VSP

Question 1

What is a VSP ?

Answer 1

VSP is both a log and seismic image tool

the geophone is lowered into the borehole and then raised up gradually

Question 2

Why are VSPs useful ?

Answer 2

• VSPs are useful because they provide in situ rock properties in depth (seismic velocity, impedance, anisotropy and attentuation)
• assist in understanding seismic wave propogation (source signature, multiples and conversions)

You match the VSP with surface seismic to identify multiples in surface seismic data.

Question 3

What are the components of VSPs? (4)

Answer 3

1- seismic source array
2- wireline
3- downhold receiver array
4- recording/wireline truck

Question 4

Types of VSPs (5)

Answer 4

List and Draw
1- Zero-offset VSP 
2- walkaway VSP 
3- multi-offset VSP
4- multi-azimuth VSP
5- cross-well VSP
6- 3D VSPs

Question 5

Zero Offset VSP

Answer 5

single source position used within several tens of metres of the borehole.
1- provide seismic time-to-depth relationship
2- interval velocities in depth,
3- normal incidence

Question 6

walkaway VSP

Answer 6

several regularly offset sources from the well head.
1- determine AVO behaviour
2- create 2D reflectivity image

Question 7

multi-offset VSP

Answer 7

several sources at various offsets

Question 8

multi-azimuth VSP

Answer 8

several sources in different directions

Question 9

cross-well VSP

Answer 9

need 2 adjacent wells

Question 10

Composite plot

Answer 10

• well logs (sonic and gamma log in depth)
• synthetic seismograms
• VSP data (in TWT on teh vertical axis. Offset VSP yields an offset image both for P waves and converted PS waves
• surface seismic(VSP images can be correlated and integrated into the interpretation).

Question 11

3D VSP

Answer 11

full areal set of shots on the surface.

can be shot in conjunction with 3D surface seismic survey

Question 12

Objective using 3D VSP

Answer 12

make a full 3D image of the subsurface using VSP and surface seismic

Question 13

downgoing

Answer 13

last leg of travel path is “down” toward the geophone

Question 14

upgoing

Answer 14

last leg of travel path is “up” toward the grophone

Question 15

VSP Processing Steps

Answer 15

Deconvolution
Stack
Filter
Scale