Foundations Of Anisotropy For Exploration Seismics

Over the last few years, anisotropy has become a "hot topic" in seismic exploration and seismology. It is now recognised that geological media deviate more or less from isotropy. This has consequences for acquisition, processing and interpretation of seismic data and also helps determine the cause of anisotropy and adds to our knowledge concerning the structure of the medium at scales beyond the resolution of the seismic method. This volume addresses the theoretical foundations of wave propagation in anisotropic media at an easily accessible level. The treatment is not restricted to exploration seismology. The book commences with fundamental material and covers the description of wave propagation in anisotropic conditions by means of slowness and wave surfaces. It continues to explore the theory of elasticity, the interaction of elasticity and material symmetry and conditions imposed by the stability of the medium. Wave propagation in general anisotropic solids are discussed referring in particular to singular and longitudinal directions. Slowness and wave surfaces in transversely isotropic media and in the planes of symmetry of orthorhombic media is presented and then moves on to wave propagation in orthorhombic media by means of "squared slowness surfaces". The latter part of the book deals with layer-induced anisotropy showing how a particular internal structure of a medium leads to anisotropy and how much of this structure can be recovered by "inversion" of the modelling algorithm. A few fundamental aspects of exploration seismology are also discussed. The final chapter discusses how concepts which were developed by Kelvin, but only recently understood, can be utilised to determine the symmetry class and orientation of an elastic medium.

Over the last few years, anisotropy has become a "hot topic" in seismic exploration and seismology. It is now recognised that geological media deviate more or less from isotropy. This has consequences for acquisition, processing and interpretation of seismic data and also helps determine the cause of anisotropy and adds to our knowledge concerning the structure of the medium at scales beyond the resolution of the seismic method. This volume addresses the theoretical foundations of wave propagation in anisotropic media at an easily accessible level. The treatment is not restricted to exploration seismology. The book commences with fundamental material and covers the description of wave propagation in anisotropic conditions by means of slowness and wave surfaces. It continues to explore the theory of elasticity, the interaction of elasticity and material symmetry and conditions imposed by the stability of the medium. Wave propagation in general anisotropic solids are discussed referring in particular to singular and longitudinal directions. Slowness and wave surfaces in transversely isotropic media and in the planes of symmetry of orthorhombic media is presented and then moves on to wave propagation in orthorhombic media by means of "squared slowness surfaces". The latter part of the book deals with layer-induced anisotropy showing how a particular internal structure of a medium leads to anisotropy and how much of this structure can be recovered by "inversion" of the modelling algorithm. A few fundamental aspects of exploration seismology are also discussed. The final chapter discusses how concepts which were developed by Kelvin, but only recently understood, can be utilised to determine the symmetry class and orientation of an elastic medium.

All rock masses are seismically anisotropic, but we generally ignore this in our seismic acquisition, processing, and interpretation. The anisotropy nonetheless does affect our data, in ways that limit the effectiveness with which we can use it, as long as we ignore it. This book, produced for use with the fifth SEG/EAGE Distinguished Instructor Short Course, helps us understand why this inconsistency between reality and practice has been so successful in the past and why it will be less successful in the future as we acquire better seismic data (especially including vector seismic data) and correspondingly higher expectations of it. This book helps us understand how we can modify our practice to more fully realize the potential inherent in our data through algorithms which recognize the fact of seismic anisotropy.

The purpose of this book is to give a theoretical and practical introduction to seismic-while-drilling by using the drill-bit noise. This recent technology offers important products for geophysical control of drilling. It involves aspects typical of borehole seismics and of the drilling control surveying, hitherto the sole domain of mudlogging. For aspects related to the drill-bit source performance and borehole acoustics, the book attempts to provide a connection between experts working in geophysics and in drilling. There are different ways of thinking related to basic knowledge, operational procedures and precision in the observation of the physical quantities. The goal of the book is to help "build a bridge" between geophysicists involved in seismic while drilling - who may need to familiarize themselves with methods and procedures of drilling and drilling-rock mechanics - and drillers involved in geosteering and drilling of "smart wells" - who may have to familiarize themselves with seismic signals, wave resolution and radiation. For instance, an argument of common interest for drilling and seismic while drilling studies is the monitoring of the drill-string and bit vibrations. This volume contains a large number of real examples of SWD data analysis and applications.

Takes readers on a path of discovery of rarely examined wave phenomena and their possible usage. Chapters begin by formulating a question, followed by explanations of what is exciting about it, where the mystery might lie, and what could be the potential value of answering the question.

Understanding Seismic Anisotropy in Exploration and Exploitation (second edition) by Leon Thomsen is designed to show you how to recognize the effects of anisotropy in your data and to provide you with the intuitive concepts that you will need to analyze it. Since its original publication in 2002, seismic anisotropy has become a mainstream topic in exploration geophysics. With the emergence of the shale resource play, the issues of seismic anisotropy have become central, because all shales are seismically anisotropic, whether fractured or not. With the advent of wide-azimuth surveying, it has become apparent that most rocks are azimuthally anisotropic, with P-wave velocities and P-AVO gradients varying with source-receiver azimuth. What this means is that analysis of such data with narrow-azimuth algorithms and concepts will necessarily fail to get the most out of this expensively acquired data. The issues include not only seismic wave propagation, but also seismic rock physics. Isotropic concepts including velocity, Young’s modulus, and Poisson’s ratio have no place in the discussion of anisotropic rocks, unless qualified in some directional way (e.g., vertical Young’s modulus). Likewise, fluid substitution in anisotropic rocks, using the isotropic Biot/Gassmann formula, leads to formal errors, because the bulk modulus does not appear, in a natural way, within the anisotropic P-wave velocity. This updated edition is now current as of 2014.

The material in this volume provides the basic theory necessary to understand the principles behind imaging the subsurface of the Earth using reflection and refraction seismology. For reflection seismology, the end product is a "record section" from a collection of "wiggly traces" that are recorded in the field from which information about the properties of subsurface structure and rock can be derived. For the most part, the principles of imaging are the same regardless of the depth to the target; the same mathematical background is necessary for targeting a shallow water table as for investigating the base of the earth's continental "crust" at a depth of 30-50 km.