The geothermal power plant of Soultz-sous-Forêts is producing 1.7 MWe gross power since 2016. The geothermal fluids discharged from one production well GPK-2, are simultaneously reinjected in two other deep reinjection wells, GPK-3 and GPK-4, within a deep crystalline fractured reservoir. In the framework of DESTRESS, a soft chemical stimulation methodology including risk assessment was defined and applied for enhancing the hydraulic performance of the well GPK-4. Thus, a chemical treatment was designed by using innovative chemicals which are able to dissolve secondary minerals sealing the natural fractures. For focusing the treatment, an innovative methodology was applied for injecting the chemicals via coiled tubing at great depth (5 km). Despite the realization of the stimulation of the GPK-4 well, the impact of the chemical treatment on the well injectivity was quite low and no real hydraulic improvement was observed. During this operation, the geochemistry of the fluids as well as the seismicity were monitored. Since 2016, induced seismicity has been monitored continuously during the geothermal exploitation: no felt seismic event was reported related to the various geothermal operations of the power plant.