This study was carried out within the framework of the European Hot Fractured Rock project in Soultz-sous-Forets, France. Due to the very high salinity of the brine contained in the fractured granite and the limited kinetic data for high temperature, a new code called FRACHEM has been developed to simulate the coupled thermal-hydraulic and chemical processes of flow in the fractured system. The goal is to forecast the long term behaviour of the reservoir under exploitation. Among the minerals taken into account for this simulation (calcite, dolomite, quartz and pyrite), carbonate reactions predominate. Their reaction rates are higher than the quartz and pyrite reaction rates. The amount of quartz and pyrite precipitated is neglected. As a consequence of calcite dissolution, the porosity increases at the injection point with resulting permeability changes. (C) 2003 CNR. Published by Elsevier Ltd. All rights reserved.