Ultrasonic Measurements of Seismic Anisotropy in Synthetic Silica Cemented Sandstones with Controlled Fracture Geometry

摘要

We present ultrasonic measurements on two sets of novel synthetic, porous, silica cemented sandstone samples with a controlled fracture geometry. X-Ray CT scanning was used to determine the fracture density of each sample.Asmaller block was cored and measured in the ultrasonic pulse-echo system and the results revealed that shear-wave splitting was 100 times fracture density and independent of pore fluid viscosity for wave propagation at 90° to the fracture normal.Alarger block was ground into an octagonal shape and measured at ambient pressures using a bench-top method. We collected P- and S-wave velocity and attenuation data for five angles relative to the fracture normal. These measurements showed evidence for fluid-dependent shear-wave splitting at 45° to the fracture normal associated with changes in fluid viscosity.