The results observed during the past twenty years at Soultz demonstrated 
that “usual” hydraulic stimulation techniques when applied in such an 
hydrothermal/tectonic context can provide both real, but unfortunately limited, 
improvements of the wells hydraulic performances and real, but fortunately up to now 
limited, microseismic nuisances. Seven major hydraulic stimulation tests performed 
at Soultz generated always large “microseismic clouds” but quite variable 
improvement of the wells hydraulic performances.

The questions about the possible usefulness of that induced microseismicity in the 
situation of Soultz came to light progressively. Despite all efforts and very 
large “microseismic clouds” the hydraulic results from the stimulation tests up to 
now resulted in injectivity indexes which were limited within a range 3 to 5 l/s/MPa 
(target being 10 to 20). 
Those questions became definitely unavoidable after the stimulation of the well GPK3 
performed at Soultz in 2003 at depth ~4750m. During that test (including a dual 
stimulation with a second well) ~34 000 m3 of water where injected in GPK3 at mean 
flow ~50 l/s generating ~90 000 events [among which 39 of magnitudes high enough 
(1.9
                                        

CH-8532 Warth TG
www.kartause.ch