geo 395 - module 12

Question 1

true stratigraphic nature of seismic reflections

Answer 1

• acoustic impedance changes are assumed to be parallel to bedding
• no consideration to amplitude and waveshape variations

Question 2

origins of petroleum reservoirs and traps

Answer 2

• structural traps (fold - syncline, anticline) and unconformities
• stratigraphic traps (reefs and sand bodies)
• combination traps (salt domes!)

Question 3

Convolution model of seismic trace using zero phase band-pass wavelet

Answer 3

KNOW THE DIAGRAM

Question 4

Summary - How to – reflection identification

Answer 4

pick a survey by tying strong reflections on lines through wells in VSPs, synthetic seismograms or sonic logs. From velocity and density log convolved with source wavelet.

Question 5

Mis-ties and causes (in acquisition)

Answer 5

• seismic source type
• field filter
• sample rate
• field polarity
• vintge

Question 6

Mis-ties and causes (in processing)

Answer 6

• deconvolution
• statics (refraction and residual statics)
• velocities
• 2D
• vintage

Question 7

workstation interpretation - recipe

Answer 7

• collect data
• scan for QC, polarity, data structure and stratigraphy)
• tie well data
• pick horizons and faults, loops
• review start
• review struct
• map
• ID attributes (azimuth, dip, a

Question 8

3D seismic volume

Answer 8

IL, XL, X, Y, Z, time or depth
XY grid - bin size
Z increment (sample rate)
amplitude range
8 bit   -127  + 128   workstation
16 bit
32 bit

Question 9

plus and minus zero-crossings

Answer 9

Make a dot at the peaks.
left side is -ve and right side is +ve
if it looks like an S then going from -ve to +ve
If it looks like inverted S the going from +ve to -ve

Question 10

flattening - DEFINITION

Answer 10

application of a time correction to each CDP trace of a horizon such that the horizon is at a constant time

Question 11

stratigraphic interpretation

Answer 11

horizon vsp vs. synthetic

auto picking algorithm - cross correlation algorithms. compare model trace to each individual trace being tracked.

Question 12

structural interpretation

Answer 12

struct and strat interpretation needs to be done simultaneously
heave - horizontal displacement
throw - vertical displacement of 2 fault blocks

Question 13

coherency

Answer 13

generated based on similarity of adjacent traces.
high coherency if v similar
low coherence if dissimilar

Question 14

coherency coefficient

Answer 14

higher number = higher similarity