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`NUMBER 7
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`'* II
`I
`A t
`A Handbook for
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`Seismic Data Acquisition
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`in Exploration
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`r
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`!
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`HiBy Brian J. Evans
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`A
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`society of exploration geopliysicists
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`GEOPHYSICAL MONOGRAPH SERIES
`
`David V. Fitterman, Series Editor
`
`William H. Dragoset ]r., Volume Editor
`
`NUMBER 7
`
`A HANDBOOK FOR SEISMIC DATA
`
`ACQUISITION IN EXPLORATION
`
`By Brian]. Evans
`
`SOCIETY OF EXPLORATION GEOPHYSICISTS
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`WesternGeco V. PGS (IPR2015-00309, 310, 311)
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`Evans, Brian J., 1945 -
`A handbook for seismic data acquisition in exploration / by Brian J. Evans;
`edited by William H. Dragoset, Jr.,
`p.
`cm. — (Geophysical monograph series : no. 7)
`Includes bibliographical references and index.
`ISBN 1-56080-O41-0 (paper : alk. paper)
`1. Seismic prospecting.
`l. Dragoset, William H.
`TN269.8.E93 1997
`622'.1592——dc20
`
`II. Title.
`
`III. Series.
`
`96—42041
`ClP
`
`ISBN 978—0—93l830~56-3 (Series)
`ISBN 978—1—56080—041-5 (Volume)
`
`Society of Exploration Geophysicists
`P. O. Box 702740
`Tulsa, OK 74170-2740
`
`© 1997 by Society of Exploration Geophysicists
`All rights reserved. This book or parts hereof may not be reproduced in any form
`without written permission from the publisher.
`
`Published 1997
`Reprinted 1997, 2005, 2007, 2009
`Printed in the United States of America
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`

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`To my wife, Margaret, who not only typed for endless
`weekends to complete the earlier versions of this text but
`who waited at home for many months in anticipation of
`my returning from the field. The good thing about going
`away is coming home again.
`
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`Contents
`
`Preface .............................................................................................. .. xi
`
`1
`
`Seismic Exploration ................................................................. ..1
`1.1
`Introduction ...................................................................... ..1
`
`1.2 Seismic Data Acquisition ................................................ ..2
`1.2.1 Historical Perspective .......................................... ..2
`1.2.2 Modern Data Acquisition .................................... ..5
`1.3 Seismic Wave Fundamentals ........................................ ..12
`
`1.3.1 Types of Elastic Waves ...................................... ..13
`1.4 The Common Midpoint Method .................................. ..28
`1.4.1 Source / Receiver Configuration and Fold ...... ..31
`1.4.2 Stacking Diagrams ............................................. ..34
`1.5 Survey Design and Planning ........................................ ..38
`1.5.1 Seismic Resolution ............................................. ..39
`
`1.5.2 Survey Costs and Timing .................................. ..40
`1.5.3 Technical Considerations .................................. ..42
`
`1.5.4 Special Considerations ...................................... ..44
`Exercise 1.1 ............................................................................... ..45
`
`Exercise 1.2 ............................................................................... ..46
`
`2
`
`Receiver Design and Characteristics ................................. ..47
`2.1 Land Receiver Systems (Geophones and Cables) ...... ..48
`2.1.1 Frequency Response and Damping ................. ..49
`2.1.2 Electrical Characteristics ................................... ..52
`
`2.1.3 Physical Characteristics ..................................... ..52
`2.1.4 Special Geophones ............................................. ..55
`2.1.5 Geophone Response Testing ............................ ..59
`2.1.6 Cables ................................................................... ..61
`
`2.2 Marine Receiver Systems (Hydrophones and
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`Streamers) ........................................................................ ..64
`2.2.1 Hydrophones ...................................................... ..64
`2.2.2 Streamers ............................................................. ..67
`
`2.2.3 Depth Control ..................................................... ..69
`2.2.4 Streamer Depth Indicators ................................ ..71
`2.2.5 Streamer Heading .............................................. ..71
`2.2.6 Streamer Noise ................................................... ..71
`
`2.3 Fundamentals of Array Design .................................... ..73
`2.3.1 Synthetic Record Analysis ................................ ..75
`2.3.2 Receiver Array Design....................................... ..77
`2.4 Symmetric and Asymmetric Recording ...................... ..93
