Physical and numerical model study of diffraction effects on seismic profiles over simple structures
D. R. Pant, S. A. Greenhalgh, B. Zhou, 2016. "Physical and numerical model study of diffraction effects on seismic profiles over simple structures", Seismic Diffraction, Kamil Klem-Musatov, Henning Hoeber, Michael Pelissier, Tijmen Jan Moser
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2-D scale models and synthetic seismograms have been used to study diffraction artifacts and interpretation pitfalls on seismic profiles over two classes of simple-shaped structures: a vertical fault model and a rectangular mound model.
The fault throw was varied from one eighth of a wavelength (A/8) to two wavelengths (2A). For throws greater than A/2, the structure is resolved in the x-t domain but diffractions which are present convey misleading structure. Amplitude and wavelet anomalies are observed for small fault displacement (<A/2) which serve to detect but not to define the exact fault position and extent. Migration improves but does not necessarily overcome the problem.
Mound structures having heights of A/8 to 2A, and length of one half to twice the Fresnel zone radius, were investigated. Lateral resolution is improved as the length of the structure increases, but only for mounds which are vertically resolved (height greater than A/2). For low relief mounds, resolution deteriorates with increasing mound length. The resulting edge diffractions, which interfere with the reflection events, serve to detect and identify the target. Amplitude anomalies are observed across the structures, but it is not possible (without calibration) to interpret the edges of the model. Even for thick mounds the diffraction patterns complicate the seismic picture and can lead to false interpretation.
The migration aperture needs to be about 10 times the Fresnel zone radius to produce satisfactory results. However, for vertically unresolved structures, migration may not significantly help. Complicating factors with post-stack migration are lack of knowledge of the true velocity function and inadequacy of the CMP zero-offset equivalence assumption.
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The use of diffraction imaging to complement the seismic reflection method is rapidly gaining momentum in the oil and gas industry. As the industry moves toward exploiting smaller and more complex conventional reservoirs and extensive new unconventional resource plays, the application of the seismic diffraction method to image sub-wavelength features such as small-scale faults, fractures and stratigraphic pinchouts is expected to increase dramatically over the next few years. “Seismic Diffraction” covers seismic diffraction theory, modeling, observation, and imaging. Papers and discussion include an overview of seismic diffractions, including classic papers which introduced the potential of diffraction phenomena in seismic processing; papers on the forward modeling of seismic diffractions, with an emphasis on the theoretical principles; papers which describe techniques for diffraction mathematical modeling as well as laboratory experiments for the physical modeling of diffractions; key papers dealing with the observation of seismic diffractions, in near-surface-, reservoir-, as well as crustal studies; and key papers on diffraction imaging.