Seismic Depth Imaging and Anisotropic Velocity Model Building
|Mr Etienne Robein (ERT, Pau, France)|
|Geophysics – Surface Imaging|
|The EET 4 book is available in the EAGE Bookshop|
|10 CPD points|
ANISOTROPY DEPTH MIGRATION INVERSION KIRCHHOFF MIGRATION OFFSET REFLECTION TOMOGRAPHY WAVE PROPAGATION
A short version of this course has been recorded as an E-Lecture. Watching this video will give you a clear introduction of what the course is about and it will help you to prepare yourself if you are going to attend it!
As the search for new resources forces to maximize the production of discovered reservoirs and explore new ones in domains that are increasingly complex, seismic imaging is becoming more and more important.
Seismic imaging is inherent part of the data processing sequence that aims to produce clear and accurate images of the Earth's subsurface suitable for interpretation by geoscientists.
This course will provide the audience with a unified overview of today's most popular seismic depth imaging techniques used in the oil and gas industry. These requires an estimate of how fast the seismic waves travel at any given point in the Earth and at any direction (anisotropy): the velocity model. Recent advances in seismic acquisition, imaging technology and high-performance computing allow us to correctly assess a much greater complexity of subsurface models and consequently, improve the accuracy of seismic images and detect structures that were previously invisible.
The course will present in simple terms (cartoons rather than equations!) the principle of different techniques in each class of methods (Kirchhoff, Beam Migrations, WEM, RTM), while pointing out their respective merits and limitations. Similarities and differences between time- and depth-imaging will be briefly reviewed. Special emphasis will be on methods used to build the necessary anisotropic velocity models. Both ray-based techniques (linear and non-linear tomography) and wavefield extrapolation-based ones, including full-waveform inversion, will be addressed.
The relationship between recent developments in acquisition and imaging on the one hand and interpretation and imaging on the other will also be stressed.
Upon completion of the course, participants will be able to:
- Evaluate the potential value of the principal techniques used in seismic imaging;
- Understand differences between time- and depth-processing and select the best option for a given problem;
- Be aware of key steps and issues in building anisotropic depth velocity models with borehole control;
- Understand the complementarity between ray-based and wavefield extrapolation-based velocity model building;
- Be aware of current results and issues in full-waveform inversion;
- Evaluate the impact of recent breakthroughs in data acquisition on seismic imaging.
- An image of the changes in elastic properties in the subsurface;
- Various techniques to simulate wave propagation: Ray tracing, Gaussian beams, Wavefield Extrapolation;
- An introduction to seismic anisotropy; Thomsen’s parameters; VTI, TTI,TOR models;
- Illumination; Signal/noise; Resolution; Accuracy; Amplitude fidelity;
- Wavefield separation; deghosting; broadband seismic;
- Data sorting for imaging: shots; binning; common offset; offset vectors; CIGs.
Ray-based Kirchhoff Depth Migrations (KPreSDM)
- Principles of Kirchhoff depth migration in the Common-Offset domain;
- Common Image Gathers;
- What if the velocities or anisotropic parameters are wrong;
- Kirchhoff summation in the Scattering Angle domain.
Time processing: Kirchhoff migration in ‘vertical time’ (PreSTM)
- Definition and use of ‘vertical time’;
- The ‘multi-1D’ assumptions made in PreSTM: benefit and impact on the seismic image;
- Definition and measurement of the Vnmo and Eta fields;
- CRS and multifocusing (velocity independent) methods. Zero and non-zero offset.
The various Beam Migrations
- The concept of ray-based migration of ‘locally coherent events’ in the shot and common offset domains;
- The use of tau-p transform;
- Conceptual differences between Kirchhoff and Beam migrations
- A range of methods to build the image and increase efficiency: fast beam, Gaussian Beam, controlled beam migrations;
- Comparisons on real cases; discussion of respective merits and limitations.
