This work examines 3-D advective-conductive heat transfer during forced water circulation through fracturd crystalline rocks. The subject of the modelling investigation is the Hot-Dry-Rock (HDR) site at Soultz-Sous-Forets, Alsace, France. Fracture data from borehole logging provides an insight to the complex structure of crystalline rocks. The proposed model is based on the general idea, that flow and advective transport in stimulated HDR reservoirs occur mainly in fractures, whose orientation is linked by the tectonic stress field. Therefore, a deterministic fracture network model is established which represents the mean geometrical features of a stimulated HDR system.