Migration of multiples from the South China Sea

The South China Sea where water depth is up to 5000 m is the most promising oil and gas exploration area in China in the future. The seismic data acquired in the South China Sea contain various types of multiples that need to be removed before imaging can be developed. However, compared with the conventional reflection migration, multiples carry more information of the underground structure that helps provide better subsurface imaging. This paper presents a method to modify the conventional reverse time migration so that multiple reflections can migrate to their correct locations in the subsurface. This approach replaces the numerical impulsive source with the recorded data including primaries and multiples on the surface, and replaces the recorded primary reflection data with multiples. In the reverse time migration process, multiples recorded on the surface are extrapolated backward in time to each depth level, while primaries and multiples recorded on the surface are extrapolated forward in time to the same depth levels. By matching the difference between the primary and multiple images using an objective function, this algorithm improves the primary resultant image. Synthetic tests on Sigsbee2B show that the proposed method can obtain a greater range and better underground illumination. Images of deep water in the South China Sea are obtained using multiples and their matching with primaries. They demonstrate that multiples can make up for the reflection illumination and the migration of multiples is an important research direction in the future.