  A wide range of geophysical methods is used for the exploration of deep
geothermal resources. It aimsat characterizing the deep fractured network and
its capacity for fluid/heat extraction. This relieshowever on the capacity of
geophysical techniques to 1) image the geometry of the fractured networkbut
also 2) characterize the petro-physical properties of the fracture network and
matrix. The challengeis however that the geophysical inverse problem is
ill-posed and multi-scale.To overcome these challenges, we propose here to take
a multi-physics and multi-scale approach of thegeophysical/petro-physical
inverse problem. To do so, we are developing iteratively petro-physical
andgeophysical models that can explain the observables at the different scales.
In this paper, we report outthe results of the first iteration phase of this
research project that consists in building an initial petrophysical model from
well logs and prior geological knowledge, and single-domain inversion
ofgeophysical data. We applied this methodology to the Upper Rhine Graben where
a wealth ofknowledge and dataset on deep fractured formations are available.
