1. Seismic Methods Geoph 465/565 Vertical Seismic Profiling– Nov 2, 2015
Lee M. Liberty
Research Professor
Boise State University

2. ERB borehole seismic vertical component
44 m / ms = 1,892 m/s

3. Seismic Methods – body waves
Surface refraction
Surface reflection
VSP
Cross well

4. VSP Uses Direct tie of seismic to well logs
Better signal/noise than seismic
Image below the bit
Higher resolution view than seismic
Image laterally away from the well
Distinguish primaries from multiples
High resolution mini seismic surveys

5. VSP ray geometries

6. Vertical Seismic Profiling (VSP) Example
VSP data showing a strong reflector “A” at a depth of about 9850 ft (after Hardage, 1997).

7. VSP and sonic logs

8. Why differences between well log synthetics and seismic data
Logs record frequencies in kilohertz, seismic usually <100 Hz
Logs only measure several feet around well bore
Synthetics do not include attenuation, dispersion, multiples, etc.
Synthetics assume 1-D (Zero-offset) response
Seismic data includes range dependent effects (AVO)
Sonic and density logs can be inaccurate
poor hole conditions such as washouts
Recording or editing problems or errors
Why VSPs usually have better match with seismic
VSP frequencies similar to seismic data (~5-100 Hz)
Measures larger area around well bore (10s to 100 feet)
VSPs include attenuation, dispersion, multiples, etc. like seismic
Zero-offset VSP in straight hole produces 1-D response – unlike seismic data with multiple offsets
Offset VSPs include range dependent effects (AVO)

9. Ambient noise with depth

10. VSP reflections
Downgoing
Upgoing

11. VSPs Processing First arrival times: - to flatten downgoing
+ to flatten upgoing and convert to two-way time

12. Mean and Median Mix (Trace mix, Median Filter)
How to do a mix (running average):
For each sample interval, an average of n traces is taken, where n is the mix window length. The average replaces the value of the center trace of the window. The window is moved one trace to the right and the procedure repeated
The median mix rejects noise spikes and data not horizontally aligned
Seismic unix  sumix

13. Mean and Median Mix Consider a step function
Mean values smears changes laterally
Median filter preserves changes and eliminates inconsistent data
Mean
Mix
Median
Mix

14. VSP Processing
Hinds, et al., 1996
Seismic Unix  sumedian

15. Corridor Stack
Stack of selected VSP traces closest to the well bore (yellow)
Where the geophone is closest to the reflector and least contaminated by multiples

16. VSP Downgoing Upgoing Corridor stack Interval velocities
Tie to lithologic logs

17. Downgoing
Upgoing
Corridor stack
Interval velocities
Tie to lithologic logs

18. Attenuation analysis

19. VSP Downgoing Upgoing Corridor stack Interval velocities
Tie to lithologic logs

20. Corridor stack

21. Zero Offset VSP Imaging
Steeper the dip, the farther updip the imaging
Cannot tell updip direction from a zero offset VSP

22. VSP Imaging Can’t always get what you want.
Hard to image down dip
Can’t always get what you want.
Need to plan ahead using modeling
Hardage, 1983

23. Walkaway VSP Mini seismic survey. Can also do in 3-D
Produces multi-fold data (CMPs)

24. Walkaway VSP
Walkaway VSP at a range of geophone depths for both horizontal (S1 and S2) and vertical (V) receivers.
The horizontal energy decreases in amplitude (relative to the vertical component) with depth, related to converted wave partitioning at greater raypath angles (bottom)
Static effects from the walkaway survey showing two-way travel time delay times from a range of receiver depths. These data were calculated by subtracting the average direct wave velocity calculated at each receiver depth.

25. ERB borehole seismic vertical component
44 m / ms = 1,892 m/s

26. ERB borehole seismic horizontal components
north
east

27. WELL CONSTRUCTION: The well casing shall be 4” diameter PVC (ASTM Schedule 40) internally threaded to allow the use of geophysical equipment. Surround the PVC with 6” steel casing (ASTM Schedule 40) with a nominal wall thickness of inches that extends from the bottom of an aluminum flush mounted termination box to a depth of 20 feet below the finished first floor slab. SLOTTED SCREEN: Provide 0.30 slot screen beginning at 50 feet below the first floor finish to a depth of 118 feet (36 m). The well driller will not install well screens, perforated casing or filter pack across a confining layer(s) separating aquifers of different pressure, temperature, or quality.