Borehole Seismic Imaging
Borehole seismic surveys can provide valuable VTI and HTI anisotropy information, by utilizing the measured compressional and shear wavefields.
VTI anisotropy can be examined using the measured downgoing P-wave arrival times from a walkaway VSP survey, which provide vertical and horizontal slowness information for many different raypaths, which can be used to invert for Thomsen anisotropy parameters of the overburden.
HTI anisotropy information can be obtained using a multi-azimuth walkaround VSP survey, which allows the computation of horizontal velocity variation with azimuth. HTI anisotropy can also be derived using other VSP geometries if shear wave splitting is occurring, by rotating the multi-component VSP data into the radial and transverse orientation and utilizing hodograms to determine the fast and slow shear directions.