Present status and future directions of shear-wave seismology in exploration
Robert H. Tatham, Robert R. Stewart
Shear-waves respond to a different combination of elastic constants, and density, than P-waves. The reflected P-wave however, is often the easier wave-type to generate, record, and process routinely, and has become the standard for imaging of subsurface structure. Including shear-wave data into our interpretations has led to discrimination of gas-related from non-hydrocarbon related reflection amplitude anomalies. Furthermore, combining time measurements of P- and S-wave data has led to estimation of lithology in the subsurface and estimation of fracture parameters from multicomponent VSP data. Recognition of the need to apply rotational corrections for the azimuthal anisotropy that pervades in many areas has led to consistent three-component recording. More recent developments have improved our capability to record and successfully process mode-converted data, particularly P-SV reflected data. Improvements in processing, including proper 'binning' and DMO correction of the asymmetric geometry associated with the P-SV reflection path is becoming routine. As new developments evolve, high-quality structural P-SV sections, simultaneous inversion of P-P and P-SV data for variations in P- and S-wave velocity, interpretation of P-P and P-SV reflection sections for Vp/Vs ratios in stratigraphic intervals, and inclusion of P-P and P-SV AVO analysis could lead to a fully integrated interpretation of structure, lithology, porosity and reduction in the risk of finding hydrocarbons.