The revolution in seismic resolution: High density 3D spatial sampling developments and results

Abstract

Recent marine case studies have demonstrated that a significant component of the seismic "noise" contaminating 3D images actually arises during processing, as an unfortunate, and inescapable artefact from poor 3D spatial sampling. When the cross-line acquisition dimension is sampled at an equally small interval as the inline dimension, a much larger frequency bandwidth than typical of standard 3D acquisition can preserved throughout all stages of processing, free of aliasing, and free of artefacts. Hence, it is observed that once the random noise component is suppressed below a certain threshold, other factors than mere fold are clearly contributing to the quality of a seismic image. It is quite poorly established how more complicated acquisition parameters, such as multi-streamer spread dimensions and shooting templates, influence the "S/N ratio" of seismic data - particularly after the application of multichannel pre-stack processing algorithms, notably pre-stack migration.Historically, efforts at towing the source and streamer at shallower depths rather fruitlessly delivered higher dominant signal frequencies, at the cost of degraded lower frequency amplitudes, increased survey noise, and with minimal perceivable improvements in target resolution. Even if means can be found to reduce the inherent noise incurred, resolution remains frustratingly restricted, and the emphasis upon higher frequencies during acquisition was largely wasted. The solution is to sample densely in both the shot and receiver domains, particularly in the cross-line direction.Several case study examples demonstrate significant improvements in resolution and signal-to-noise content are routinely achieved by high-density seismic acquisition. Depending upon local geological conditions, high frequency amplitudes can be increased by up to 15 dB, frequency bandwidth can be doubled, 3D steep dip imaging can be significantly improved, and overall signal-to-noise ratio is improved, further contributing to better resolution. Hence, a powerful demonstration is made that tight 3D spatial sampling must be the foundation for all high resolution seismic acquisition.