Ultrasonic Laboratory Study of Full Waveform Acoustic Logs in Boreholes with Fractures

Abstract

A set of ultrasonic experiments was carried out to determine the effects of horizontal and vertical fractures on full waveform acoustic logs. Boreholes of 1 cm diameter were drilled in aluminum blocks. Measurements were made with horizontal fractures of 0.05 mm, 1.0 mm, 2.5 mm, and 4.5 mm width and a vertical fracture of 1.0 mm width. The horizontal fractures of even the smallest thickness significantly attenuate the P, S, and pseudo-Rayleigh waves. The Stoneley waves are the least attenuated, and attenuation increases with increasing fracture width. The vertical fracture attenuates Stoneley waves most significantly. Both scattering and fluid flow playa role in attenuation. The results may qualitatively be extended to inclined open fractures, where we expect strong attenuation of P and S waves and moderate attenuation of Stoneley waves.