Seismic Multiple Removal Techniques: Past, present and future. Revised Edition

246 Pages·2013·18.024 MB·English

by  Verschuur, Dirk Jacob

Seismic multiple
removal techniques
past, present and future

Revised Edition

D.J. Verschuur
© 2013 EAGE Publications bv

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ISBN:978-90-73834-56-9

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Preface
When I presented my first 2D surface-related multiple removal results on synthetic data many people
were telling me that it would never work on field data. After the first field data results people said that
it was nice, but that the algorithm was too expensive, such that the method will not become practical.
Ten years later surface-related multiple removal has matured and found its place as one of the
advanced tools in the multiple removal toolbox and today SRME is considered almost a commodity. In
a similar fashion at the 1997 SEG workshop on multiple removal it was argued that full 3D SRME
would never become feasible, as the acquisition geometries of 3D marine seismic data does not allow
to construct the multiples in a truly 3D fashion. A decade later it has been shown by several people
that there are ways to handle the full 3D multiple problem. Thus, the expectation is that within another
decade 3D SRME will be a commodity again and may be included in on-board processing of marine
data. The lesson to learn from this historical overview is that people working at the leading edge of
new technologies should never be worried about ‘details’ like computation power or sampling limits,
as these items are under continuous development as well.
This book supports the one-day EAGE course on multiple removal methods and provides the proper
background information that will help to understand the course contents. I have tried to keep the
mathematical content as simple as possible and where it was needed I made an effort to describe it in a
clear manner and provide illustrative examples. From my point of view, the importance is not in the
mathematical formulations by itself, but in the reasoning that is behind it. Furthermore, I have tried to
emphasise more the physical meaning of certain processes, rather than proving it with rigorous
mathematical derivations. Those can be found in the listed references.
For the contents of this book I have tried to give a broad overview of multiple removal methods that
have been developed within our industry. However, being heavily involved in the development of the
surface-related multiple elimination (SRME) method, more than in any of the other methods, I have
not even tried to balance the contents over the various methodologies. Thus, this book is biased
towards SRME techniques and treats many issues that are related to it. Furthermore, it is also not
complete. There have been so many interesting concepts developed over the last half century, some of
which I only found out when writing this book, that it is hard to capture this in a limited number of
pages. However, wherever possible, I have emphasised the links between the various multiple removal
techniques in order to increase the understanding of these methods.
The current book is a revised version of the initial publication from 2006. Since then, multiple
removal techniques have developed and evolved. I have tried to capture the most important changes
from the last seven years. This means that the later in the book, the more changes can be found,
especially in the referred literature. Still, most of the fundamentals of multiple removal techniques
have not been changed, so the major part of the book is the same as the original version. The most
striking difference is that Chapter 10, on the latest developments in the field of using multiples rather
than removing them, has been expanded and modified according to some recent developments.
I have enjoyed working on this lecture notes and I sincerely hope that this can be found back in its
contents.

