Applied Geological Subsurface Imaging and Velocity Model Building

Course Description

Velocity is one of the most important parameter that can be derived from the seismic data. Velocity values are indicative for layer identification and thus convey rock properties. Moreover, velocities relate the seismic measurements that are in (two-way) traveltime to the end product of seismic data processing, i.e. the depth picture of the subsurface that can be obtained via migration or seismic imaging. New developments in acquisition geometries enable the determination of velocities with greater accuracy and also require to take into account anisotropy. The relationships between elastic constants and velocities are explained; this includes the phenomenon of anisotropy. In the end it is the wave equation that describes all wave propagation phenomena. Different types of velocities play a role during the processing sequence; stacking and migration being the most important ones. Migration or seismic imaging is the typical end product of conventional seismic data processing. 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. DMO (dip moveout) can be considered as an intermediate process; it contains elements of migration and can be used in velocity model building. The implementation of migration is characterized by a multitude of methods and algorithms; there is also a variety of methods to build a velocity model. By the same token there is a number of DMO algorithms. This course gives an overview of all aspects of velocity that one encounters during seismic data processing, of the migration principles, methods and algorithms, of the velocity model building principles and methods as well as of the different DMO algorithms. In addition VSP data acquisition and processing will be discussed. During the course and at the end a number of representative case studies and examples will be shown to illustrate the material covered during this course.

 

 

Course Objectives

Participants will get a full understanding and appreciation of the different types of velocity and corresponding methods for their measurement, especially interval velocities and their relationship with rock properties and prestack depth migration. They will become familiar with the different methods of migration and their subsequent implementation. They will be able to judge the strong and weak points of each algorithm and they can select their proper parameters. They can select and apply the method that is most appropriate for velocity model building based on the data, pre-processing results, geological information and stated objectives.

 

 

Who Should Attend

Geophysicists – processing and interpretation –, geologists, and petrophysicists who need to understand how the various types of velocity information can be derived from seismic data and who need to understand how subsurface images are generated.

As the material covers all theory in association with present day practicalities made possible by new developments, this course is relevant for those who are fresh from the university as well for those who like to be updated on the newest developments. 

 

 

Continuing Professional Development

35 HOURS CPD

 

 

Course Content

Introduction

1. Developments in seismic data acquisition and their impact on processing

2. Stress-strain relationships, elastic constants and rock physics

3. The wave equation, acoustic and elastic

4. Overview of seismic data processing practice

 

 

Velocity analysis, stacking and stacking velocities

1. Definitions of various types of velocity

2. Traveltime expressions for paraxial rays

3. Velocities and wavefront curvatures

4. Expressions for azimuth dependent stacking velocities

5. Stacking velocity analysis: CVG, CVS, and Semblance

6. NMO stretch

7. The common-reflection-surface (CRS) stack

8. Analytical time-depth relationships

 

 

Anisotropy

1. Introduction and definition of anisotropy

2. The stress tensor, the Voigt notation and symmetries

3. Plane wave solutions and the Christoffel equations

4. Phase velocity and group velocity

5. Relationship between Wave surface and Slowness surface

6. Reflection and transmission in anisotropic media

7. Shear-wave splitting

8. Vertical Transverse Isotropy (VTI)

9. Horizontal Transverse Isotropy (HTI) and azimuthal anisotropy

10. Anisotropy from seismic survey design and processing

 

 

 

Migration: principles and algorithms

1. Geometric approach to migration

2. Examples

3. Resolution before and after migration

4. Aliasing

5. Definition of time migration and depth migration

6. Wavefield extrapolation

7. The imaging conditions

8. Shot profile migration and survey sinking migration

9. Extended imaging conditions

10. Migration algorithms in the (k,f)-domain:

  • (k,f)-migration
  • Phase-shift migration, Phase-shift-plus-interpolation migration, Split-step-Fourier migration

11. The Kirchhoff integral, the Rayleigh integral and Green’s functions

12. Kirchhoff (= summation or diffraction stack) migration

13. Migration by double focused array synthesis

14. Gaussian beam migration

15. Reverse time migration – RTM

16. Migration and demigration

 

 

DMO (dip moveout) and PSI (pre-stack imaging)

1. Definition, effects and objective

2. The DMO equation and DMO impulse response

3. 3D DMO

4. PSI (pre-stack imaging): principle and equations

5. DMO and velocity analysis

6. AMO: azimuth moveout

 

 

Velocity model building and updating

1. Minimal data sets and common image gathers – CIG’s

2. Iterative velocity model building with CIG’s

3. The migration conditions

4. Migration and traveltime inversion

5. Migration and demigration

6. Normal incidence wavefront curvature and stacking velocity

7. Velocity model parameterization

8. Velocity model building methods:

  • coherency inversion or model based stack
  • map migration
  • dynamic map migration (DMM) or curvature inversion
  • stereotomography
  • traveltime inversion (TTI)
  • traveltime inversion in the migrated domain (TIMD)
  • common focus panel (CFP) analysis
  • tomographic velocity model building
  • depth focusing analysis (DFA)
  • WEMVA (wave equation migration velocity analysis)
  • differential semblance optimization (DSO)
  • full waveform inversion (FWI)

 

 

VSP seismic

1. VSP acquisition geometries

2. The processing sequence for VSP data:

  • Wavefield decomposition
  • Deconvolution
  • Migration

 

 

Case studies – Examples

. Tomography

. Full wave inversion

. Velocity model building

. Parametric velocity estimation

 

 

Duration

5 days
 

Location

Date

 

Dubai, United Arab Emirates

 

 

19-23 November 2017

 

London, United Kingdom

 

 

12-16 March 2018

 

Houston, Texas, United States

 

 

14-18 May 2018