Shear-wave VSP data processing for anisotropy

• Main Author: Zeng, Xinwu
• Published: University of Edinburgh 1994
• Subjects: 550
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664220

It has now become comparatively common in shear-wave exploration to use the measurements of the polarization direction of the leading shear-wave and the travel-time delay between this and the slow split shear-wave, to give a direct indication of the orientation and strength of anisotropy. It is important to investigate and develop suitable techniques to extract these parameters from seismic data. To investigate the anisotropic properties of shear-wave propagating in anisotropic medium, I first develop a vector convolutional model for a shear-wave propagating through an anisotropic medium in Chapter 2. Based on this unified model, four algebraic processing techniques have been developed to estimate the shear-wave polarisation and time-delay for near-offset VSPs. The techniques include both cumulative and interval techniques for either dual/multi or single sources data. These techniques are algebraic exact solutions, faster than any possible numerical equivalent, and robust to noise. Uncertainties in the ground coupling of shear sources, alignment of the source polarization, the transfer function between the geophone and the formation, and the orientation of the receiver tool in the borehole, may be amongst the principal causes of inaccuracy when estimating shear-wave splitting from multicomponent near-offset VSP data. In Chapter 3, investigations using synthetic seismograms computed for a zero-offset VSP in an anisotropic half-space, address the frequency independent part of this problem to determine how much uncertainty can be tolerated for simple amplitude and orientation variations in the source and geophone components, while still maintaining a shear-wave polarization estimated for the faster split shear-wave accurate to within 5°.