Driving point impedance - A new paradigm for detecting fracture and in situ stress in boreholes

The mechanical properties of the rocks surrounding an orbital vibrator alter the shape and amplitude of the vibrator's orbit. Detecting these changes with driving-point impedance measurement promises to reveal fractures and possibly identify the in situ stress state and significantly increase the depth that can be investigated. The authors' research emphasis has been on detecting vertical fractures through the casing. Experimental and numerical results to date indicate that this new logging tool has excellent potential for determining both the vertical extent and azimuthal orientation of such fractures. Fracture and in situ stress orientations are useful in mine planning.