Geop 397 - Fault Shadow

Question 1

Specify 3 reasons for appearance of false structures on seismic sections

Answer 1

• regional or local velocity changes
• acquisition footprint - changes in fold and layout pattern
• processing artifacts -
  eg migration “smiles” where bad traces are visible
  eg “over migration:

Question 2

what is the consequence of basing drilling decisions on false structures?

Answer 2

non-commercial well or dry hole

Question 3

what are the 2 names given to velocity generated false structures

Answer 3

velocity sag

pull up

Question 4

What 2 false structures do velocity sag and pull-up create ?

Answer 4

velocity sag creates false syncline

pull up creates false rollover

Question 5

What is a possible reason for the velocity affect in creating a false structure?

Answer 5

Juxtapositiion of a high velocity zone in the footwall against lower velocity zone in the hanging wall

Question 6

What other effect is caused by velocity variations?

Answer 6

disruption in the continuity of the reflectors

Question 7

What is the possible solution to the fault shadow problem?

Answer 7

Pre-stack depth migration