Step Change in Shallow Water Reflection Seismic by Advances in De-Multiple Techniques

A high-resolution survey with a total of 2300 km2 of 3D reflection seismic data was acquired over the Al Shaheen Field, Block 5, offshore Qatar, from October 2006 to April 2007. Reverberations from the hard shallow water bottom and other types of noise limited the value of the original processing. Re-processing using new technologies has produced a step change in quality resulting in cleaner images for interpretation and superior angle stacks for inversion. The multiples were removed by applying an enhanced processing workflow based on a predictive, data-driven algorithm. The workflow involved attenuating short-period water-layer related multiples – a process that is referred to as shallow water demultiple (SWD). The SWD method makes use of water-layer multiples in the data to reconstruct the missing water-bottom primary reflection, and then uses the reflection for predicting these shallow multiples. The method takes into account the spatial varying nature of the subsurface. Since the multiple model predicted by SWD has similar amplitude and phase as the input data, very short matching filters can be utilised in the adaptive subtraction process. These processing improvements have influenced a broad spectrum of interpretations such as better structural representation including fault mapping and improved understanding of facies. In conclusion, detailed and careful testing has resulted in new added value from this large high resolution 3D data set by applying technologies that were not available when the data was acquired and processed in 2006-2008.