Abstract 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.

Abstract 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

Abstract When acquiring multicomponent seismic data, careful attention must be given to the vector motions associated with P and S seismic displacements. For example, when acquiring onshore data with a vertical-displacement source, it is not necessary to be concerned about the azimuth orientation of the source at a source station. In contrast, when a horizontal-displacement source is used to generate S-wave data, it is essential to know the azimuth orientation of the source baseplate at each source station and the direction of first motion of that baseplate and to create consistent baseplate azimuth orientations at all source stations across a survey area. Likewise, it is mandatory to know the positive-polarity ends of the two horizontal sensor elements in a three-component (3C) receiver and to orient the horizontal sensors so that the positive-polarity ends point in consistent azimuths at all receiver stations. Such caution is not required when deploying vertical sensors used to acquire one-component (1C) P-wave data. If it is not possible to orient horizontal sensors in a consistent vector azimuth, as can be the case when four-component (4C) receiver nodes are deployed in deep water, a data-processing procedure must be implemented to determine sensor orientations at every receiver station. Analysis of the vector motion induced in seafloor sensors by first-arrival wavelets traveling from a large number of surface source-station coordinates is a common method used to determine 4C sensor orientation. This orientation information then can be used to mathematically transform data to a new coordinate system that describes data that would be

Abstract Multicomponent seismic data processing is a complex subject that would require a separate book to cover all aspects o the topic in a thorough manner. This chapter summarizes only basic principles and is not intended to be a complete treatise on multicomponent data-processing concepts and strategies. When nine-component (9C) data are acquired, processing S-wave data propagating in isotropic media is in concept no different than processing conventional single-component P-wave data because SH-SH and SV-SV modes satisfy the constraints of common-midpoint (CMP) data processing just as P data do. The fundamental requirement for CMP processing is that the velocity of the downgoing mode must be the same as the velocity of the upgoing mode. That assumption is valid for SH-SH and SV-SV data just as it is for P-P data. Because CMP data-processing software and expertise are widespread, processing 9C data to make SH-SH and SV-SV images is not a great challenge to a data processor skilled in processing conventional P-P data. Processing three-component (3C) and four-component (4C) data is a different matter. For those data, the velocity of the downgoing wavefield (P-wave) is not the same as the velocity of the upgoing wavefield (SV-wave), and CMP principles no longer apply. A different data-processing strategy based on common-conversion-point (CCP) principles has to be implemented. Some of the better CCP processing software is proprietary to seismic contractors and to a few research groups and service providers. The use of CCP software is beginning to be reasonably widespread, and CCP data-processing skills are expanding annually.

Abstract Rock physics is an essential part of multicomponent seismic technology. Knowledge of rock-physics principles is required to understand the behavior of P and S reflections at targeted interfaces and to explain why a P-wave image across a stratigraphic interval might look different from an S-wave image although both are correct descriptions of geologic properties that affect P- and S-wave propagation. This chapter considers two sources of rock-physics information — principles found by doing physical measurements on rock samples in a laboratory and principles developed by analyzing theoretical models of rock and fluid systems. The objective is to understand how rock and fluid properties affect P- and S-wave propagation in real rocks.

Abstract Two critical assumptions are involved in elastic wavefield stratigraphy: (1) Across some stratigraphic intervals, one mode of an elastic wavefield might show different seismic sequences and facies than its companion modes do, and (2) S-wave seismic sequences and facies are just as important in geologic interpretation as P-wave seismic sequences and facies are. Once those two assumptions are accepted, a serious interpretive challenge then is encountered — depth registration of P and S images. An interpreter must be confident that a targeted data window in P-wave image space is depth equivalent to a data window selected from S-wave image space before seismic sequences and seismic facies in the respective data windows can be combined into an elastic wavefield stratigraphy analysis. Until depth-equivalent P and S data windows are defined, no meaningful geologic interpretation of P and S sequences or facies can be done. To effectively combine P and S reflection data into a unified stratigraphic interpretation of a prospect, it is necessary to identify the specific P-wave time window and the specific S-wave time window that span each targeted stratigraphic sequence that is to be interpreted. For example, to calculate reliable V P / V S ratios over a reservoir interval, it is essential to identify P and S reflection events that define the top and base of the reservoir sequence as accurately as possible. The interpreter's dilemma is to decide which S-wave reflection event occurs at the same stratigraphic boundary where a P-wave reflection event has been interpreted. This requirement for a methodology that accurately transforms

