Double illumination in blended acquisition

In traditional seismic surveys, interference between shot records is undesired. Therefore, the temporal interval and/or the distance between shots is chosen sufficiently large. However, in the concept of blended acquisition (also called simultaneous acquisition) the records do overlap, allowing denser source sampling and wider azimuths in an economic way. Denser source sampling and wider azimuths make that each subsurface gridpoint is illuminated from a larger number of angles and will, therefore, improve the image quality in terms of signal-to-noise ratio and spatial resolution. We show that - even with very simple blending parameters like time delays - the incident wavefield at a specific subsurface gridpoint represents a dispersed time series with a ‘complex code’. For shot record migration purposes, this time series must have a stable inverse. The illumination can be further improved by utilizing the surface-related multiples: ‘double illumination’. These multiples fill angle gaps in the illumination and/or extend the range of angles. Note that the energy contained in the multiples now contributes to the image, rather than decreasing its quality. One remarkable consequence of this property is that detector geometries play an important role in strengthening incident wavefields. We show how to quantify the contribution of the blended surface multiples to the illuminating wavefield for a blended source configuration. Results confirm that the combination of blending and multiple scattering increases the illumination quality in an economically attractive way and, therefore, will improve the quality of shot record migration results.