Shear-wave splitting in reflection surveys : theory, methods and case studies

• Main Author: Li, Xiangyang
• Published: University of Edinburgh 1992
• Subjects: 550
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653874

Over the last decade, the use of multi-component seismic reflection data to study shear-wave splitting has become increasingly common within the hydrocarbon industry to determine the crack geometry of oil reservoirs. Thus, it is important to investigate the characteristics of, develop processing techniques for, and carry out case studies of shear-wave splitting in reflection surveys. I have examined the effects of anisotropic symmetry, particularly orthorhombic symmetry, on velocity variations and moveouts of split shear-waves in vertical off-symmetry planes. I have also examined the effects of crack orientation changing with depth on reflection and transmission coefficients of split shear-waves. These theoretical developments in understanding shear-wave splitting in reflection surveys are described in Chapters 2 and 3. Complex component analysis was developed as an alternative to polarization analysis for displaying and identifying shear-wave splitting in large seismic datasets. This complex component analysis allows the calculation of instantaneous amplitudes and instantaneous polarizations for two-component seismic data and of shear-wave splitting sections and polarization logs for four-component data. Four field seismic datasets, including a two- and a four-component VSP, a reflection shot data matrix and a two-component crosshole survey, have been used to verify and illustrate the technique, as described in Chapters 4 and 5. A linear-transform technique was developed as an alternative to rotation analysis for quantifying and processing shear-wave splitting in seismic data. This linear-transform technique allows various attributes to be measured, including the polarizations and time delays of split shear-waves and downhole geophone orientation. It also allows time series of the split shear-waves to be separated deterministically and such separation can be made before stacking in reflection surveys. Three field datasets including a zero-offset VSP, an offset VSP and a reflection shot data matrix, have been used to verify and illustrate the technique, as described in Chapter 6.