The Soultz-sous-Forêts geothermal plant in northern Alsace (France) is under consideration for a campaign to actively stimulate the low-permeability granitic reservoir. The operation of the enhanced geothermal system requires the re-injection of fluid into the geothermal reservoir, which can cause a strong disequilibrium between the fluid and the granitic rock, as well as the possible dissolution/precipitation of minerals. These mineralogical transformations may have a significant impact on porosity, permeability and fluid pathways in the geothermal reservoir. Various studies have reported that the hydraulic connection between the injection well and the production well is quite poor. Therefore, chemical stimulations are necessary to increase the productivity and injectivity of the Soultz geothermal system. Before performing chemical stimulation in the Soultz geothermal system, a modelling approach is considered to discuss different scenarios in terms of the choice of acid and the amount and duration of acid injection. The approach used in this work is based on the geochemical code KIRMAT, which enables us to represent the geothermal reservoir using single-porosity and double-porosity models. The code evaluates the changes in the porosity and permeability of the Soultz reservoir based on the evolution of all primary and secondary minerals as a function of time in the geothermal system. The modelling results showed that chemical stimulation could significantly increase porosity and perme-ability; however, for both single and double-porosity models, the improved zones are very limited and are only present within a few meters of the reinjection well. The modelling results obtained from the sensitivity case studies showed the significant impact of the Darcy velocity, the initial concentration of the acid used, the duration of the injection and the initial calcite amount, especially in regard to the changes in porosity and the mineralogical transformation of the zone around the acid-injected well. Higher concentrations of the HCl solution also increase the dissolution of primary minerals and then exhibit a stronger porosity increase in the zone around the injection well, but further, precipitation reduces the positive achievements of chemical stimulation.