AVO (SEG Investigations in Geophysics No. 16) by Satinder Chopra and John Castagna begins with a brief discussion on the basics of seismic-wave propagation as it relates to AVO, followed by a discussion of the rock-physics foundation for AVO analysis including the use of Gassmann’s equations and fluid substitution. Then, the early seismic observations and how they led to the birth of AVO analysis are presented. The various approximations for the Zoeppritz equations are examined, and the assumptions and limitations of each approximation are clearly identified. A section on the factors that affect seismic amplitudes and a discussion of the processing considerations important for AVO analysis are included. A subsequent section explores the various techniques used in AVO interpretation. Finally, topics including the influence of anisotropy in AVO analysis, the use of AVO inversion, estimation of uncertainty in AVO analysis, converted-wave AVO, and the future of the AVO method are discussed. Equally helpful to new entrants into the field as well as to seasoned workers, AVO will provide readers with the most up-to-date knowledge on amplitude variation with offset.

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Observing offset-dependent seismic reflectivity has proven to be a valuable exploration tool for the direct detection of hydrocarbons. This monograph provides a comprehensive review of reflection coefficients and their approximations in isotropic media, followed by an in-depth discussion of reflection amplitudes in anisotropic media. No prior knowledge of seismic anisotropy is assumed, and considerable effort is spent to introduce wave propagation and medium parameterizations useful for surface seismic applications in the presence of anisotropy. The first anisotropic model discussed is transverse isotropy with a vertical axis of symmetry (VTI media), typically used to describe shale sequences. Then the study of VTI reflection coefficients is extended to transverse isotropy with a horizontal axis of symmetry (HTI) - the symmetry system that describes a system of parallel vertical cracks. Analysis of the "Shuey-type" approximate HTI P-wave reflection coefficient makes it possible to devise fracture-detection algorithms based on the inversion of azimuthal differences of the P-wave AVO gradient. The monograph also presents analysis of shear- and converted-wave reflection coefficients for HTI and orthorhombic models, discusses practical aspects of applying the azimuthal AVO analysis, and mentions promising recent results.

The ultimate aim of the oil exploration industry is to determine the distribution of rock types and underground fluids. At this stage, we can actually determine the distribution of several underground physical properties with a certain accuracy. The challenge for the rock physicist is to translate those physical properties (P-velocity, S-velocity, density) into rock types and fluids (gas-, or oil-, or water-bearing sand, shale). If performed correctly, dry holes can be avoided and millions of dollars can be saved. Ultimately, an integrated approach is required. This book deals with a series of topics in rock physics, including elasticity, pore pressure, incompressibility of rocks and the Gassmann equation, fluid substitution, forward modelling and empirical equations, rock physics applications to AVO studies and inversion studies, and the Differential Effective Medium (DEM) method. It is generally addressed to the practitioner (geophysicist, geologist), and in some instances, detailed instructions are furnished to perform a particular task. Some chapters, on the other hand, are theoretical and more mathematical, and are expected to be of interest to both practitioners and students alike. Other chapters include innovative ideas that could, for instance, be tested by oil companies that have substantial amounts of data at their disposal. This book will serve as a useful guide to practitioners (geologists, petrophysicists, geophysicists and reservoir engineers) and students/academics.

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