Multiscattering illumination in blended acquisition

Abstract

In traditional seismic surveys, the firing time between shots is such that the shot records do not interfere in time. However, in the concept of blended acquisition, the records do overlap, allowing denser source sampling and wider azimuths in an economic way. A denser shot 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. In a next step, we show that the illumination can be further improved by utilizing the surface-related multiples. This means that these multiples can be exploited to improve the incident wavefield by filling angle gaps in the illumination and/or by extending the range of angles. In this way, the energy contained in the multiples now contributes to the image, rather than decreasing its quality. One remarkable consequence of this property is that the benefits to be obtained from the improved illumination depend on the detector locations in acquisition geometries as well. 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 energy and, therefore, will improve the quality of shot-record migration results beyond today’s capability.