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Seismic waves can either be reflected or diffracted by subsurface objects depending on the object's geometry. Diffactions can be used to determine details about the small-scale features that generate them, such as karsts, voids, pinchouts, faults, fractures, and salt flanks. Diffraction imaging can have resolution below the typical seismic wavelength. Scattered waves are recorded as significantly lower-energy signal than reflected waves, requiring that diffractions be separated from reflections. I describe three methods of such separation: data-domain plane-wave destruction, Fresnel zone Elimination, and partial-image plane-wave destruction. Once separated, diffractions can be migrated to create a seismic diffraction image and used in velocity analysis. Common-reflection angle migrated diffractions appear flat in dip angle gathers when migrated with correct velocity. I illustrate how this property can be used to determine migration velocity through a process of oriented velocity continuation (OVC). In OVC framework diffraction data are decomposed by slope and migrated over a range of velocities. Velocities corresponding to the flattest slope gathers are picked using semblance as a measure of flatness. This provides an estimate of migration velocity. Stacking gathers corresponding to this chosen velocity generates a seismic diffraction image. Seismic diffraction images provide interpreters with information about small-scale geologic objects that may not be available in conventional images. Scattering features that are interesting for exploration, like voids, caves, fractures, and faults, cause diffractions and can be resolved with better focus in diffraction images than in conventional ones. This is particularly useful with geologically complex carbonate systems. Carbonates are strongly heterogeneous, making them difficult to image with conventional methods. Reservoir porosity is often contained within caves, or small vugs. These features are difficult to characterize with conventional methods because cave reflections have large geometric uncertainties in cave size and location. Velocity analysis of seismic reflection data in carbonates may not highlight vugular porosity particularity well. I illustrate how diffraction images provide improved characterization by highlighting the edges of caves, thus constraining cave geometry, and highlighting more heterogenous zones by measuring the amount of scattering those zones generate.
Seismic Imaging Methods and Application for Oil and Gas Exploration connects the legacy of field data processing and imaging with new research methods using diffractions and anisotropy in the field of geophysics. Topics covered include seismic data acquisition, seismic data processing, seismic wave modeling, high-resolution imaging, and anisotropic modeling and imaging. This book is a necessary resource for geophysicist working in the oil and gas and mineral exploration industries, as well as for students and academics in exploration geophysics. Provides detailed methods that are used in the industry, including advice on which methods to use in specific situations Compares classical methods with the latest technologies to improve practice and application in the real world Includes case studies for further explanation of methods described in the book
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.
Providing a broad and intuitive understanding of seismic-imaging concepts and methods to enable geoscientists to make appropriate decisions during acquisition, processing, imaging, and interpretation, this book shows trends in imaging research and encourages the adoption of new technologies to facilitate the optimal use of these images.
Covering ideas and methods while concentrating on fundamentals, this book includes wave motion; digital imaging; digital filtering; visualization aspects of the seismic reflection method; sampling theory; the frequency spectrum; synthetic seismograms; wavelet processing; deconvolution; seismic attributes; phase rotation; and seismic attenuation.
This book describes the theory and practice of inverting seismic data for the subsurface rock properties of the earth. The primary application is for inverting reflection and/or transmission data from engineering or exploration surveys, but the methods described also can be used for earthquake studies. Seismic Inversion will be of benefit to scientists and advanced students in engineering, earth sciences, and physics. It is desirable that the reader has some familiarity with certain aspects of numerical computation, such as finite-difference solutions to partial differential equations, numerical linear algebra, and the basic physics of wave propagation. For those not familiar with the terminology and methods of seismic exploration, a brief introduction is provided. To truly understand the nuances of seismic inversion, we have to actively practice what we preach (or teach). Therefore, computational labs are provided for most of the chapters, and some field data labs are given as well.
Providing geophysicists with an in-depth understanding of the theoretical and applied background for the seismic diffraction method, “Classical and Modern Diffraction Theory” covers the history and foundations of the classical theory and the key elements of the modern diffraction theory. Chapters include an overview and a historical review of classical theory, a summary of the experimental results illustrating this theory, and key principles of the modern theory of diffraction; the early cornerstones of classical diffraction theory, starting from its inception in the 17th century and an extensive introduction to reprinted works of Grimaldi, Huygens, and Young; details of the classical theory of diffractions as developed in the 19th century and reprinted works of Fresnel, Green, Helmholtz, Kirchhoff, and Rayleigh; and the cornerstones of the modern theory including Keller’s geometrical theory of diffraction, boundary-layer theory, and super-resolution. Appendices on the Cornu spiral and Babinet’s principle are also included.
One of the problems encountered in a variety of near-surface investigations is detecting and mapping localized inhomogeneities. Typical examples of such inhomogeneous sources are cavities, caves and tunnels. Different methods for detecting shallow subsurface sources utilizing seismic waves diffracted by these sources were proposed by many researchers in the last three decades. Most of these methods suggest that every subsurface point is a possible location of a point diffractor. Imaging of the diffractors is based on a spatial summation of the diffracted wavefield along diffraction time surfaces (defined by source-receiver geometry) in 2D or 3D space. The summation is performed with a fixed velocity value estimated from velocity analysis of the diffraction data. In this study, we present a path integral summation approach, where for every subsurface point the wavefield is stacked together along all possible diffraction time surfaces having a common apex at a given time. The result of the imaging is a 3D volume in which prominent diffraction anomalies appear at spatial locations close to the imaged sources. This path integral summation approach has been successfully tested on synthetic data and further applied at several sites with known subsurface sources.
This tutorial serves as a practical guide on seismic tomography for an audience familiar with basic seismology concepts and calculus. The intent is to provide the reader with a fundamental understanding of both seismic-ray tomography and seismic-diffraction tomography. Case studies illustrate processing methodology, basic interpretation techniques, and pitfalls. This presentation assists the reader in gaining a greater understanding of and appreciation for seismic-tomography articles found in the literature.