Wave-equation angle-based illumination weighting for optimized subsalt images

Abstract

A methodology has been developed for improving seismic depth images generated in areas of complex structure, such as subsalt. The main goal of the wave-equation angle-based illumination workflow is to calculate a set of illumination weight gathers and apply them to migrated field angle gathers. To obtain meaningful illumination weight gathers, it is important to use the field-acquisition geometry information, migration velocity models, and interpreted horizons. The workflow is model based and requires horizons conformable to real structure, preferably picked on the field seismic depth images. The workflow is implemented using one-way and two-way wave-equation methods and is tested on narrow-azimuth towed-streamer (NATS) and merged NATS with wide-azimuth towed-streamer (XWATS) data sets. The method weights down poorly illuminated areas while preserving strongly illuminated areas, which is opposite to the compensation methods. As a result, an overall improvement in seismic depth images can be observed, especially in subsalt areas. The impact of the workflow on improving well-tie estimation at the Thunder Horse subsalt development in the Gulf of Mexico is demonstrated.