Abstract The principles of seismic stratigraphy form the basis of modern seismic data interpretation. Seismic stratigraphy was formalized as a science by researchers at Exxon and was made available to the public through AAPG Memoir 26, published in 1977 by the American Association of Petroleum Geologists ( Payton, 1977 ). After the publication of Memoir 26, an intense period of industry education focused on the concepts and applications of seismic stratigraphy in the late 1970s and into the 1980s. Several books were published to promote the science ( Sheriff, 1980 ; Berg and Woolverton, 1985 ; Hardage, 1987 ), articles too numerous to cite were published to provide case histories, and short courses were held in many oil companies and among professional societies to implement seismic-stratigraphy practice. As a result, the interpretational principles of seismic stratigraphy became the accepted methodology for interpreting seismic images of subsurface geology in the early 1980s, and the science of seismic stratigraphy now is practiced widely and consistently. Literature searches show that the number of published papers on seismic stratigraphy is into the many hundreds, far too many citations to accumulate into a reference list. Until the mid-1990s, however, there appear to have been only five published papers that considered S-wave data in a classic seismic-stratigraphy context ( Meissner and Hegazy, 1981 ; Ensley, 1984 , 1985 ; McCormack et al., 1984 ; McCormack et al., 1985 ). More examples of S-wave seismic sequences and seismic facies are being inserted into

Abstract Because there is no viable S-wave source that can be deployed on the seafloor, multicomponent seismic data acquired in marine environments are constrained to data recorded by seafloor sensors (typically four-component [4C] sensors) and generated by air-gun arrays towed at the sea surface. Thus, SH-SH data are not available for marine applications. An SV-SV mode can be used in rare instances in which the seafloor is sufficiently hard for a downgoing P-wave to generate a robust P-to-SV mode conversion directly at the water-seafloor interface ( Tatham and Goolsbee, 1984 ). The seafloor then becomes a secondary source from which a downgoing SV mode illuminates subseafloor strata. For those reasons, only two wave modes are emphasized in marine multicomponent seismic data — the P-P mode and the P-SV mode. The applications that are illustrated in this chapter apply equally well to onshore prospects. Those examples are collected into this chapter only because the data were acquired in a marine environment, not because there is some uniqueness to marine geology or to marine seismic data. One exception to this generalization is the use of 4C data to image near-seafloor strata in deep water. This application is unique to the marine environment because there is a large elevation difference between the surface source and the seafloor receiver that allows P-P and P-SV data to be processed like walkaway vertical-seismic-profile (VSP) data. This extension of VSP data-processing principles to marine 4C data allows near-seafloor strata immediately below a receiver station to be imaged with high

Abstract Applications and examples of multicomponent seismic technology across onshore prospects are assembled in this chapter. Because dipole sources that directly contact earth strata can be used in land-based seismic fieldwork, land-based multicomponent studies involve some S-wave modes that cannot be replicated in marine environments. Specifically, the SH-SH mode is unique to onshore multicomponent applications, and for all practical purposes, so is the SV-SV mode. An SV-SV mode can exist in marine data only when a hard seafloor causes a P-to-SV mode conversion directly at the base of the water column. Even though SH sources cannot be used in offshore areas, most of the multicomponent applications that are illustrated onshore also can be implemented across marine prospects. Data examples in this chapter span several decades of investigation. Several early S-wave experiments are quite valuable for demonstrating basic principles and are included in the portfolio of rock and fluid applications assembled in this chapter so the work of first-generation proponents of S-wave technology can guide those of us who follow in their steps. The compilations of multicomponent seismic applications prepared by Stewart et al. (2003) and by Hardage (2010) are recommended reading to complement the material presented in this chapter.

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