`2.5 Receiver Ghosting .......................................................... ..94
`Exercise 2.1 ............................................................................... ..95
`
`Exercise 2.2 ............................................................................... ..95
`
`Exercise 2.3 ............................................................................... ..95
`
`Exercise 2.4 ............................................................................... ..97
`
`Seismic Energy Sources ........................................................ ..99
`3.1 Source Array Design .................................................... ..101
`3.2 Land energy sources ................................................... ..103
`3.2.1 Land Explosives ............................................... ..104
`3.2.2 Vibroseis ............................................................ ..11O
`
`3.2.3 Other Land Energy Sources ............................ ..126
`3.3 Marine Energy Sources ................................................ ..132
`3.3.1 Air Guns ............................................................ ..134
`3.3.2 Sparker ............................................................... ..136
`3.3.3 Flexotir ............................................................... ..136
`
`3.3.4 Maxipulse .......................................................... ..137
`3.3.5 Detonating Cord ............................................... ..137
`3.3.6 Gas Gun ............................................................. ..137
`
`3.3.7 Water Gun ......................................................... ..138
`
`3.3.8 Steam Gun ......................................................... ..139
`
`3.3.9 Flexichoc ............................................................ ..141
`
`3.3.10 Vibroseis ............................................................ ..141
`
`3.4 Marine Air-Gun Arrays ............................................... ..141
`3.4.1
`Far—Field Testing ............................................... ..145
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`3.4.2 Shot Timing ....................................................... ..147
`3.4.3 Relative Energy Source Levels ....................... ..148
`3.5 Source and Receiver Depth (Ghost Effect) ............... ..149
`3.6 Determining Optimum Air—Gun Specifications ...... ..155
`Exercise 3.1 ............................................................................. ..155
`Exercise 3.2 ............................................................................. ..156
`Exercise 3.3 ............................................................................. ..156
`Exercise 3.4............................................................................. ..157
`
`Seismic Instrumentation .................................................... ..159
`4.1
`Introduction .................................................................. ..159
`4.2 Basic Concepts .............................................................. ..160
`4.2.1 Basic Components ............................................ ..161
`4.2.2
`Instrument Noise and Sampling .................... ..163
`4.3 Filtering .......................................................................... ..165
`4.4 Amplification ................................................................ ..171
`4.5 A / D Conversion ........................................................... ..172
`4.5.1 Converter Operation ........................................ ..174
`4.6 Dynamic Range ............................................................ ..175
`4.7 Recording ...................................................................... ..176
`4.7.1 Formats .............................................................. ..176
`4.7.2 Recording Channels ......................................... ..179
`4.8 Miscellaneous................................................................ ..180
`4.8.1 Telemetry ........................................................... ..180
`4.8.2 Sign-Bit Recording ........................................... ..181
`4.8.3 Field Computers ............................................... ..183
`Exercise 4.1 ............................................................................. ..184
`
`Survey Positioning .............................................................. ..187
`5.1
`Introduction .................................................................. ..187
`5.2 Maps and Projections ................................................... ..189
`5.3 Geodetic Datuming ...................................................... ..192
`5.4 Land Surveying ............................................................ ..195
`5.5 Satellite Surveying ....................................................... ..198
`5.5.1 Global Positioning System (GPS) ................... ..200
`5.6 Radio Navigation ......................................................... ..201
`
`4
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`5.6.1 Phase Comparison ........................................... ..204
`5.6.2 Range Measurement ........................................ ..206
`5.6.3 Other Radio Navigation Systems ................... ..209
`5.7 Navigation Systems ..................................................... ..211
`5.8 Navigation Planning for an Offshore Program
`Using Radio Positioning Systems .............................. ..214
