1. Coincident Source receiver Concepts
Environmental and Exploration Geophysics II
Coincident Source receiver Concepts
Extracting Velocities from Seismic Data
tom.h.wilson
Department of Geology and Geography
West Virginia University
Morgantown, WV
Tom Wilson, Department of Geology and Geography

2. Common Midpoint (CMP) gather, also often referred to as Common Depth Point (CDP)
Tom Wilson, Department of Geology and Geography

3. Common Midpoint Gather
Doug Smith’s seismic Data Processing site
Tom Wilson, Department of Geology and Geography

4. Moveout and the moveout correction
Tom Wilson, Department of Geology and Geography

5. Redefine the reflection time equal to the 0-offset arrival time (t0) plus the t (drop from t0 or “moveout”).
Tom Wilson, Department of Geology and Geography

6. Assume t2 is small relative to other terms and can be ignored to approximate the moveout
t is the normal moveout correction
Tom Wilson, Department of Geology and Geography

7. Square both sides of this equation
Look at the reflection time distance relationship in terms of t2 versus x2
Square both sides of this equation
Tom Wilson, Department of Geology and Geography

8. The hyperbola becomes a straight line
Tom Wilson, Department of Geology and Geography

9. In the t2-x2 form, the slope is 1/V2
Tom Wilson, Department of Geology and Geography

10. The moveout velocity
V is derived from the slope of the reflection event as portrayed in the t2-x2 plot. The derived velocity is referred to as the Normal Moveout Velocity, NMO velocity, or, just VNMO.
Tom Wilson, Department of Geology and Geography

11. The VNMO is used as a correction velocity
If the velocity is accurately determined the corrected time  equals t0
Tom Wilson, Department of Geology and Geography

12. Fun with hyperbolas and ellipses
Tom Wilson, Department of Geology and Geography

13. If the correction velocity (VNMO) is too high then the correction is too small and we still have a hyperbola
Tom Wilson, Department of Geology and Geography

14. And we have
Tom Wilson, Department of Geology and Geography

15. Velocity Analysis
Tom Wilson, Department of Geology and Geography

16. Discussion of problems 4.1
Read over and think about how you are going to solve problems 4.5 and 4.8
Tom Wilson, Department of Geology and Geography

17. Dix Interval Velocities
The Dix interval velocity assumes VNMO velocities are equivalent to RMS velocities. Starting with the basic definition of the RMS velocity we derive the interval velocity Vn.
Read over discussions of Dix Interval Velocities (pages )
Tom Wilson, Department of Geology and Geography

18. Using Fault Polygons General Steps
Create a fault polygon set: usually identified by horizon
Digitize your fault polygon, double click and assign a fault to it
Digitize fault polygons for all faults intersecting that surface and assign the appropriate fault to each polygon
Under Fault Polygon Management Specify “Fill Color Based on Associated Fault Surface”
Go to next horizon
Tom Wilson, Department of Geology and Geography

19. See revisions (on line) to Parts 3 and 4 of the 3D seismic Interpretation procedural notes
Tom Wilson, Department of Geology and Geography

20. Horizon > Polygon Smooth
Another useful tool – smoothing can help fill gaps in your interpretations
Tom Wilson, Department of Geology and Geography

21. Some structural views and potential traps should be emerging in your interpretations
Tom Wilson, Department of Geology and Geography

22. Digitize additional horizons
To Do List
Work problem 4.1 (Bring questions in Monday). 4.1 is due next Wednesday.
Digitize additional horizons
Discuss divisions of labor with your team mates
Read over discussions of Dix Interval Velocities (pages )
Tom Wilson, Department of Geology and Geography