Laboratory studies of ultrasonic wave response of fractures with different lengths: Anisotropy characteristics and coda analysis

Ultrasonic wave propagation in a synthetic medium with different scale fractures is investigated through the physics modeling research. The experiment model consisting of two layers, the first layer is divided into four fractured blocks with a constant fracture density but different dimension and a block without fractures as the reference region. The velocity and reflected amplitude of wave derived from the wide azimuth data processing are anisotropic due to the fractured layer. Coda wave characteristics versus offset and azimuth are obviously different for varying fracture scales. The ratio of wavelength and fracture dimension is an important parameter in the wave-fracture interaction based on the multiple scattering theory. When the wavelength of the incident wave is close to the fracture length, the scattering is dominant in the shot records and the waves are slowed and attenuated largely for the reflections from the bottoms of fractured layer and base model. The physical modeling results demonstrate that it is possible to extract fracture dimension and orientation information by analyzing code and primary waves from the reflection data. (C) 2017 Elsevier B.V. All rights reserved.