Synopsis

Question 1

Causes of seismic noise

Answer 1

Random Noise:
• Wind - notably in desert & near trees
• Industry
• Roads, trains (also
electrical pick-up)
• Surf zone - coastal areas
• High tension power lines & plants
• Nightlife

Organised Noise:

• Groundroll
• Near surface
scattering
• Shallowrefractions
• Shallow reverberations

Question 2

2 D over 3 D Survey

Answer 2

2D
• Cheap
• Simpleoperation
• Straight processing
• Seriousimaging/ subsurface positioning problems

3D
• Not so cheap
• Possiblycomplex
operation
• Straight processing possible, yet often complicated processing is needed
• Considerably less imaging problems

Question 3

Fundamental criteria & requirements of the survey

Answer 3

• Desired spatial resolution
• Subsurface geometry & depth of objective(s)
• Envisaged processing sequence, AVO, inversion etc
• Choice of acquisition geometry
• Environmental & logistical issues

!!!!Depth and nature of objective(s) determines acquisition geometry !!!!!!

Question 4

5 major Phases - classical séquences

Answer 4

1. Pre-processing1. Merge of field tapes with obs. logs, topo, bad trace editing
2. Pre-stack processing2. Statics, deconvolution, velocity derivation and application
3. Post-stack processing3. NMO correction, stacking and deconvolution
4. Imaging (Migration)4. Imaging and bandpass filtering
5. Archiving
6. Tape & report generation

Question 5

How to –> eliminate unwanted signal

Answer 5

Filtering-k/f

Bandpass

Question 6

How to suppress random noise

Answer 6

stacking

Question 7

How to focus and position better the seismic image

Answer 7

Imaging and migration

Question 8

CMP vs CDP

Answer 8

CMP = smear
loss of resolution
improper position

CDP = better to image before stacking !

Question 9

Time domaine VS Depth domain

Answer 9

T-domaine =

• Straightforward from recorded traces
• Relative simple operators
• One-pass operations

Depth-domaine =
• Depth model needed
• No straightforward operators
• Layer-by layer approach

Question 10

Post stack vs Prestack

Answer 10

Post =
Fast and Cheap
One-pass operation
Error prone

Prestack =
Expensive & time consuming
Iterative opé (répétitif)
Best available



Question 11

Minimum and Zero Phase wavelet

Answer 11

Minimum Phase Wavelet:
a) Physically realizable
b) Highly asymmetric
c) Very difficult to pick when dealing with low frequencies and low amplitudes
d) All the energy is “front-loaded”, and the time-lag between “zero-time” and the peak of the main
pulse is not constant

Zero Phase Wavelet: The only meaningful signal

a) Unphysical
b) It peaks at time=0
c) Its peak representative for reflection coefficient
d) It is easier to interpret as the reflection time is exactly at the peak of the main amplitude.
e) The wider the frequency band, the sharper the signal