Elastic Impedance Inversion
in HRS-9
Date: December 28, 2012
Susan Li, David Worsick
Elastic Impedance Inversion
Elastic impedance volumes created at different angle ranges can be used in cross
plots to highlight AVO anomalies. This process requires well log data.
The process is:
A.
B.
C.
D.
E.
Create several elastic impedance logs at different angle ranges.
Create elastic impedance earth models from these logs.
Invert these models to create E.I. volumes for the angle ranges.
Cross plot the E.I. volumes against each other to define zones of AVO anomalies.
Investigate these anomalous zones to see if they are potential prospects.
For this example, we will use only two angle ranges: Near and Far.
2
Create EI Logs in HRS-9: Near Log
1. Select Log Processing>
Log Transform>Impedances> Elastic P-Impedance to
bring up the Process Parameters Page.
3
Process Parameters Page, Near Log
2. Create an EI_Near log at 7.5°.
4
The EI_Near Log
5
Create an EI_Far Log
3. Select Log Processing>
Log Transform>Impedances> Elastic P-Impedance.
6
Process Parameters Page, Far Log
4. Create a EI_Far log at
22.5°.
7
The EI_Far Log
8
Display EI_Near and EI_Far Logs Together
Display the EI_Near and
EI_Far logs on same track:
5. Click the Eye button to
bring up the Layout dialog.
6. Select EI_Near and
EI_Far on the same track.
Notice that the EI_Far log
plots to the left of the
EI_Near log in the gas zone
and to the right of the
EI_Near log in the rest of
the log.
This change in behavior will
differentiate zones of AVO
anomalies.
9
Cross Plot the Logs
7. Cross plot the two EI_Near
and EI_Far logs.
This will show whether these
angle ranges can distinguish
zones of interest.
10
Cross Plot EI_Near versus EI_Far
Notice the normal AVO trend
And this separate trend, which defines
zones of interest
Because we can see different trends and because the lower trend may
indicate prospects, we will continue the process.
11
Modify the Cross Plot
Change the annotation of
the X/Y axis and the name
of the Cross Plot:
8. Double click the
names and modify
these names.
12
Find the Zone of Interest
We will now mark the
two AVO trends, starting
with the normal trend.
9. Click the Polygon
icon. The default names
for the Zone Set and the
Zone will be displayed.
You can highlight the
names of the Zone Set
and the Zones to
change them.
13
Create the first zone (Zone1)
10. Draw a polygon
over the upper points
trend (the normal AVO
trend) using the mouse,
then double-click to
finish this polygon.
Note that we define this
zone to use color to
emphasize the
difference between
zones. We can skip this
step and only define the
anomalous zone with
color.
14
Create the second zone (Zone2)
11. Click the Polygon
icon again. The default
name for the second
zone will be Zone2.
This shows an AVO
anomaly and is
therefore a zone of
interest for exploration.
We must define this
zone.
12. Draw a polygon for
the Zone Of Interest
and double-click to
finish.
15
The Cross Section
13. Select Options>Cross Section to show the cross section. This shows the
normal AVO effect in red and the anomaly in blue.
16
Create Range Stack Volumes: Near
Stack
d. Set up the Velocity
Field Parameters.
The midpoint is 7.5
a. Select
Process>Seismic
Processing>Stack
>Angle Stack.
b. Set the
stack
parameters.
c. Click Specify
Velocity.
e. Click OK.
14. Create the near angle stack volume, labeled “7.5°” (the angle half-way along that angle range).
17
The Angle Stack at 7.5°
The volume we used
The resulting stack
18
Create an Angle Stack at 22.5°
The midpoint is 22.5
15. Create the Far angle stack volume, labeled 22.5° (the angle halfway between 15 and 30 °).
19
The Angle Stack at 22.5°
The volume we used
The resulting stack
20
Near and Far Angle Stacked Volumes
Near
Far
21
Create a Model on the Near Angle,
Part 1
b. Supply a new name for the model.
a. Select Processes>
Strata Model>Build
Strata Model.
c. Select the well and horizons.
d. Click Show
Advanced Options.
16. Create a model on the near angle stacked volume (7.5°).
22
Create a Model on the Near Angle,
Part 2
f. Select Typical
setup for Elastic
Impedance
Inversion.
e. Click the Next button
g. Click the Next
button.
23
Create a Model on the Near Angle,
Part 3
h. Select
the well for
model
building
i. Click Next.
j. Check the Geometry and
then click Next.
24
Create a Model on the Near Angle,
Part 4
k. Select the
logs and then
click Next.
l. From the pull-down menu,
choose EI_Near log for the
Elastic Impedance, then click
Next.
25
Create a Model on the Near Angle,
Part 5
n. Select the
horizons for
model building,
then click Next.
m. Select the Domain, then click
Next.
26
The Near Angle Stacked Model,
Part 6
27
Model Based Inversion, Part 1
a. Select
Processes>Inversion>
Process>Post-stack
Inversion.
17. Perform a model-based inversion.
b. Define the
inversion parameters.
28
Model Based Inversion, Part 2
c. Give a new output name
29
The Near Angle Inverted Result
30
Create a Far Angle Model,
Part 1
b. Give a new name to the model.
a. Select Processes>
Strata Model> Build
Strata Model.
c. Select the well and horizons.
d. Click Show
Advanced Options.
18. Build a model on the far angle stacked volume (22.5°)
31
Far Angle Model, Part 2
f. Select Typical
setup for Elastic
Impedance
Inversion.
e. Click Next.
g. Click Next.
32
Far Angle Model, Part 3
h. Select the
well for model
building.
i. Click Next.
j. Check the Geometry and
then click Next.
33
Far Angle Model, Part 4
k. Select the
logs and click
Next.
l. From the pull-down menu,
select the EI_Far log for the
Elastic Impedance, then click
Next.
34
Far Angle Model, Part 5
n. Select the
horizons for
model building,
then click Next.
m. Select the Domain, then click
Next.
35
Far Angle Model, Part 6
36
Far Angle Model Based Inversion,
Part 1
a. Select
Processes>Inversion>
Process>Post-stack
Inversion.
b. Define the
inversion parameters.
19. Perform a model-based inversion for the far angle volume.
37
Far Angle Model Based Inversion,
Part 2
c. Give a new output name
38
Inverted Result of Far Angle Volume
39
Near and Far Inversion Results
40
Cross Plot of Near and Far
a. Select
Processes>Cross
Plotting>Cross Plot
Seismic.
20. Cross plot the near and far inversion results.
41
Cross Plot of Near and Far
42
Select the Zone Set
21. Select the zone set EI_Near-vs-EI_Far created on pages 13 and
14.
43
The Zones on the Cross Plot
This zone is what
we are interested
in.
44
The Zone Displayed on a Section
The zone of interest is colored blue.
45