The technique used involves important forced water circulations under relatively low-pressures using the natural geologic fractures network. The region concerned extends about 3000 km2 under both the French and the German territories. The program started in 1987 with preliminary scientific investigations followed by a feasibility study. In December 1995, two deep wells, GPK1 (3600 m) and GPK2 (3900 m) were available and equipped for hydraulic testing. Temperatures encountered can reach 168 C at 3800 m with a geothermal gradient exceeding 3.5 C/100 m below 3600 m. The tests performed have shown that the hydraulic performances of these wells can be considerably improved using a simple well stimulation technique. (J.S.). 1 fig