Orthorhombic full-waveform inversion for imaging the Luda field using wide-azimuth ocean-bottom-cable data

摘要

Ocean-bottom-cable (OBC) acquisition has become the new trend in the Bohai Bay area as a result of the operational flexibility, better illumination, better multiple elimination, and better signal-to-noise (S/N) ratio it brings for targets at middle-to-deep depths. However, the presence of azimuthal anisotropy poses severe challenges to imaging with wide-azimuth (WAZ) OBC data, in particular when imaging fault planes, which are very sensitive to velocity errors. The fault images can be smeared and fault shadows observed within complex strike-slip fault systems if the azimuthal dependency of wave propagation is not properly modeled and velocity variations across faults are not properly resolved. To address these kinds of imaging challenges in the Luda field WAZ OBC data, we have developed a practical orthorhombic full-waveform inversion (FWI) approach to reconstruct high-resolution models in the presence of azimuthal anisotropy. We demonstrate that our orthorhombic FWI approach can produce a high-resolution velocity model that reconciles the structural discrepancies between seismic images from different azimuths and significantly improves the focusing of the fault planes and the quality of the image beneath the faulting system. The combined effect of these improvements gives a clear uplift in the final seismic image.