Time to Depth Conversion and Velocity Modeling
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Time to Depth Conversion and Velocity Modeling Course
Introduction:
Seismic data is acquired in time - the time is 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.
In the last decade or two, large strides have been made in seismic processing, especially in PreStack Depth Migration. Routinely used advanced migration algorithms now require more accurate velocity models. Better tools have been developed to ascertain the velocity, and more time and effort are now spent in velocity analysis by the seismic processors. This has greatly improved current velocity models. The interpreter, however, still needs to know how the models are made, how to quality control them, and how to modify and correct them when needed.
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
Who Should Attend?
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.
Course Outlines:
- 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