Feasibility of an acoustic technique for fracture detection

A field experiment was conducted at a granite quarry to determine the feasibility of an acoustic, downhole technique for location of fractures in the vicinity of boreholes. The frequency used in this test was about 5 kHz; a frequency well above the seismic frequency commonly used in reservoir evaluations. An existing flame-cut slot in the granite at the test site was filled with water to simulate a fracture. A high-energy piezoelectric transmitter was located in a borehole 8 meters from the water-filled slot, and a commercial piezoelectric transducer was used as a receiver in a borehole 4 meters from the slot. Both transducers could be rotated for maximum transmission or reception for either the compressional wave or the shear wave. During the experiment, reflections from the simulated fracture were obtained with the transducers oriented only for shear wave illumination and detection. These test results suggest that a high-frequency shear wave can be used to detect fractures located away from a borehole. 2 refs., 2 figs