Image logs and the continuous coring of 8 geothermal wells in the Central Upper Rhine Graben (URG) are used for the structural characterization of 3 geothermal reservoirs at Soultz-sous-Forêts, Rittershoffen and Illkirch (France). The naturally permeable fracture zones (FZs) of the hard rocks are the targets of these wells. Subvertical natural fracture networks are striking NNW-SSE to N–S in the granite (inherited from the late-Variscan orogeny) and N–S/NNE-SSW in the sediments (mainly inherited from the Cenozoic era). The permeable fractures in the granite are subparallel to the main striking values. The fracture densities and thicknesses are the greatest in the first 500–1000 m of the granite. The fracture thickness surely reflects the intensity of the paleocirculations. The fracture distribution is governed by power laws and negative exponential laws. However, there is no simple relationship between those fracture properties and the present-day fracture permeability. The permeability is related to multiscale fracture networks channelling the fluids. Large-scale fractures within normal fault zones could be a more promising target than wide networks of distributed small-scale fractures affecting the whole granitic batholith. The geometry between the well trajectory and the fracture network, impacts also significantly the resulting permeability.

图像记录和上莱茵河上格拉本中部（URG）的8个地热井的连续取芯用于表征Soultz-sous-Forêts，Rittershoffen和Illkirch（法国）的3个地热储层。硬岩的自然渗透裂缝带（FZs）是这些井的目标。亚垂直的天然裂缝网络正向花岗岩中的ＮＳＷ向ＮＳ延伸（继承自后瓦里斯康造山运动），而沉积物中的ＮＳ ／ ＮＮＥＳＳＷ（主要来自新生代）。花岗岩中的渗透性裂缝与主要走向值不平行。在花岗岩的前500–1000 m处，裂缝的密度和厚度最大。裂缝厚度确实反映了古环流的强度。裂缝的分布受幂定律和负指数定律的控制。但是，这些断裂特性与当今的断裂渗透率之间没有简单的关系。渗透率与引导流体的多尺度裂缝网络有关。与影响整个花岗岩基岩的分布式小规模裂缝的广泛网络相比，正常断层带内的大规模裂缝可能是更有希望的目标。井眼轨迹和裂缝网络之间的几何形状也会显着影响最终的渗透率。与影响整个花岗岩基岩的分布式小规模裂缝的广泛网络相比，正常断层带内的大规模裂缝可能是更有希望的目标。井眼轨迹和裂缝网络之间的几何形状也会显着影响最终的渗透率。与影响整个花岗岩基岩的分布式小规模裂缝的广泛网络相比，正常断层带内的大规模裂缝可能是更有希望的目标。井眼轨迹和裂缝网络之间的几何形状也会显着影响最终的渗透率。