Characterization of fracture network based on photogrammetry
Résumé
Nowadays, deep geothermal exploitation projects in France are mostly localized in deep fractured geological contexts as rift basins. This study contributes to a project aimed at developing a theoretical model of geothermal reservoirs in fault zone in rift areas (grabens) such as the SouthEast Basin of France. The knowledge of the fracture network and the structural characterization of the potential geothermal reservoirs is essential to the development of a thermo-hydro-mechanical model. The orientation and spatial organization of the fracture networks in the targeted sedimentary formations have been studied from virtual outcrop models acquired using photogrammetry. The results have shown that most fractures observed on the outcrop level are oriented in accordance with the 1:50 000 map faults orientation, i.e. NW-SE to NNW-SSE. These local faults are related to the geodynamics events that occurred during the Valence Basin tectonic evolution such as those developed during the Tethysian rifting. The fractures frequency increases with closeness to these main faults. In the first 5 meters from the fault, the fractures are grouped together as a corridor, with a mean spacing S of 25 cm. After that, fractures are regularly located but more spaced (S > 50 cm) over several tens meters on both sides of the fault. All these information can therefore be used as input parameters to the thermo-hydro-mechanical modelling of the geothermal reservoir in order to characterize fluid circulations, heat transfer and to predict the mechanical behavior during the exploitation. The work conducted in this study also revealed the usefulness and relevance of the use of photogrammetry in analyzing fracture networks at the outcrop level. The virtual outcrop models delivered reliable and complementary measurements to those carried out directly on the field.
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