Velocities For Depth Conversion And Imaging

Seismic data is acquired in time – the time taken for the sound to travel from the source to reflectors and to return to receivers. However, wells are drilled in depth, not time. Variations in velocity can distort the depth, size, and shape of possible reservoirs. Therefore, conversion from time to depth is needed for a clear picture of the prospect and the risks involved. This course will teach you how to use velocity information and structural inputs to build a consistent velocity model and/or calibrate ones that have been created during seismic data processing.

Course Objectives

  • How To Understand the various types of velocities, their calculation, and the validity of their interpolation and extrapolation
  • Compare, quality control, smooth, and combine the various velocity types into an integrated velocity model
  • Validate model quality by examining the changes in velocity needed to tie the seismic
  • Use the model to convert horizons, faults, and seismic data from time to depth
  • Understand at an introductory level, how velocity models are used for other studies such as forward modeling and pore-pressure prediction
Discipline: Geophysics
Level: Advanced
Duration: 5 Days

Velocity: definition and comparison of the many types of velocity including average, interval, RMS, stacking, migration, P-wave, and S-wave

Velocity Inputs: accuracy and regional extent of each, including check shots, VSPs, sonic logs, time/depth functions, well picks and pseudo velocities, seismic velocities, and horizons for structural control

Synthetic Seismograms: creation, upscaling, and tie to seismic data. Advanced synthetics including synthetic gather creation, Zoeppritz equations, AVA, and AVO

Matching Synthetics to Seismic: calibrating the seismic data to the well data

Seismic Velocities: semblance analysis, velocity picking, multiples, and how seismic velocities differ from well velocities

Migration and Migration Velocities: introduction to pre- and post-stack algorithms, tomography, and iterative velocity analysis

Velocity Model Building: workflows to integrate stacking velocities, time/depth curves, well picks associated with seismic horizons (pseudo-velocities), and structure from horizons

Time-to-Depth Conversions: vertical stretch, inverse raytracing, migration, and uncertainty

Introduction to Advanced Topics: anisotropy, pore-pressure prediction, geostatistics, and forward modeling

Early-career geoscientists and engineers, especially seismic interpreters, and anyone who needs to understand the basic theory and procedures for creating velocity models and converting seismic data from time to depth. This is a foundation level course. It is neither designed nor paced for the experienced velocity modeler or processor.