3D PP/PS prestack depth migration on the Volve field

Abstract

Ocean-bottom seismic (OBS) methods record both compressional (PP) and converted shear-wave (PS) data. PS data have successfully been used to image through gas-obscured zones (Li et al., 2001) and to image reflectors that are weak on PP data (MacLeod et al., 1999), and can also help constrain rock property estimates (Özdemir et al., 2001). Thus, in principle, the use of PS data can significantly mitigate risk in hydrocarbon exploration and production. Unfortunately, imaging of PS data is not straightforward, due to the asymmetry of the PS raypaths (Figure 1). Accurate compressional and shear wave velocities must be derived, and the three-dimensional variability of these parameters must be comprehended by both the imaging and velocity modelling workflows. Velocity anisotropy must also be handled, if present.