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Elastic Impedance Inversion in HRS-9

Date: December 28, 2012Susan 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. Create several elastic impedance logs at different angle ranges. B. Create elastic impedance earth models from these logs.C. Invert these models to create E.I. volumes for the angle ranges.D. Cross plot the E.I. volumes against each other to define zones of AVO anomalies.E. Investigate these anomalous zones to see if they are potential prospects.

For this example, we will use only two angle ranges: Near and Far.

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Create EI Logs in HRS-9: Near Log

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1. Select Log Processing> Log Transform>Impedances> Elastic P-Impedance to bring up the Process Parameters Page.

Process Parameters Page, Near Log

2. Create an EI_Near log at 7.5°.

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The EI_Near Log

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Create an EI_Far Log

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3. Select Log Processing>Log Transform>Impedances> Elastic P-Impedance.

Process Parameters Page, Far Log

4. Create a EI_Far log at 22.5°.

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The EI_Far Log

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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.

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Cross Plot the Logs

7. Cross plot the two EI_Nearand EI_Far logs. This will show whether these angle ranges can distinguish zones of interest.

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Cross Plot EI_Near versus EI_Far

Because we can see different trends and because the lower trend may indicate prospects, we will continue the process. 11

Notice the normal AVO trend

And this separate trend, which defines zones of interest

Modify the Cross PlotChange the annotation of the X/Y axis and the name of the Cross Plot:

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8. Double click the names and modify these names.

Find the Zone of Interest

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We will now mark the two AVO trends, starting with the normal trend.

9. Click the Polygonicon. 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.

Create the first zone (Zone1)

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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.

Create the second zone (Zone2)

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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.

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.

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Create Range Stack Volumes: Near Stack

14. Create the near angle stack volume, labeled “7.5°” (the angle half-way along that angle range).17

a. Select Process>Seismic Processing>Stack>Angle Stack.

b. Set the stack parameters.

c. Click Specify Velocity.

d. Set up the Velocity Field Parameters.

e. Click OK.

The midpoint is 7.5

The Angle Stack at 7.5°

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The volume we used The resulting stack

Create an Angle Stack at 22.5°

15. Create the Far angle stack volume, labeled 22.5° (the angle halfway between 15 and 30 °).19

The midpoint is 22.5

The Angle Stack at 22.5°

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The volume we used The resulting stack

Near and Far Angle Stacked Volumes

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Near Far

Create a Model on the Near Angle, Part 1

16. Create a model on the near angle stacked volume (7.5°). 22

a. Select Processes> Strata Model>Build Strata Model.

b. Supply a new name for the model.

c. Select the well and horizons.

d. Click Show Advanced Options.

Create a Model on the Near Angle, Part 2

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e. Click the Next button

f. Select Typical setup for Elastic Impedance Inversion.

g. Click the Nextbutton.

Create a Model on the Near Angle, Part 3

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h. Select the well for model building

i. Click Next. j. Check the Geometry and then click Next.

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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.

Create a Model on the Near Angle, Part 4

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n. Select the horizons for model building, then click Next.

m. Select the Domain, then click Next.

Create a Model on the Near Angle, Part 5

The Near Angle Stacked Model, Part 6

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Model Based Inversion, Part 1

17. Perform a model-based inversion.28

a. Select Processes>Inversion> Process>Post-stack Inversion.

b. Define the inversion parameters.

Model Based Inversion, Part 2

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c. Give a new output name

The Near Angle Inverted Result

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Create a Far Angle Model, Part 1

18. Build a model on the far angle stacked volume (22.5°)31

a. Select Processes> Strata Model> Build Strata Model.

b. Give a new name to the model.

c. Select the well and horizons.

d. Click Show Advanced Options.

Far Angle Model, Part 2

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e. Click Next.

f. Select Typical setup for Elastic Impedance Inversion.

g. Click Next.

Far Angle Model, Part 3

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h. Select the well for model building.

i. Click Next.j. Check the Geometry and then click Next.

Far Angle Model, Part 4

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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.

Far Angle Model, Part 5

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m. Select the Domain, then click Next.

n. Select the horizons for model building, then click Next.

Far Angle Model, Part 6

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Far Angle Model Based Inversion, Part 1

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a. Select Processes>Inversion> Process>Post-stack Inversion.

19. Perform a model-based inversion for the far angle volume.

b. Define the inversion parameters.

Far Angle Model Based Inversion, Part 2

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c. Give a new output name

Inverted Result of Far Angle Volume

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Near and Far Inversion Results

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Cross Plot of Near and Far

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a. Select Processes>Cross Plotting>Cross Plot Seismic.

20. Cross plot the near and far inversion results.

Cross Plot of Near and Far

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Select the Zone Set

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21. Select the zone set EI_Near-vs-EI_Far created on pages 13 and 14.

The Zones on the Cross Plot

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This zone is what we are interested in.

The Zone Displayed on a Section

The zone of interest is colored blue. 45