`5.8.1 Distance ............................................................. ..214
`
`5.8.2 Accuracy ............................................................ ..214
`5.8.3 Timing ................................................................ ..215
`5.8.4 Cost ..................................................................... ..215
`
`5.8.5 Number of Vessels ........................................... ..215
`
`Exercise 5.1 ............................................................................. ..216
`
`Exercise 5.2 ............................................................................. ..217
`
`Establishing Field Parameters ........................................... ..221
`6.1 Survey Planning ........................................................... ..221
`6.2 Noise Analysis .............................................................. ..222
`6.2.1 Spread Types ..................................................... ..223
`6.3 Experiments for Designing Parameters .................... ..226
`6.3.1 Array Performance Analysis Using 2-D
`Frequency Transforms .................................. ..227
`6.3.2 Crude f—k Plotting ............................................. ..228
`6.4 Dip Recording and Beaming Effect ........................... ..230
`6.5 Parameter Optimizing ................................................. ..231
`6.5.1 Receiver Frequency .......................................... ..231
`6.5.2 Energy Source Parameters .............................. ..232
`Exercise 6.1 ............................................................................. ..241
`
`Three-Dimensional Surveying ......................................... ..243
`7.1 Three-Dimensional Procedures .................................. ..243
`7.2 Three-Dimensional Marine Surveying Method ....... ..249
`7.3 Three-Dimensional Land Surveying Method .......... ..254
`7.4 Other Marine Survey Methods ................................... ..258
`7.4.1 Circular Shooting ............................................. ..259
`7.4.2 Two—Vessel Operations ................................... ..261
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`7.4.3 Reconnaissance Surveying (3-D or 2.5—D
`Surveys) ........................................................... ..262
`7.5 Three—Dimensional Survey Design ............................ ..262
`7.5.1 Sampling ............................................................ ..263
`7.5.2 CMP Binning ..................................................... ..263
`7.5.3 Migration ........................................................... ..265
`Exercise 7.1 ............................................................................. ..268
`Exercise 7.2 ............................................................................. ..27O
`
`Appendices ................................................................................... ..273
`Appendix A ........................................................................... ..273
`The Decibel Scale .......................................................... ..273
`Appendix B ............................................................................ ..276
`Computing Array Responses ..................................... ..276
`Exercise B.1 .................................................................... ..278
`Exercise B.2 .................................................................... ..278
`Appendix C ........................................................................... ..279
`Weighted Arrays .......................................................... ..279
`Appendix D ........................................................................... ..282
`Fourier Analysis ........................................................... ..282
`Exercise D—1 ................................................................... ..288
`
`Index ............................................................................................... ..295
`
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`Preface
`
`In 1983, like so many other geophysical consultants of the day and the
`petroleum exploration industry in general,
`I experienced a downturn in
`exploration activity. In previous years, I had been an electronics engineer, a
`well-logging geologist / engineer, a seismic instrument engineer, a seismic
`crew party manager and an operations manager, after which I had turned to
`consulting. My ”doodle—bugging” career in seismic exploration had been
`every young and agile person's dream~getting lost in Mexican bandit coun-
`try, ducking bullets in Angola and the Philippines, playing soccer in Monte-
`video, cruising around Singapore in a rickshaw, visiting temples in Thailand,
`sitting with maidens in Senegal, dodging limpet mines in Vietnam, losing
`streamers in the North Sea, being incredibly inebriated in the Spratley
`Islands, getting stuck in the middle of the Kalahari Dessert, driving fast rental
`cars along interminable freeways in the United States, experiencing negative
`gravity during plane flights over Alberta, being caught in a force—9 gale in the
`Shetland Islands, losing all belongings after a ”willy—willy” struck our camp
`in Central Australia, depositing the grand piano (and pianist) in an upmarket
`hotel lobby in Singapore and, in the end, having enough money to buy a fast
`car and a house on the same day.
