3D PP/PS Prestack Depth Migration on the Volve Field

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 clouds (Xiang-Yang Li et al., 2001) and image reflectors that are weak on PP data ( MacLeod et al., 1999), and can 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. However, imaging of PS data is reliant upon accurate compressional and shear velocity estimates, as both the moveout and offset of the imaged point depend upon these parameters. Velocity anisotropy is also a critical factor. The previously used processing flows have not adequately comprehended this, and the results have often been of poor quality and difficult to tie with the PP volumes. This can preclude their use for lithology prediction. We have implemented an imaging workflow that can resolve many of these issues, and here describe its application to OBS data from the Volve field, Norwegian Central North Sea.