Enhancement of prestack diffraction data and attributes using a traveltime decomposition approach

Abstract

Diffractions not only carry important information about small-scale subsurface structures, they also possess unique properties, which make them a powerful tool for seismic processing and imaging. Since a point diffractor scatters an incoming wave to all directions, a diffraction event implies better illumination than a reflection, because the rays travel through larger parts of the subsurface. Furthermore, unlike the reflection case, in which the emergence location of the reflected wave depends on the source position, in the case of non-Snell scattering, up-going and down-going raypaths are decoupled. Based on this decoupling, we introduce a diffraction traveltime decomposition principle, which establishes a direct connection between zero-offset and finite-offset diffraction wavefield attributes. By making use of this approach, we are able to enhance diffractions and obtain high-quality diffraction wavefield attributes at arbitrary offsets in the prestack domain solely based on zero-offset processing without any further optimization of attributes. We show the accuracy of the method by fitting diffraction traveltimes, and on simple waveform data. Application to complex synthetic data shows the ability of the proposed approach to enhance diffractions and provide high-quality wavefield attributes even in sparsely illuminated regions such as subsalt areas. The promising results reveal a high potential for improved prestack data enhancement and further applications such as efficient diffraction-based finite-offset tomography.K e y w o r d s :

Coherent diffraction imaging for enhanced fault and fracture network characterization

“…8, but it makes use of dynamic ray tracing to perform the subsequent projection into image space. Also, the method was shown to reliably utilize diffracted energy to arrive at a resolved estimate of scatterer locations in depth (Duveneck, 2004;Bauer et al, 2017). While the projection step, like in focusing, could be performed for a predefined velocity distribution, projection was shown to lend itself well to a largely automated reconstruction of not only the scatterer locations, but also the macro-velocity structure in an iterative process.…”

“…Likewise applied before migration, there are some techniques that make direct use of wave-field coherence for diffraction separation (Berkovitch et al, 2009;Dell and Gajewski, 2011;Bauer et al, 2016;Bakhtiari Rad et al, 2018). While these methods specifically target the diffracted wave field for extraction, recent developments have shown that a more surgical, amplitude-preserving separation can be achieved by assessing the coherence of reflections instead (Schwarz and Gajewski, 2017a;Schwarz, 2019b).…”

“…Although other methods like plane-wave destruction can achieve a similar quality of extraction in many applications, the systematic and physically intuitive assessment of coherence can be carried out in any imaginable data configuration and allows for a seamless integration of data enhancement, wave-field separation, and imaging into a single framework. Recent studies suggest that, owing to their unique properties, diffractions also lend themselves well to velocity inversion (Sava et al, 2005;Fomel et al, 2007;Decker et al, 2017;Bauer et al, 2017). These approaches bear the potential for a selfcontained imaging and inversion cycle that is also applicable in the case of offset-limited acquisitions, as they can often be found in academia (Preine et al, 2020).…”

An introduction to seismic diffraction

“…Ultimately linked to illumination, provided that the assumption of a point scatterer is reasonably justified at least for a subset of the considered wavefield, the recorded prestack diffraction response turns out to be highly symmetric and redundant (e.g. Bauer et al, 2016;Schwarz and Gajewski, 2017a).…”

Common-reflection-surface-based prestack diffraction separation and imaging

“…To illustrate the benefit of separating the full prestack diffraction response, we apply time migration velocity analysis to prestack diffraction-only data in order to obtain the required migration velocities for subsequent imaging in time. This paper only considers diffraction from point-like structures, as even more complicated diffractors such as edges or wedges, from a kinematic viewpoint, contain a non-Snell scattering component that provides increased illumination (Bauer et al, 2016(Bauer et al, , 2017. For this diffraction component, the estimated stacking velocities are intrinsically dip-independent and can readily be used for prestack or poststack time migration (see, e.g., Sava et al, 2005;Fomel et al, 2007;Berkovitch et al, 2009;Bakhtiari Rad et al, 2014).…”