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

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. A smaller 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. A larger 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.