Velocity Model Building (VMB) by Ray-based tomography
- Definition, flowchart and principles of linear and non linear (‘slope’) tomography;
- Non-flatness or Residual Move Out analysis of Common Image Gathers;
- A variety of ‘strategies’ and VMB flowcharts: examples and discussion;
- Accounting for anisotropy: estimation of the delta and epsilon fields with borehole control.
Wavefield extrapolation-based methods: WEM and RTM
- Claerbout’s imaging principle;
- Principles of one-way Shot point migration ‘WEM’. Synthetic and real case comparisons: merits and limitations;
- The RTM sequence illustrated on a synthetic example; two-way propagation; numerical issues; frequency limitation in RTM;
- Benefits of the ‘two-way propagator’ (turning waves; prism waves): synthetic and real case examples;
- Illumination studies to improve RTM results;
- RTM and the migration of multiples.
Wave-equation based Velocity Model Building and FWI
- Scattering Angle CIGs after RTM: Poynting vectors; Extended Imaging condition;
- VMB after RTM. The case of subsalt imaging. Recent examples and advances;
- Concept, flowchart and techniques of Full Waveform Inversion (FWI);
- Main issues in FWI: numerical, initial model, cost function. Synthetic and real case studies: comparison and discussion;
- Impact of recent advances in acquisition (low frequencies).
The course is aimed at geoscientists involved in exploration and production projects where seismic play a role and who wish to:
- Learn more about seismic imaging concepts and the terminology used by seismic processors;
- Be aware of the variety of techniques and tools at our disposal in seismic imaging;
- Have a well-argued selection of the imaging method to apply to the seismic data acquired for their projects;
- improve their critical view on the benefits and limitations of the seismic data sets they are using in their projects;
- Have a better appreciation of what they can expect from reprocessing vintage data sets with modern tools.
The course will also benefit students who want to have a first acquaintance to reflection seismic in general and seismic imaging in particular.
The course can be understood by geoscientists with a moderate mathematical background. Physical concepts are presented without equations but with a maximum of simple schemes and animated graphic illustrations. However, some basic knowledge of wave propagation theory may help. A comprehensive list of references is given in the book and updated in the presentation for those who are interested in more rigorous and mathematical approaches.
About the instructor
Etienne Robein graduated from Ecole Nationale Supérieure d'Aéronautique et Espace and Ecole Nationale Supérieure Pétrole et Moteurs / IFP in Paris in 1973. He started his career with Shell in the Hague, before joining Elf, now Total, where he has worked on operational, research and managerial assignments in France, Italy, the UK and Azerbaijan. His professional experience covers seismic acquisition, processing and interpretation. His last position with Total was R&D programme manager in Geology and Geophysics. Etienne now works as a freelance tutor in Geophysics, having set-up his own Company “ERT”.
Etienne is the author or co-author of several presentations in International Conferences, including the SEG, EAGE, WPC, AAPG, and Petroleum Geology Conference and he contributed to the EAGE’s “Distinguished Lecture Programme” and “Education days”. In 2003, he published a text book on “Velocities, Time-imaging and Depth-imaging in Reflection Seismics,” which became a best-seller EAGE Edition. Etienne was President of EAGE in 2000. He was also Chairman of EAGE’s Research Committee, member of the EAGE Awards Committee and Europe’s representative at the SEG Council.
Explore other courses under this discipline:
Instructor: Prof. Tariq Alkhalifah (KAUST)
The course starts by introducing the fundamentals of full-waveform inversion (FWI) starting from its basic definition. It focuses on the model update issues and provides analysis of its probable success in converging to a plausible model. In the course we will discuss the many challenges we face in applying FWI on seismic data and introduce modern day proposed solutions to these challenges. The focus of the course will be on FWI applied to anisotropic media. As a result, the course will also introduce anisotropy, its optimal parametrization and wavefield simulation in such media. Practical multi-parameter inversion for anisotropic parameters requires an optimal FWI setup. We will discuss such a setup, which includes the proper parametrization of the medium and data access scheme necessary for a potential convergence to a plausible anisotropic model.
