Diffraction imaging in depth

Abstract

A B S T R A C THigh resolution imaging is of great value to an interpreter, for instance to enable identification of small scale faults, and to locate formation pinch-out positions. Standard approaches to obtain high-resolution information, such as coherency analysis and structure-oriented filters, derive attributes from stacked, migrated images. Since they are image-driven, these techniques are sensitive to artifacts due to an inadequate migration velocity; in fact the attribute derivation is not based on the physics of wave propagation. Diffracted waves on the other hand have been recognized as physically reliable carriers of high-or even super-resolution structural information. However, high-resolution information, encoded in diffractions, is generally lost during the conventional processing sequence, indeed migration kernels in current migration algorithms are biased against diffractions. We propose here methods for a diffractionbased, data-oriented approach to image resolution. We also demonstrate the different behaviour of diffractions compared to specular reflections and how this can be leveraged to assess characteristics of subsurface features. In this way a rough surface such as a fault plane or unconformity may be distinguishable on a diffraction image and not on a traditional reflection image.We outline some characteristic properties of diffractions and diffraction imaging, and present two novel approaches to diffraction imaging in the depth domain. The first technique is based on reflection focusing in the depth domain and subsequent filtering of reflections from prestack data. The second technique modifies the migration kernel and consists of a reverse application of stationary-phase migration to suppress contributions from specular reflections to the diffraction image. Both techniques are proposed as a complement to conventional full-wave pre-stack depth migration, and both assume the existence of an accurate migration velocity.

Poststack diffraction imaging using reverse-time migration

“…However, zero-offset stacking requires an accurate velocity analysis and special stacking procedures to preserve diffracted events. Moser and Howard (2008) showed that the conventional normal moveout stack may remove information about diffractions due to the different moveouts between diffracted and reflected waves. One possibility for obtaining a zero-offset approximation while preserving the diffracted energy is to use the path summation technique, which optimally stacks coherent events with all possible stacking velocities (Landa et al 2006).…”

High-resolution imaging of diffractions — A window-steered MUSIC approach

“…Similarly, Fomel et al (2007) use plane-wave-destruction filters to perform diffraction separation. From an imaging point of view, Moser and Howard (2008) use antistationary filtering to separate reflective and diffractive components during the migration, while Zhang (2004) performs prestack depth diffraction imaging using the idea of the Fresnel aperture. Diffraction enhancement can also be carried out using MF (Berkovitch et al, 2009) or the CRS (e.g., Asgedom et al, 2011b;Dell and Gajewski, 2011) stacking methods.…”

“…More recently, much attention has been paid to the enhancement and separation of diffractions from reflection data for many imaging purposes. Several approaches have been proposed, among them the use of antistationary filtering (Moser and Howard, 2008), plane-wave destruction filters (Fomel et al, 2007), multifocusing (MF) (Berkovitch et al, 2009), or the common reflection surface (CRS) (Asgedom et al, 2011a(Asgedom et al, , 2011b(Asgedom et al, , 2012a(Asgedom et al, , 2012b stacking methods. Because the diffracted events are known to carry high-resolution information about the subsurface, their optimal use in imaging is an important topic.…”

Diffraction imaging in fractured carbonates and unconventional shales

“…The importance of diffractions in high-resolution structural imaging has been emphasized in many recent publications (Khaidukov et al, 2004;Kozlov et al, 2004;Fomel et al, 2006;Landa et al, 2008;Moser and Howard, 2008;Moser, 2009;Klokov et al, 2010;Dell and Gajewski, 2011;Koren and Ravve, 2011;Klokov and Fomel, 2012;Decker et al, 2013;Popovici et al, 2014;Sturzu et al, 2014), and diffraction imaging is emerging as a new tool in seismic interpretation. By careful preprocessing, the inherent redundancy of prestack seismic data can be used to separate the contribution of high-energy specular events from those of low-amplitude events scattered by local unconformities and heterogeneities.…”