Azimuthal Anisotropy Analysis of a Walkaround VSP: A Case Study from Saudi Arabia

Walkaround Vertical Seismic Profile (VSP) is useful for seismic azimuthal anisotropy analysis, and presents a unique opportunity to characterize the fracture distribution around a borehole. Saudi Aramco has recently completed the acquisition, processing and analysis of a walkaround VSP dataset to determine the orientation of fractures in an Ordovician sand channel in Northwestern Saudi Arabia. In this paper, the results of the azimuthal traveltime, polarization and shear-wave splitting analysis are presented and compared to fracture orientation derived from dipole sonic and image logs. The result of the azimuthal PS-wave traveltime analysis agrees very well with the dipole sonic log and indicates a NW fracture trend. The P-wave polarization analysis result shows significant scatter due to the poor data quality, but nevertheless indicates a NW fracture trend. Shear-wave splitting analyses suggest two possible fracture orientations, and one of them is consistent with the predictions from the polarization analysis results.