# Overview

## Abstract

Multicomponent seismic technology has advanced to the point that the science can be practiced by anyone who wishes to take advantage of any of the applications demonstrated in the preceding chapters. It is appropriate to make a few closing remarks to reinforce that conclusion.

History shows that all seismic technologies continually evolve and advance, and multi-component technology will do so also. Because acquisition, processing, and interpretation of multicomponent data cost more than equivalent actions with single-component P-wave data, lower-cost multicomponent seismic technology is desirable. However, cost reduction will not occur quickly. Expanded use of multicomponent seismic technology probably will parallel the development of 3D seismic technology in the 1970s and 1980s. At first, the cost of 3D seismic technology was so high that the only projects that could justify acquiring 3D data were high-capital projects involving expensive drilling and construction of production facilities. After a few years, a wider community of users saw the value of 3D technology and began to request 3D seismic services at affordable prices. Once an appropriate-sized user community existed, efficiencies were introduced to lower cost, and the rest is history. Three-dimensional technology now is practiced everywhere by everyone.

Similar to the expansion of 3D seismic technology, multicomponent seismic technology probably will grow more rapidly through applications in high-capital oil and gas development projects rather than in lower-cost exploration projects. If the bottom-line cost of a project is significant, the incremental cost of using multicomponent data rather than single-component data will rarely be an issue.

Three-dimensional seismic technology became

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# Multicomponent Seismic Technology

A principle that is emphasized throughout this book is that the physics of any multicomponent seismic technology cannot be understood unless that technology is viewed in terms of the particle-displacement vectors associated with the various modes of a seismic wavefield. This material therefore begins with a discussion of seismic vector-wavefield behavior to set the stage for subsequent chapters.

Several approaches can be used to explain why each wave mode of nine-component (9C) and three-component (3C) seismic data that propagates through subsurface geology provides a different amount and type of rock/fluid information about the geology that the wave modes illuminate. Some approaches appeal to people who have limited interest in mathematics. Other options need to be structured for people who have an appreciation of the mathematics of wavefield reflectivity. Another argument that can be used focuses on the fundamental differences in P-wave and S-wave radiation patterns and the distinctions in target illuminations associated with 9C and 3C seismic sources. We will consider all of those paths of logic.

A principle that will be stressed is that each mode of a multicomponent seismic wavefield senses a different earth fabric along its propagation path because its particle-displacement vector is oriented in a different direction than are the particle-displacement vectors of its companion modes. Although estimations of earth fabric obtained from various modes of a multicomponent seismic wavefield can differ, each estimate still can be correct because each wave mode deforms a unit volume of rock in a different direction, depending on the orientation of its particle-displacement vector. Those deformations sense a different earth resistance in directions parallel to and normal to various symmetry planes in real-earth media. The logic of that nonmathematical approach appeals to people who are interested in the geologic and petrophysical information that multicomponent seismic data can provide and are less concerned about theory and mathematics.

A second approach that is helpful for distinguishing one-component (1C), 3C, and 9C wavefield behavior focuses on the mathematics of the reflectivity equation associated with each mode of the full-elastic seismic wavefield. The mathematical structure of the reflectivity equation associated with each seismic wave mode describes why and how petrophysical properties of the propagation medium affect different wave modes in different ways. The logic of that analytical approach is appreciated by scientists who are comfortable with mathematics.

All of these concepts lead to the development of a new seismic-interpretation science based on multicomponent seismic data called elastic wavefield seismic stratigraphy.