ABSTRACT
For a relatively shallow experiment (between 400 and 800 m) both borehole observations and induced seismicity locations indicate that flow occurred in pre-existing fractures inclined with respect to the principal stress direction. For a deep (between 2800 and 3700 m) reconnaissance programme (about 40000 m3 injected water), two situations have been observed. When the injection pressure remains lower than the minimum principal stress, flow occurs along pre-existing fractures inclined at about 30 ° to the maximum principal stress direction. When the injection pressure is slightly larger than the minimum principal stress, the water leaves the well along pre-existing weakness planes, but the mean flow direction is parallel to that of the maximum principal stress.
