Unravelling the Near Surface by Imaging Multiples and Shallow Hazard Analysis in the North Sea

Summary Conventional reflection seismic processing images primary reflectors only. When the target depth is shallower than the minimum source-to-detector distance, wide reflection angles can compromise the image. Some acquisition techniques can help overcome this limitation, but they normally incur higher costs, and many exploration programs must rely on legacy data sets. These vintages are commonly reprocessed using higher-end imaging techniques to maximize the value of the existing information. Imaging the multiples of primary reflections exploits the recorded narrower angles and the different subsurface illumination that the multiples provide. In this case study from the Alvheim field, North Sea, we demonstrate increased resolution of the shallow seismic section by imaging the source-side water-layer multiple. This delivers sharper delineation of the geological features, additional coverage, and reduction of the acquisition footprint. We also show that this product conforms with the industry standards for performing shallow hazard assessment. Imaging of the multiples provides higher confidence when modeling the shallow channels and can be used to create shallow risk maps, ultimately contributing to safe and more economical well planning.