Feasibility of an Acoustic Technique for Fracture Detection

Abstract

A field experiment was conducted at a granite quarry to determine the feasibility of an acoustic, downhole technique for location 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 field with water to simulate a fracture. A high energy piezoelectric transmitter was located in a borehole 8 meters form the water filled slot, and a commercial piezoelectric transducer was used a receiver in a borehole 4 meters form the slot. Both transducers could be rotated for maximum transmission or reception for either the compression 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.