Résumé
This thesis has been conducted on a fractured crystalline basement located in Ploemeur (South of Brittany, France). The detailed study of this basement requires a good understanding of their internal structures, namely their intrinsic properties, flow mode, density and fractures distribution. This work is focused on the petrophysical characterization of the granitic formations. Physical properties were determined from downhole geophysical measurements and images, and petrophysical measurements with thin sections made for each mini-core in the laboratory. Fresh-altered schist and fresh-altered granite separated by a normal angle fault are the main lithology of the Ploemeur crystalline basement. The results showed that the petrophysical properties were function of both porosity variation and degree of alteration and that the pore-space topology was found to be porositydependent. This thesis introduces a new formula between electrical resistivity and porosity. In addition, the laboratory measurements of Ploemeur revealed that seismic wave velocity was a function not only of porosity, but also of the predominant pore type. In general, the pore aspect ratio inverted from velocity measurements were classified roughly into crack shape. In the Ploemeur crystalline basement, the downhole geophysical measurements and images were used to measure changes in physical and chemical properties in the borehole fluid and the bedrock surrounding the boreholes. The effective integration of different geophysical methods, hydrogeological tests and lithological description was the best way to characterize the fractures in the crystalline basement, and is critical for a suitable estimation of fluid circulation.