The possibility of estimating diffractor width by analyzing interfering diffraction amplitudes from end edges is examined. Although a model may be simple, it might stimulate or highlight the diffraction character of some geological features, such as small fractures, whose characterization has become an important problem in unconventional reservoirs. Results from 2D finitedifference modeling, show that analyzing interfering amplitudes on a “common distance gather” can be used in an estimation of diffractor width.
Diffractions, caused by abrupt discontinuities in subsurface elastic properties, are frequent and well-known phenomena in seismic sections. In most conventional reflection seismic programs, diffractions are treated and suppressed as coherent noise. However, the value of diffracted waves for conveying subsurface information to the surface has long been recognized. Krey (1952) was among the first authors to emphasize diffractions as signals rather than noise. Since that time, several theoretical and modeling studies have been carried out in an attempt to determine the character of diffracted waves and to extract information otherwise impossible to obtain from reflected waves. For small-scale structural and stratigraphic changes in reflectivity, such as fractures, faults, pinch-outs, and other sharp edges, most information is carried by diffracted waves (Fomel et al., 2007). Traveltime, amplitude, and phase are common wave characteristics that can be analyzed to extract this information. On an unmigrated seismic section, a diffraction traveltime curve can appear as a hyperbola whose shape is controlled by velocity and location of source, receiver, and diffractor. The diffraction curve may therefore look different in different gathers (Landa et al., 1987). Amplitude of diffraction waves, on the other hand, is controlled by frequency, distance to the diffractor, and all factors that affect reflection amplitude, such as reflection coefficient, absorption, spherical divergence, etc. (Hilterman, 1970, 1975; Trorey, 1970; Berryhill, 1977; Klem-Musatov, 1994). Most diffraction studies have focused on extracting “velocity” information, which is valuable for reflection processing or reconstructing diffractor geometry by localizing diffraction hyperbolas (Harlan et al., 1984; Landa and Keydar, 1998; Zavalishin, 2000; Khaidukov et al., 2004; Fomel et al., 2007). These studies are based mainly on information from the traveltime curve (kinematics) of the diffraction. Although the theory relating diffraction amplitudes to diffractor geometry is well known, the dynamic properties of diffractions are less acknowledged in these studies. Landa et al. (1987) proposed a method for detection and localization of diffraction that was based on both kinematic and dynamic properties of diffractions. Knasewich and Phadke (1988) also considered diffraction amplitudes in their study on imaging discontinuities in seismic sections. In this paper, the focus is on diffraction amplitude, which might provide information about the size of the diffractor. Diffraction amplitudes of diffractors of varying sizes are analyzed in a finite-difference modeling study.
According to the Huygens principle, a diffractor is a secondary source, radiating energy in all directions and appearing as a hyperbola on seismic sections. Similar to reflection amplitudes, diffraction amplitudes are affected by several factors. This approach expresses diffraction amplitudes on the basis of the reflection amplitude.
