A Practical Understanding of Pre- and Poststack Migration

by John C. Bancroft

Duration: Two to five days

Intended Audience: All levels

Prerequisites (Knowledge/Experience/Education Required): This course is designed to be followed by anyone with a broad knowledge of seismic processing. No specific knowledge or background is required as instruction is from basic principles and figures with very little math.

Summary:
These two courses present the basic methods of migration in a simple manner and uses diagrams and figures to illustrate principles.  The first course is three days and covers the basic algorithms of poststack migration then discusses issues related to migration such as topography, frequency content, or parameters, to build a foundation for the following prestack course. The second two day course deals with the prestack nature of migration and its superior capability of imaging the subsurface.

A feature of these courses is the nature in which the material is presented. Most pages in the notes contain a text page on the left with accompanying figures on the right. The concepts are presented in an intuitive graphical manner without detailed mathematics that can obscure the fundamental concepts. Some mathematics is included to illustrate the simplicity of the algorithms. Numerous geometrical constructions are included in the notes to illustrate the simplicity of migration algorithms.

The course is designed for all geophysicists, independent of their background. Each participant will have an understanding of the basic algorithms and should be able to communicate freely between processing specialists and seismic interpreters. Those with computer skills will be able to write their own migration programs.

Course Outlines:

This version of the course will include laboratory exercises that will evaluate modelling and migration programs.

Poststack Course Description (Three days)

• Zero offset seismic modelling is introduce first because of it simplicity as it represents a forward process. These modelling concepts will later become part of the migration process itself.
• A review of the Fourier Transform, aliasing, interpolation, velocity concepts, and the difference between time and depth migration are then presented.
• The various migration algorithms are introduced as the inverse process of modelling.
• Practical methods for evaluating the migration algorithms are presented.
• Various topics that affect the migration qualities are examined, especially the problems associated with rugged topography.

Prestack Course Description (Two days)

• Prestack modelling with variable source receiver offsets is studied along with some prestack models.
• Dip moveout is evaluated, especially the conditions under which it is a useful process.
• Prestack algorithms of source (shot) records and constant offset section are compared with other prestack algorithms.

Instructor Biography:
John C. Bancroft