FIG. V-10. Vertical seismic profile
) Each trace is recorded at a depth in a borehole using an air-gun source at the surface. (b
) Same except each trace has been shifted by the one-way traveltime to the surface, thus aligning reflections (upcoming events) horizontally. A shift in the other direction would align downgoing events horizontally. (c
) Portion of a reflection record section across the well location. (d) Sonic log in the well
Measurements of the response of a geophone at various depths in a borehole to sources on the surface. See Figures V-10, V-11, and Sheriff and Geldart.
Sometimes the surface sources are moved about the area as well as the geophone depth being changed. Where the source point is an appreciable horizontal distance from the well head, the result is an offset VSP; this provides a way to look to the side of the borehole.
For an azimuthal VSP sources are offset in different directions. In a walkaway VSP a surface source moves while the geophone in the borehole remains stationary; this provides another way to look to the side of the borehole. In a reversed VSP the source is in the borehole and geophones are on the surface.
VSPs are also run in directional and horizontal wells. A walkabove VSP is made with the sonde in a deviated hole and the source moved so as to be vertically above it.
The result of a VSP is often displayed as a corridor stack; see Figure C-16.
FIG. V-11. Vertical seismic profile
FIG. C-16. Corridor stack
. ‘‘Corridor stack’’ means the outer corridor unless ‘‘inner’’ precedes it. (1) Median-filtered VSP; (2) inside corridor; (3) inside-corridor stack; (4) outside-corridor stack; (5) outside corridor (reversed in direction)
- ↑ 1.0 1.1 Sheriff, R. E; Geldart, L. P (August 1995). Exploration Seismology, 2nd Ed. Cambridge Univ. Press. p. 490. ISBN 9780521468268. Cite error: Invalid
<ref> tag; name "Sheriff" defined multiple times with different content
- ↑ Gilpatrick, Rory; Fouquet, Doyle (1989). "A user’s guide to conventional VSP acquisition". The Leading Edge 8 (3): 34–39. doi:10.1190/1.1439615. ISSN 1070-485X.
- ↑ Hinds, Ronald C.; Anderson, Neil L.; Kuzmiski, Richard D. (1996). VSP Interpretive Processing. Society of Exploration Geophysicists. doi:10.1190/1.9781560801894.
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