`I wanted to learn more about the seismic industry, which had treated me
`so well and which I loved so much. I had never had a formal lecture in seis~
`
`mic exploration, so like many others, I turned to the education industry to
`learn more about seismic methods so I would be better prepared when the
`industry picked up again. When I began studying exploration geophysics at
`the West Australian Institute of Technology (WAIT) in Perth, I was surprised
`to find there was no textbook that gave an up—to—date, in—depth treatment of
`seismic data acquisition—the area of geophysics in which I had spent most of
`my professional life. There were many good broad textbooks available, but
`none was an adequate lecture text. I realized quickly that I knew more about
`both land and marine seismic operations than was presented in most of the
`available texts. I had worked within and offshore from most countries of the
`
`world during the previous 11 years. The only countries I hadn't worked in
`were the then—communist countries. My initial duties at WAIT were to lecture
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`(part time) in seismic data acquisition while I completed my course work. But
`how could I lecture without some form of text?
`
`So, I assembled notes I had collected over the years and tried to put them
`in some order. I spent three months handwriting a text (there were no per-
`sonal computers in those days) which I then had printed at the WAIT press. I
`finally started teaching seismic data acquisition to students, and I still am
`doing so. Meanwhile, new seismic methods and instruments were being
`developed, and I had to keep my notes up to date. I finally converted the
`handwritten text to a typed (IBM golf—ball) version, for which I am eternally
`grateful to my wife (since I could not type at the time). Each time I updated
`my version of seismic data acquisition methods and printed copies for my
`students, someone would prove another seismic method successful and I had
`to modify the text. The evolution in computing technology and its application
`in seismic data acquisition has been so breathtakingly fast that I haven't been
`able to update the text at the same rate. Therefore, dear reader, I apologize if
`the text still doesn't provide you with all the answers you are seeking, but I
`think it goes a long way toward explaining the fundamentals of our innova-
`tive science.
`
`This book is written primarily for the novice——the person (such as me)
`who was qualified in another area (engineer, geologist, chemist, accountant,
`economist, etc.); it is pitched at students of exploration seismology who want
`to know how and why in simple language. I use it as my main text for final-
`year geophysics honors students at Curtin University of Technology. It also
`can be used as a good basic text for teaching seismic methods.
`The text concentrates on seismic data acquisition in hydrocarbon explora-
`tion. It is light on mathematical methods but heavy on why we do things.
`Consequently, it will be a useful reference book for all those workers on seis-
`mic crews the world over who wonder how we possibly could get a profile
`through the Earth by firing shots over it. (I am still constantly amazed at what
`we can do with seismic.) The text does not cover refraction, shear—wave or
`vertical seismic profiling exploration in any detail because other books do a
`better job on those topics.
`This book was written with Bill Dragoset’s editorship, for which I am eter-
`nally grateful. I thank Western Atlas for allowing Bill time to correct a lot of
`my written words. I also am indebted to a few others for its publication, such
`as my industry colleagues from whom I have learned much, including my
`early field associates at Geophysical Service Inc., those at Geoservice, Aqua-
`tronics, Shell Australia, and Horizon Exploration. My current associates at
`Curtin University, including Norm Uren, John McDonald and Milovan Uro-
`sevic, have individually taught me a lot, as well as my colleagues from the
`University of Houston including Dan Ebrom, K. K. Sekharan, Bob Sheriff, and
`Barbara Murray, with whom I spent most of 1991.
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`As for me, I am a great believer in practicing what you preach. Conse-
`quently, I continue to run my experimental land crew from Curtin University,
`so if you ever need to talk to me on any aspect of seismic data acquisition, call
`me. I'm on e—mail-—evans@geophy.curtin.edu.au—and I'll do my best to
`answer your questions. Oh yes, in return, perhaps you can update me with
`your latest best practice, and between us we can keep this volume updated.
