Compression waves reflection from the low-velocity azimuthally anisotropic medium: A physical model study

Interest in azimuthal anisotropy of rocks is mainly associated with fractured reservoirs, which may contain hydrocarbon deposits. Cracks in such deposits in most cases have a subvertical orientation, which is caused by the predominance of vertical stresses in rocks over horizontal ones. To determine the azimuthal direction of fractures, one can use, in particular, the dependence of the reflection coefficients of elastic waves on the boundaries with such media on the azimuth. This paper presents the results of physical modelling, demonstrating this dependence. To conduct experiments, we developed a technology for manufacturing models of azimuthally anisotropic (HTI) media with a high degree of anisotropy by 3-D printing. The features of the reflection of compression waves from the boundary of water and low-velocity azimuthally anisotropic media were experimentally investigated on the example of the model HTI medium produced by this method. Experiments have shown that at angles of incidence less than 25°, the reflection coefficients are practically independent from the azimuth. However, at larger angles of incidence, an azimuthal dependence of the reflection coefficients is observed, most pronounced at azimuths from 45° to 75°. The results of measurements in the direction of the isotropy plane agree well with the theoretical reflection coefficients for the boundary of isotropic media.