An Introduction to: Velocity Model Building

image of An Introduction to: Velocity Model Building
  • By Ian F. Jones
  • Format: EPUB
  • Publication Year: 2010
  • Number of Pages: 296
  • Language: English
  • Ebook ISBN: 9789073834958

This book sets out to give the reader a non-mathematical understanding of the basic principles of migration and of building a velocity model of the earth’s subsurface. The intended readership includes anyone who has to work with, or to understand, how contemporary seismic images are created: what are the underlying principles and pitfalls? How is a velocity model typically built and what are the consequences of not getting it right?

Concepts such as uncertainty and non-uniqueness are discussed as are the ways in which these topics translate to risk-reduction and reliability in the final image. The different ways of representing a velocity model are reviewed as are the techniques used for picking velocity and anisotropy related information. A review of the principles of tomography is presented, to familiarize the reader with the techniques that underpin all contemporary velocity model update. Also, the physics behind anisotropy and its consequences for obtaining images in ?true? geological depth are discussed.

An historical overview of velocity model building techniques over the past 30 years is presented to give the reader a feel for how the black art of model building has evolved in tandem with the increase in computer power and the emergence of powerful interactive graphics, covering the evolution from a purely linear compartmentalized industrial process towards a fully interactive multidisciplinary approach to iteratively building a reliable subsurface velocity model.

The book concludes with a look at emerging and future trends: the promise of velocity-independent imaging and the potential of full waveform inversion.

Table of Contents

Title Page
Copyright Page
1. Introduction: from recorded data to images

What migration sets-out to do
Time versus depth
Classes of migration: waves versus rays
Integral versus differential techniques
Domains of application
Evolution of migration schemes
One-way versus two-way wave propagation
The migration operator and impulse response
Algorithm noise in integral techniques

2. Why do we need a detailed velocity model?
The limitations of time migration and benefits of depth migration
What does the migration algorithm ‘see’: honouring the velocity field
What algorithm where?

3. How detailed can we get in building a velocity model?
Precision and accuracy
Uncertainty, non-uniqueness, and ambiguity
Limits on resolution
Quantifying error
Is it correct? - imaging pitfalls and velocity model QC

4. Velocity Model Representation and Picking
Layer-based, gridded, and hybrid models
Density of picks and automation
Picking methods
Stack-power and semblance
Differential semblance
AVO-tolerant picking
Locally coherent event picking
CRS picking and multifocusing
Picking pitfalls

5. Inversion and tomography
What is inversion?
What is tomography?
Why we need tomography: sub cable velocity variation
Resolution scale length
Types and domains of tomography
Traveltime (ray) tomography
Traveltime (ray) tomography in the migrated domain
Waveform (diffraction) tomography
Tomography issues

6. Incorporating Anisotropy
How is it manifested?
Relationship to other parameters
Building anisotropic models
Starting from isotropic velocities
Starting from scratch
Azimuthal anisotropy and fracture detection
Azimuthal heterogeneity and multi-azimuth tomography

7. Velocity Model Update Through The Ages
Isotropic model building and “depthing’
Model updating: picking and inverting
Evolution of non-tomographic techniques
Map migration
Coherency inversion
The Deregowski loop
Wavefield extrapolation and focusing analysis
CRP gather scanning and image scanning techniques
Evolution of tomographic techniques
Stereo Tomography
CFP analysis

8. Iterative tomographic update
The iterative model update loop
Including a well data base
What does tomography need to accomplish?
Layered, gridded, and hybrid tomography
Styles of layer constraint for hybrid tomography
Salt and basalt model building
Finite offset versus parametric inversion
Inverting for heterogeneity with azimuthal tomography

9. Near-surface and near-seabed effects
Land environments: topography and statics
Traveltime sampling and short wavelength statics
Marine environments
Simple versus complex water layers
Deep water near-sea-bed anomalies
Geomechanical modelling

10. The future?
Addressing the ‘full wavefield’
Incorporating non-seismic data
“Full waveform inversion, waveform tomography, diffraction tomography
Wavepath tomography and WEM-VA
Model independent imaging
Path integral migration
Seismic interferometry
Interferometric imaging
Inverse scattering migration
CRS picking and multi-focusing



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