PROCESSING OF A 9-COMPONENT NEAR-OFFSET VSP FOR SEISMIC ANISOTROPY

A convolutional sequence of matrix operators is offered as a convenien t deterministic scheme for processing a multicomponent vertical seismi c profile (VSP). This sequence is applied to a nine-component near-off set VSP recorded at the Conoco borehole test facility, Kay County, Okl ahoma. These data are corrected for tool spin and near-surface anisotr opy together with source coupling or imbalance. After wave-field separ ation using a standard f-k filter, each source and receiver pair for t he upgoing waves is adjusted to a common reference depth using a matri x operator based on the downgoing wavefield. The up- and downgoing wav es are then processed for anisotropy by a similarity transformation, t o separate the qS1 and qS2 waves, from which the anisotropic propertie s are estimated. These estimates reveal a strong (apparent) vertical b irefringence in the near-surface, but weak or moderate values for the majority of the subsurface. The target zone consists of a thin sandsto ne and deeper shale layer, both of which possess a strong vertical bir efringence. The sandstone corresponds to a zone of known fluid flow. A n observed qS2 attenuation and polarization change in the shale sugges t it contains large fractures.