Full-wavefield marine survey design using all multiples

Abstract

Despite a tremendous leap in efficiency and wavefield sampling over the past two decades, it is sometimes still difficult to achieve adequate coverage and resolution with marine streamer acquisition. It is therefore necessary to carefully study the acquisition geometry, especially with respect to resolution and image quality in the crossline direction. We have extended the existing focal beam method to analyze marine streamer geometries with and without using all multiples. The focal beam analysis method provides a direct link between the acquisition parameters at the surface (number of sources, source locations, number of detectors, detector locations, and which sources are sensed by which detectors) and the image quality at a target location in the subsurface. We have further derived the concept of weighted focal beams to assess the angular aperture available for a specific acquisition configuration at the considered depth point. So far, this method has only addressed illumination by primaries. Multiples are traditionally suppressed but can instead be used in the imaging process, in which they often contribute positively by opening up the available aperture. Therefore, we have extended the focal beam analysis concept to account for multiple-reflected waves. Focal beams are more densely sampled in the ray-parameter domain when using the full wavefield (primaries and multiples). We especially addressed coverage deficiencies that can occur when the survey geometry deviates from the ideal, for example, due to feathering. As a result, extra infill lines must be acquired. We have determined how infill analysis can be performed in the depth domain via the focal beam theory. Our analysis provides the geophysical-based infill specifications to assess the impact of coverage holes on data quality. This leads to more accurate infill decisions compared with traditional common midpoint-based criteria.