`Happy doodle~bugging.
`
`Brian Evans
`
`Senior Lecturer in Geophysics
`Curtin University of Technology
`Perth, Australia
`
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`Chapter 1
`
`Seismic Exploration
`
`1.1
`
`Introduction
`
`The science of seismology began with the study of naturally occurring
`earthquakes. Seismologists at first were motivated by the desire to under~
`stand the destructive nature of large earthquakes. They soon learned, how-
`ever, that the seismic waves produced by an earthquake contained valuable
`information about the large—scale structure of the Earth's interior.
`Today, much of our understanding of the Earth's mantle, crust, and core is
`based on the analysis of the seismic waves produced by earthquakes. Thus,
`seismology became an important branch of geophysics, the physics of the
`Earth.
`
`Seismologists and geologists also discovered that similar, but much
`weaker, man—made seismic waves had a more practical use: They could probe
`the very shallow structure of the Earth to help locate its mineral, water, and
`hydrocarbon resources. Thus, the seismic exploration industry was born, and
`the seismologists working in that industry came to be called exploration geo-
`physicists. Today seismic exploration encompasses more than just the search
`for resources. Seismic technology is used in the search for waste—disposal
`sites, in determining the stability of the ground under proposed industrial
`facilities, and even in archaeological
`investigations. Nevertheless, since
`hydrocarbon exploration is still the reason for the existence of the seismic
`exploration industry, the methods and terminology explained in this book are
`those commonly used in the oil and natural gas exploration industry.
`The underlying concept of seismic exploration is simple. Man—made seis-
`mic waves are just sound waves (also called acoustic waves) with frequencies
`typically ranging from about 5 Hz to just over 100 Hz. (The lowest sound fre-
`quency audible to the human ear is about 30 Hz.) As these sound waves leave
`the seismic source and travel downward into the Earth,
`they encounter
`changes in the Earth's geological layering, which cause echoes (or reflections)
`to travel upward to the surface. Electromechanical transducers (geophones or
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`WesternGeco v. PGS (IPR2015-00309, 310, 311)
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`PGS Exhibit 2004
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`2
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`SEISMIC DATA ACQUISITION
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`hydrophones) detect the echoes arriving at the surface and convert them into
`electrical signals, which are then amplified, filtered, digitized, and recorded.
`The recorded seismic data usually undergo elaborate processing by digital
`computers to produce images of the earth's shallow structure. An experi-
`enced geologist or geophysicist can interpret those images to determine what
`type of rocks they represent and whether those rocks might contain valuable
`resources.
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`Thus, seismic data acquisition, the subject of this book, is just one stage of a
`multistage process. The full process is known as seismic surveying. Such sur-
`veying involves four discrete stages: survey design and planning, data acqui-
`sition, data processing, and data interpretation. The success or failure of a
`seismic survey often is not determined until the final interpretation stage.
`Because resurveying can be prohibitively expensive, it is of immense impor-
`tance to ensure that all aspects of the survey are performed correctly the first
`time. This means that care in planning and acquiring data is extremely impor-
`tant. This book provides useful information for the first two stages of the sur-
`vey in the hope that it will help the geophysicist to acquire the best possible
`data under each survey environment.
`This chapter describes the fundamentals of seismic data acquisition so that
`the reader will gain the basic knowledge necessary to plan a sensible survey.
`To appreciate fully the various techniques for data acquisition, one must have
`a grasp of both the physics of seismic waves and the data—processing steps
`used to create an image of the earth. Those two topics are reviewed in this
`chapter. The chapter concludes with an overview of survey design consider-
`ations.
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`1.2 Seismic Data Acquisition
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`If the seismic exploration industry were to be described in one word, the
`word would have to be ”innovative.” In continually striving to improve their
`images of the Earth, exploration geophysicists always have been quick to
`adapt new technologies in electronics, computer processing, data recording,
`and transducer design to seismic surveying. Because of this innovative spirit,
`seismic exploration technology has evolved rapidly, especially during the
`past 30 years. Today a well—rounded exploration geophysicist should have a
`basic knowledge of not only geology but also of physics, mathematics, elec—
`tronics, and computer science. Grasping mathematics at a high level was not
`required of the earliest seismologists.
