Vertical seismic profiling
|Series||Geophysical References Series|
|Title||Problems in Exploration Seismology and their Solutions|
|Author||Lloyd P. Geldart and Robert E. Sheriff|
|Pages||485 - 496|
|Store||SEG Online Store|
A source is offset 1000 m from a vertical well in which a geophone is suspended, and a horizontal reflector is present at a depth of 2000 m. Calculate the traveltimes for the reflection when the geophone is 800, 1200, and 1600 m deep if the velocity =3000 m/s
Using a coordinate system with origin at the source and the -axis positive downward, the image point (see problem 4.1) in Figure 13.4a is at (0, 4000) and the geophone coordinates are (1000, ); hence,
For 800 m depth ; for 1200 m, ; for 1600 m, .
Repeat for reflectors dipping , where the reflector intersects the well at the same point as in part (a) (see Figure 13.4b).
i) Dip down toward the well
ii) Dip down toward source
Coordinates of image are (, 4170),
Table 13.4a shows calculated traveltimes for , 1200, and 1600 m.
By how much do the values in part (a) change if the well deviates by towards the source (see Figure 13.4c)?
Well inclination changes the geophone coordiantes from (1000, ) where the in-hole depth , 1200, 1600, to where
where subscript denotes values for the deviated well. The image point remains at (0, 4000), so the traveltime is
Substituting the values of , we get the results in Table 13.4b. is the difference in traveltime from that calculated in part (a).
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|Guided (channel) waves and normal-mode propagation||Effect of velocity change on VSP traveltime|
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|3D methods||Specialized applications|
Also in this chapter
- S-wave conversion in marine surveys
- Equally inclined orthogonal geophones
- Guided (channel) waves and normal-mode propagation
- Vertical seismic profiling
- Effect of velocity change on VSP traveltime
- Mapping the vertical flank of a salt dome
- Poission’s ratio from P- and S-wave traveltimes