Zero-offset internal multiple modeling in the image domain

In this work, we show an internal-multiple-modeling scheme acting on the postack-migrated domain. This scheme applies when prestack data is not available yet and when internal multiples are present, posing challenges to seismic interpretation. The method is computationally inexpensive, since it uses the Exploding Reflector Model and oneway propagation. We describe the theory with details of the method, and show 3D results on real data. Introduction Internal multiples interference with the Pre-salt reservoirs of the Santos Basin is a known long-standing problem. This interference is more pronounced in the presence of the socalled stratified salt, which is mainly composed by a sequence of halite interbedded with anhydrite, and can have a huge impact when determining volumetrics, since it affects facies classification, impedance inversion, as well as, sometimes, structural interpretation. In the Santos Basin, generation of internal multiples mainly occurs at the sea bottom and on the top salt. Examples of successful internal multiple attenuation in the Santos Basin include different modeling methods (Hembd et al. 2010, Cypriano et al. 2015, Krugger et al. 2018, Starring et al. 2018). Some of them are data driven, while others depend on an Earth model. Nevertheless, all of them act on the prestack data and, for this reason, are computationally intensive. Figure 1 exemplifies how misleading internal multiples can be when interfering with the Pre-salt reflectors. Steep dipping events are signal, representing periodic lava flows of the igneous basement of the Santos Basin. Gentler dip events are internal multiples. More misleading than this example is when internal multiples have dips similar to those of the Pre-salt reflectors. This can lead internal multiples to be interpreted as unconformities and even DHI’s, which can negatively affect exploratory targets. In the postack case, Filpo and Tygel (1999) used a Kirchhoff method to generate surface multiples, starting from a zero-offset stacked volume. In 2003, Pica and Manin also modeled surface multiples, but having as input a depth-migrated volume as reflectivity to generate the corresponding zero-offset stack volume via the Exploding Reflector concept. They used phase-shift extrapolation with convolution with the migrated volume to finally model the surface multiples. Wang et al. (2011) expanded Pica and Manin work to model internal multiples, using picked reflectors as the reflectivity. In this work, we propose to combine Pica and Delmas’s method with that of Wang. Our method applies not only to attenuate internal multiples in postack-migrated data, but also to validate interpretation in the presence of this noise. We describe the theory, details of the method, and show 3D results on real data from three different areas of the Santos Basin. Figure 1Steeper dip events are signal and represent periodic lava flows of the igneous basement of the Santos Basin. Gentler dip events are internal multiples.