The Interpreter's Guide to Depth Imaging

by Dr. Scott MacKay

Duration: Two days

Intended Audience: Intermediate level

Prerequisites (Knowledge/Experience/Education Required): Interpreters incorporating depth imaging into their exploration and exploitation evaluations. Training is conducted with a combination of lectures, demonstrations, and test sets. Participants should be familiar with the seismic method and have several years of interpretation experience.

Summary: An intuitive approach to the theory and practical applications of prestack depth imaging. The instructor demonstrates the quality controls used to promote stable solutions and methods for well calibration, constraining anisotropic depth migration, and the power and pitfalls of inversion for azimuthal properties that yield geologically-reasonable results.

Learner Outcomes: Participants will gain an understanding of how to effectively design, guide, and quality control depth-imaging projects in a variety of geologic settings and be able to:

  • Categorize the various time-to-depth conversion methodologies
  • Differentiate between time and depth migration
  • Distinguish between commonly used migration algorithms
  • Evaluate migration-parameter tests
  • Appraise the form of velocity updating (tomography) appropriate for the geology
  • Define the target velocity resolution for tomography and the related imaging grids
  • Validate and correct the database using well and seismic ties
  • Plan and review QCs for iterative velocity updates
  • Assess the methods used for determining anisotropic parameters
  • Perform well and seismic calibration
  • Evaluate attributes such as inversion and directional lithology estimates
     

1: Review of Vertical Time-to-Depth Methods

  • Velocity field characterization
  • Single- and multi-layer methods
  • Error analysis and pitfalls

Test Sets:

Time-to-depth conversion and mapping problems

2: Time and Depth Migration: Comparisons

  • General discussion of time and depth migration theory

Test Sets:

Industry examples and class discussions of participant experiences

3: Migration Algorithms: Theory and Practice

  • Kirchhoff, Gaussian Beam, 1-way Wave Equation and 2-way (Reverse Time)
  • Offset and angler domains for Common Image Point Gathers
  • Anisotropy and Multi-component

Test Sets:

Ray-tracing problem sets and case history reviews

4: Migration: Parameter Selection

  • Kirchhoff travel times and Wave Equation imaging conditions
  • Amplitudes, aliasing, and aperture
  • Regularization and illumination

Test Sets:

Ray trace, amplitude, aliasing, and aperture calculations with spreadsheet calculations

5: Tomographic Velocity Analysis

  • Layer- and grid-based ray methods
  • Full waveform inversion
  • Tomographic limitations and stability

Test Sets:

Simple tomographic examples demonstrating uniqueness and stability

6: Depth Imaging Grids

  • Depth/Velocity: Visualization and velocity representation
  • Travel times/Propagation: Summation curves and/or wavefield extrapolation
  • CIP picking/Tomography: Data input to tomography and solution grid

Test Sets:

Evaluate various scenarios using established criteria

7: Well/Seismic Database Validation

  • Determine data polarity and phase (synthetic ties and VSPs)
  • Basic depth-conversion QCs to encounter data discrepancies

Test Sets:

QCs presented with various problems

8: Iterative Depth Imaging: Quality Control

  • QCs for creating the initial velocity model
  • Iterative tomographic updates and target-velocity resolution
  • Setting up an intuitive review of the iterative process

Test Sets:

QCs presented with associated data sets

9: Anisotropy

  • Parameterization (Vz, delta, epsilon, VTI/TTI)
  • Velocity and parameter updates including directional anisotropy (HTI)

Test Sets:

Review and discuss benefits and pitfalls of attributes from isotropic and anisotropic PSDM

10: Well Calibration

  • Working in the time domain and updating the time/velocity model
  • Conversion of time data to calibrated depth
  • Uncertainty measures (Stochastic prognoses)

Test Sets:

Various calibration exercises in spreadsheet and map form

11: Attributes

  • Poststack: amplitudes, curvature, coherence,
  • Prestack: AVO, elastic inversion, brittleness
  • AVO with Azimuth and other Horizontal Transverse Isotropy (HTI) measurements

Test Sets:

Review benefits and pitfalls of attributes from PSTM and PSDM

Instructor Biography:
Dr. Scott MacKay