Eric Verschuur
Delft, August 2013
Table of contents

Preface                         vi 
Chapter 1.  Multiples .... What's  the Problem?               1  
  Introduction                      1 
  Classification of Multiple Reflections                2  
  Characteristics of Multiples                  7 
  Impact on Seismic Imaging and Interpretation              10 
  Categories of Multiple Removal Methods              12 
  Outline of This Book                    13 
Chapter 2. Multiple Removal Based on Move‐out and Dip Discrimination         15 
  Introduction                      15 
  Principle of Multiple Removal by Move‐out Discrimination          15 
  F‐K and Radon Transforms                  17 
  Multiple Removal by Filtering in the F‐K or Radon Domain         27  
  Multiple Suppression via the Parabolic Radon Domain            28 
  Towards High‐Resolution Radon Transforms             30  
  Limitations of Multiple Removal by Move‐out Discrimination          34 
  Multiple Removal by Target‐Oriented Dip Filtering           37 
Chapter 3. Predictive Deconvolution                  40 
  Introduction                      40 
  Convolution and Correlation Concept                40 
  Designing Adaptive Filters by Least‐Squares Optimisation          44 
  Predictive Deconvolution Basics                 49 
  Extending the Predictive Deconvolution Concept           55 
Chapter 4. Multiple Removal by Wave Field Extrapolation           65 
  Introduction                      65 
  Forward and Inverse Wave Field Extrapolation              65 
  Multiple Prediction by Wave Field Extrapolation             72 
  Application in the Wave Number and Linear Radon Domain         81  
Chapter 5. Principles of Surface‐Related Multiple Elimination           84 
  Introduction                      84
Derivation of SRME for the 1D Situation               84 
  Formulation of SRME for the 2D and 3D Situation           92 
  Adaptive Version of SRME                  96 
  Iterative Implementation of SRME                99 
  Relation between Multiple Prediction and Subtraction Methods        103 
Chapter 6. Practical Aspects of Surface‐Related Multiple Elimination         105 
  Introduction                      105 
  Effect of Missing Data for SRME                 105 
  Shallow Water Multiple Removal Strategy              116 
  Multiple Removal for Land Data                120  
  Application of SRME in Different Data Domains             123 
Chapter 7. Adaptive Subtraction of Predicted Multiples              131 
  Introduction                      131 
  Least‐Squares Subtraction Strategies               132 
  Alternative Subtraction Techniques               144 
Chapter 8. Towards 3D Multiple Removal                151 
  Introduction                      151 
  Multiples in Complex 3D Environments               151 
  3D SRME: Theory                    158 
  3D SRME: Solutions via Data Interpolation              162 
Chapter 9. Internal Multiple Removal                  174 
  Introduction                      174 
  Internal Multiple Removal by Move‐out Discrimination           176 
  Extending the SRME Concept to Internal Multiples            178 
  Internal Multiple Removal by Inverse Scattering            183 
  Layer‐Related Internal Multiple Elimination             186 
  Hybrid and 3D Internal Multiple Removal Strategies           191 
  CMP‐Oriented and Post‐Stack Strategies               192 
Chapter 10. Removing or Using Multiples?                195 
  Introduction                      195 
  Transforming Multiples into Primaries               195 
  Estimation of Primaries by Sparse Inversion             203 
  Including Multiples in the Migration Process             207
Including Multiples in the Inversion Process             216 
  The Multiples May Become Our Friends...              216 
Biography                        218 
References                        219 
Acknowledgements                      233 
Index                          236
Chapter 1 Multiples .... What’s the problem?
Introduction
Seismic reflection measurements are typically made with sources and receivers positioned at the
surface of the earth, while recording reflections from inhomogeneities in the subsurface. Seismic
imaging algorithms aim at focussing the energy back to the reflection points in the subsurface, thus
creating an image of the reflection properties of the earth. Most of these imaging algorithms make the
assumption that all scattered energy has been reflected in the subsurface only once, such as shown by
the yellow lines in Figure 1.1. In practice, however, each reflecting or scattering object in the
subsurface does not make any difference between waves travelling downward or upward. With other
words, acoustic waves that are on their way back to the surface will pass shallower inhomogeneities,
which results in a secondary, downward scattering of energy. As a result multiple reflection will occur,
which may eventually end up at the seismic receivers, as indicated by the blue lines in Figure 1.1.
These multiple reflection events are normally considered as noise and need to be removed from the
seismic data in order to avoid confusion in the interpretation of the seismic images at a later stage. This
is done in the seismic data processing stage by dedicated procedures, which are often referred to as
multiple removal or multiple suppression methods.
This course book will treat the most common methods in use today for the removal of multiple
reflections. But before multiple removal methods are introduced we will take a closer look at the
multiple reflections that occur in seismic data. We will categorise the different types of multiples and
see how multiples can be recognized in seismic data.
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Figure 1.1: Primary reflections have only o ne upward reflection in the sub surface (yellow lines) and multiple
reflections have at least one downward reflection (blue lines).
Classification of multiple reflections
There are several ways to categorise multiple reflections. First, we will consider the interface where
they have their shallowest downward bounce. In Figure 1.2a two multiple reflection paths have been
drawn. The first multiple has one downward bounce at the first reflector below the surface. This we
call an internal multiple related to the first reflector (e.g. the water bottom for the marine case). The
second multiple path in Figure 1.2a has two downward bounces at different reflectors: one at the
surface and one at the first reflector. We will relate this multiple reflection event to the shallowest
interface where downward reflection takes place, so in this case it is a surface-related multiple. With
this in mind, surface-related multiples can be defined as those multiples, which do not exist anymore if
the surface of the earth becomes transparent for acoustic energy. This is illustrated in Figure 1.2b. In
the case of internal multiples, all reflectors above and including the interface of reference should
become acoustically transparent before they disappear. With the same reasoning, the first event in
Figure 1.3 is a surface-related multiple and the second event in Figure 1.3 is a water bottom-related
internal multiple, as it will disappear when both the surface and the water bottom would become
acoustically transparent.
Figure 1.2: a) Two types of multiple reflections. b) Surface-related multiples are those multiples that disappear
when the free surface would become transparant.
Figure 1.3: Multiples are classified by their shallowest reflection boundary. a) Example of a surface-related
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multiple. b) Example of a water bottom-related internal multiple.
Some multiple removal methods address specific types of multiples. Therefore, it is good to divide
the surface-related multiples into sub-categories. In Figure 1.4a, b and c three types of surface-related
multiples are illustrated, where for convenience the first layer is assumed to be a water layer. The
multiples depicted in Figure 1.4a are referred to as water layer multiples or water bottom multiples,
which represents energy that propagates up and down in the water layer without ever travelling below
the water bottom. Figure 1.4b describes water layer reverberations, which are events that have
reflected below the water bottom once, and have one or more multiple reflections in the water layer.
Note that these reverberations can occur at the source side, at the receiver side or both. Next, there are
surface-related multiples that have two or more reflections below the water bottom. This category does
not have a specific name, and are referred to as ‘other surface-related multiples’. These multiples can
be important in the case of one or more strong reflecting structures below the water bottom, such as the
top of a salt layer. Note that a multiple with two or more sub-bottom reflections and with one or more
additional reverberations in the first layer could be categorized as being into both categories ‘water
layer reverberations’ and ‘other surface-related multiples’. For consistency, they are referred to – if at
all – as reverberations, as that is the shallowest part of such a surface-related multiple. Finally,
multiples that have no downward bounce at the surface are called internal multiples (Figure 1.4d).
Figure 1.4: Different categories of multiples. a) Multiples that bounce within the first layer. b) Multiples that have
at least one bounce in the first layer. c) Multiples related to the surface, but that have no bounce in the first layer.
d) Internal multiples. Note that a), b) and c) are all surface-related multiples.
For a field dataset all these types of multiples have been indicated. Figure 1.5 shows a stacked
section from a 2D seismic marine line in the Nordkapp area, which is the most northern part in
Norway. The line crosses two salt domes, which can be recognized in the stack as the structures
around CMP number 900 and around CMP number 2400. As the water bottom is reasonably flat, the
water layer multiples are recognized as horizontal events that cross the reflections of the geologic
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