Offset Vector Tile Anisotropic Tomography and PreSDM of the Hild OBC

Abstract

In this work, we have performed model building and 3D PreSDM on P-wave data from a 3D OBC survey using offset vector tile (OVT) processing, wherein the velocity is estimated by a surface fitting non-sectored approach, characterising velocity in terms of a fast and slow direction, along with the azimuth of the fast axis. Using OVT VTI tomographic inversion permits us to thereby better resolve localized heterogeneity that is usually left unresolved when using a conventional non-OVT tomographic approach. In addition to the OVT VTI tomography, we followed the 3D PreSDM model building and migration with an HTI azimuthal velocity analysis in an attempt to characterize any dominant fracture patters: in this case, no dominant patterns were f ound. We compare the results with existing data showing how rigorous handling of azimuths better constrains the lateral velocity variations and results in a better focused image in the Jurassic, especially of steep fault planes.

Multi-azimuth Anisotropic Tomography and PreSDM of a North Sea Streamer Survey

“…In conventional 3D seismic data processing, we typically sort the data in a number of 3D commonoffset volumes, each offset volume comprising a limited range of offsets, but in doing so, we bin across any variation in azimuth that may exist in the recorded data (Williams and Jenner 2001). Ideally, it would be best not to bin across azimuth at all, and to work with fully sampled offset vector tile (OVT) data, as was demonstrated for OBC data over this field last year (Valler et al, 2012). One of several compromise solutions to full azimuth-offset sampling is the multi-azimuth (MAZ) acquisition approach, where we collect a set of mono-azimuth surveys, each shot with a different orientation, and proceed to process each of these data sets in tandem, leading up to a MAZ velocity model building tomographic solution.…”