Permeability enhancement from a hydraulic stimulation imaged with Ground
We present evidence of permeability enhancement from hydraulic
stimulation experiments in fractured crystalline rock. A total of almost
10m3 was injected in two fractured intervals of a 300 m long borehole.
Ground Penetrating Radar (GPR) measurements in the same borehole were
carried out prior to and following the stimulation. The initial
measurements revealed fractures in the vicinity of the borehole that
could be traced up to distances of 50 meters away. The data measured
post-stimulation were used in a difference-imaging approach to
illuminate changes in the GPR reflections caused by the stimulations.
The changes delineate the enhancement of a large and complex fracture
network. These changes likely correspond to changes in local aperture,
thus permeability. Our results indicate that borehole GPR yields unique
information on subtle changes in hydraulic properties within a
relatively large volume and provides a new perspective on the
characterization and monitoring of deep geothermal reservoirs.