| Popis: |
Summary Fractures usually spread over various scales and have a strong influence on rock properties. We investigate seismic velocity and anisotropy in fractured media with different fracture sizes. Using synthetic rocks with controlled fracture geometries, we create a set of rocks with fracture sizes 2mm, 3mm and 4mm, and fracture densities 4.8%, 4.86% and 4.8% respectively. Fracture thickness is 0.06mm. P and S wave velocities are measured at 0.5 MHz while the rock samples are saturated by water. The laboratory observations proved that rocks containing different scale fractures can show different strengths of seismic anisotropy even with the same fracture density. While a few large fractures and many small fractures can have the same fracture density, small scale fractures cause a lower seismic wave velocity compared with large fractures. The theoretical predictions on shear wave anisotropy, as well as the P wave anisotropy in air saturation, are not affected by fracture size. In contrary, the measured results show anisotropy are apparently affected by the various size fractures. |
