| Title | From Geological Interpretation and 3D Modelling to the Characterization of the Deep Seated EGS Reservoir of Soultz (France). |
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| Authors | Sausse J., Dezayes C., Genter, A. |
| Year | 2007 |
| Conference | European Geothermal Conference |
| Keywords | 3D fracture network, reservoir characterization, Soultz-sous-For?ts |
| Abstract | This study presents a 3D interpretation of the geophysical logs run after the drill of three wells at 5 km depth in the framework of the Soultz European EGS (Enhanced Geothermal Systems) project. The major fracture zones encountered in these wells are characterized through examination of borehole image logs, classical geophysical well logs and cutting samples. In the open holes of the granite massif, the flow logs and temperature profiles allow to distinguish natural flowing fractures. These large-scale fracture zones are characterized by sealed core and an around damage zone that is highly fractured and therefore highly permeable. The fractures are identified and measured in orientation and in dip by borehole imagery techniques. The major issue for reconstructing the 3D geometry of the Soultz fracture network is the question of the fracture extension. In a first approach, we define and correlate the fracture extensions according to the importance of flow observed on flow log runs during the injection and stimulation tests in the wells. A maximal fracture extension of 600 m length is proposed, excepted for the most important fault zone that extends to 2000 m. This geometry seems to be in agreement with the development of microseismicity within these fracture planes during the 1997-2003 hydraulic stimulation phases at Soultz. The model is enclosed in a 3D regular grid. The grid axes fit on the directions of the maximal anisotropy of the microseismic cloud (N170?E). The main fractures are modeled by planar discs centered on the wells respecting the fracture orientations and widths. Moreover, each plane is characterized by a property corresponding to its permeability assumed as proportional to the importance of the flow developed in the vicinity of the fracture zones. Storage capacities and types of permeability are quantified. They are similar for the production wells but strongly different for the injection well. The 3D well connectivity is modeled and discussed. This geological model could be used as a geometrical basis for fracture quantification of fracture porosity and permeability in the EGS reservoir. |