Seismic data processing 12
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This document discusses velocity analysis techniques for seismic data processing. It introduces normal moveout (NMO) correction, where the proper velocity must be chosen to horizontally align reflections. The velocity spectrum method is described, which applies hyperbolic transformations and weighted stacking to plot coherence across a range of velocities. This velocity spectrum helps identify the correct velocities to use for NMO correction and horizontally aligning reflections in common midpoint gathers. Deeper reflections generally have higher velocities due to increasing pressure and temperature with depth in the Earth.
Seismic data processing 12
- 1. Seismic Data Processing Lecture 12 Velocity Analysis Dr Amin Khalil School of Physics, USM
- 2. Introduction: In NMO correction we realized that we must input velocity (RMS velocity) in order to correct for normal moveout. The choice of proper velocity is crucial as if the velocity is either too large or too small the traces will not align.
- 4. In NMO correction our goal is that all reflections must horizontally aligned.
- 5. We apply CMP velocity pannel, from this pannel we select the velocity (rms) that result in horizontal align of each reflector. We use iterative scheme to obtain the best velocity value for each reflector.
- 6. Deeper reflector usually have higher velocity. Why?!!!
- 10. Description of velocity spectrum method: Velocity spectrum is hyperbolic transformation that can be applied through the folowing steps: 1- correct the CMP gather for arbitrary stacking velocity. 2- Apply weighted stacking to measure coherency. Stacking will with one trace. 3-repeat for next velocity. 4-For a complete set of velocities we plot the results. This is called velocity spectrum.
- 11. Example for velocity spectrum method: Starting from the synthetic CMP of the form
- 12. Example continued For this CMP we apply the semblance for velocities ranging from 1000 m/s to 3000 m/s with velocity step of 50 m/s The semblance is defined using the relation Which is often simplified to: For fewer sample points (2p) of the time window or gate.
- 13. Output:
- 15. Factors controlling seismic Velocity
- 21. Seismic velocities of common rock types
- 22. Thank you