A physical model study of effect of fracture aperture on seismic wave

Abstract

Based on Hudson’s theoretical hypothesis of equivalent fracture model, inserting aligned round chips in solid model can simulate fractured media. The effect of fractures on the propagation of P and S waves can be observed by changing the fracture thickness. The base model is made of epoxy resin, and the material of fractures is a kind of low-velocity mixture containing silicon rubber. With constant diameter and number of fractures in each model, one group of models can be formed through changing the thickness of fracture. These models have the same fracture density. By using the ultrasonic pulse transmission method, the experiment records time and waveform of P and S waves in the direction parallel and perpendicular to the fracture orientation. The result shows that, with the same fracture density, changing fracture aperture will affect both velocity and amplitude of P and S waves, and the effect on P-wave amplitude is much greater than that on the velocity. Moreover, the variation in velocity of S wave is more obvious in the slow shear wave (S2), while the variation in amplitude is more obvious in the fast shear wave (S1). These properties of wave propagation are useful for seismic data processing and interpretation.