Instructor: Dr Gerard Schuster (KAUST)
This one-day course is designed for a broad range of seismic researchers, data processors, and interpreters working in the petroleum industry. The course teaches the principles of seismic interferometry, ambient noise seismology and their applications to surface seismic, VSP, and OBS data. The ultimate objectives are to enable geophysicists to evaluate the potential of seismic interferometry in uniquely solving their problems.
Instructors: Prof. Evgeny Landa (Tel Aviv University) and Dr Tijmen Jan Moser (Moser Geophysical Services)
Diffractions have been identified as the key seismic manifestation of fractures and other small-scale reservoir heterogeneities. This two-day course will present the current state-of-the-art of diffraction technology and put this in context by a review of its past developments. The course will cover both forward diffraction modeling and diffraction imaging. Case studies of diffraction imaging will be presented covering applications in seismic exploration and other areas of geoscientific interest.
Instructor: Dr Ruben Martinez (Reservoir Geoscience)
This course has two main segments. In the first segment, the participant will understand the basic concepts behind the tools commonly employed in velocity model building and depth migration.
In the second segment, the participant will learn how to use these tools for building velocity models and generate seismic images in depth using practical work flows for a variety of complex geologic scenarios. At the end of the course, an overview of the emerging depth imaging technologies is presented.
Instructor: Prof. Evgeny Landa (Tel Aviv University)
While depth imaging play an increasing role in seismic exploration, data analysis and imaging in time domain play an important role. Moreover, for complex models that request the use of prestack depth migration, time imaging usually constitutes a key first step. The proposed course discusses: a) data analysis and imaging based on new procedures such as Multifocusing and Common Reflection Surface; b) diffraction Imaging based on diffracted energy targeting to image small scale subsurface objects; c) imaging without precise knowledge of the subsurface velocity model (path summation); d) pitfalls and challenges of seismic inversion.
Instructor: Mr Etienne Robein (ERT)
The course will present in simple terms (cartoons rather than equations!) the principle of different techniques in each class of methods (Kirchhoff, Beam Migrations, WEM, RTM), while pointing out their respective merits and limitations. Similarities and differences between Time- and Depth-Imaging will be briefly reminded. In parallel, special emphasis is put on methods used to build the necessary anisotropic velocity models. Both Ray-based techniques (linear and non-linear tomography) and wavefield extrapolation-based ones, including Full Waveform Inversion, are addressed.
Instructor: Prof. Dr Dries Gisolf (Delft Inversion)
This two-day course will start with an introduction and a short recap on complex integral transforms (Fourier, Laplace, F/K and linear Radon). Followed by topics on: - The acoustic wave equation in inhomogenous media - Integral representations of the acoustic wave equation; Kirchhoff-Rayleigh and the Scattering Integral (Lippmann-Schwinger) - The AVO data model; Zoeppritz reflection coefficients - Linear inversion of AVO data including regularisation; synthetic and real data examples - The non-linear data model for inversion; data equation and object equation; iterative, multiplicatively regularised inversion - Applications based on an elastic full-wavefield non-linear data model; realistic synthetic reservoir study, real data case studies including low-frequency model extraction and seismic-to-well matching. Synthetic time-lapse example.
Instructor: Mr Piet Gerritsma (Gerritsma Geophysical Training and Consultancy)
The process of migration, whereby a proper image in time or depth of the subsurface is obtained, is directly related with the velocity model that both serves as input for the migration process as well as is the result of such a migration. Therefore migration and velocity model building are intimately related processes and often applied in an iterative mode. This course gives an overwiew with theory and implementation of the representative migration algorithms as well as of the multitude of ways to build and update subsurface velocity models.
Instructor: Prof. Dr Dries Gisolf (Delft Inversion)
This course presents a systematic approach to imaging of acoustic reflection data and the extraction of media property information from the image amplitudes, based on wave theory. Although the approach is valid for a wide range of acoustical frequencies and applications, there is a bias towards seismic imaging.