`
`1.2.1 Historical Perspective
`
`The earliest known seismic instrument, called the seismoscope, was pro-
`duced in China about A.D. 100. A small ball bearing was wedged in the
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`WesternGeco v. PGS (IPR2015-00309, 310, 311)
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`PGS Exhibit 2004
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`PGS Exhibit 2004
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
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`1. Seismic Exploration
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`3
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`mouth of each of six dragons mounted on the exterior of a vase (Figure 1). An
`earthquake motion would cause a pendulum fastened to the base of the vase
`to swing. The pendulum in turn would knock a ball from a dragon's mouth
`into a toad’s mouth to indicate the direction from which the tremor came.
`
`In 1848 in France, Mallet began studying the Earth's crust by using acous~
`tic waves. This science developed into what is now called earthquake seis-
`mology, solid earth, or crustal geophysics, which is still a broad area of
`academic research. In 1914 in Germany, Mintrop devised the first seismo-
`graph; it was used for locating enemy artillery during World War I. In 1917 in
`the United States, Fessenden patented a method and apparatus for locating
`ore bodies.
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`The introduction of refraction methods for locating salt domes in the Gulf
`Coast region of the United States began in 1920, and by 1923, a German seis-
`mic service company known as Seismos went international (to Mexico and
`Texas) using the refraction method to locate oil traps.
`As the Search for oil moved to deeper targets, the technique of using
`reflected seismic waves, known as the seismic reflection method, became more
`popular because it aided delineation of other structural features apart from
`simple salt domes. It is said that one of the few good things produced during
`World War II was the technological advances made in seismology in the
`search for oil. Because Germany could not overcome the Allied forces holding
`Middle East oil supplies, it had to develop indigenous oil to sustain the war
`effort. As a result, the Seismos company's budget was increased. The results
`
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`Fig. 1. The seismoscope (after Sheriff).
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`
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
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`PGS Exhibit 2004
`
`PGS Exhibit 2004
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`4
`
`SEISMIC DATA ACQUISITION
`
`included several technical innovations that furthered the development of
`seismic data acquisition equipment and the interpretation of seismic data.
`Beginning in the early 1930s seismic exploration activity in the United
`States surged for 20 years as related technology was being developed and
`refined (Figure 2). For the next 20 years, seismic activity, as measured by the
`US. crew count, declined. During this period, however, the so—called digital
`revolution ushered in what some historians now are calling the Information
`Age. This had a tremendous impact on the seismic exploration industry. The
`ability to record digitized seismic data on magnetic tape, then process that
`data in a computer, not only greatly improved the productivity of seismic
`crews but also greatly improved the fidelity with which the processed data
`imaged earth structure. Modern seismic data acquisition as we know it could
`not have evolved without the digital computer.
`During the past 20 years, the degree of seismic exploration activity has
`become related to the price of a barrel of oil, both in the United States
`(Figure 3) and worldwide. In 1990, US$2.195 billion was spent worldwide in
`geophysical exploration activity (Goodfellow, 1991). More than 96% of this
`(US$2.110 billion) was spent on petroleum exploration.
`Despite the recent decline in the seismic crew count, innovation has con-
`tinued. The late 1970s saw the development of the 3-D seismic survey, in
`which the data imaged not just a vertical cross—section of earth but an entire
`volume of earth. The technology improved during the 1980s, leading to more
`
`lI;r-En.-.r Count
`‘."DIZI
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`1 CID
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`D
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`199:‘
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`194C!
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`1950
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`1960
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`l»/1:91 R I N E Uf'l
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`1980
`1990
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`Fig. 2. US. seismic crew count (Goodfellow, 1991).
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