Laboratory measurements of P- and S-wave anisotropy in synthetic sandstones with controlled fracture density

Abstract

We present ultrasonic laboratory measurements on synthetic sandstones containing controlled fracture density and geometry. New construction methods can provide more realistic synthetic sandstones. We build a set of sandstones containing different fracture densities and grind these rock samples into octagonal prisms with about 50mm wide faces at increments of 45° to the fracture normal. These rock samples contain different fracture densities; the fracture diameter is about 4mm and fracture thickness is about 0.06mm. P-wave and S-wave velocities in each propagation direction of these samples were measured in an ultrasonic measurement system. The laboratory results show the influence of fracture density on P-wave and S-wave velocity and anisotropy. P-wave velocity is significantly affected by the fracture density, and the velocity at 0° direction decreases sharply as the fracture density increases. Therefore P-wave anisotropy increases with the fracture density. The S-wave velocity is also influenced by the fracture density, and especially the slow shear wave velocity is more sensitive to the fracture density. The slow shear-wave velocity at 90° direction decreases sharply as the fracture density increases. More laboratory experiments will be performed on these rock samples.