Page 48 - Hydrocarbon

Exploration 35

a. vertical seismic profiling (VSP) with source at surface and receivers
lowered down borehole.
well 1 well 2
direct
S wave at t 1

R-t
1
reflected
wave at t 1

R-t 2
direct S = source
wave at t R = receiver
2
reflected
wave at t
2
b. cross-hole seismic surveying
well 1 well 2

direct wave at t 1

S-t 1 R-t 1
reflected wave at t 1

S-t R-t
2 2

S-t 3 R-t 3

S-t 4 R-t 4

Figure 3.17 Principles of borehole seismic surveying.

resembles a spike (Figure 3.18). In effect deconvolution tries to remove the effects of
the earth’s filter by reproducing the geological boundaries as a reflectivity series.

3.2.2.5.3. Velocity analysis and NMO correction. From previous sections it has
become clear that seismic velocity plays an important role in seismic surveying and
processing. It is the one parameter that allows the seismic image to be converted
into a geological depth section. There are several types of seismic velocity, such as