Interpreting seismic data in the presence of azimuthal anisotropy; or azimuthal anisotropy in the presence of the seismic interpretation

摘要

The earth is anisotropic, and P-wave anisotropy is often significant. Both the P-wave velocity field and amplitudes (prestack and poststack) are influenced by the anisotropy. In addition, azimuthal anisotropy is an issue in narrow-azimuth and 2D data as well as wide-azimuth 3D. The interpreter, when aware of how the anisotropy manifests itself in seismic data, can incorporate these effects into the interpretation to evaluate risk. In addition, they may be able to extend the interpretation to address the source of the anisotropy. Mostly this azimuthally varying anisotropy is attributed to fractures, which may not necessarily be macro fracturing related to reservoir permeability. Crampin has suggested that microfracturing in the earth, which may not increase reservoir permeability, is prolific. This view is supported by our observations of P-wave azimuthal velocity anisotropy over large survey areas in various parts of the continental United States. It should also be noted that any alignment, whether depositional fabric or crystallographically aligned cements filling fractures, may also cause the anisotropy. Therefore, we should not jump to the conclusion that what we observe in the anisotropy is always the open fractures.