F. Seismic Display and Interpretation

Owned by Erlend Kvinnesland
Last updated: Sept 23, 2013
6 min read

Introduction

The vast amount of seismic display commands and color tables, together with the flexibility of the graphical window makes Geocap a great tool for visualizing seismic.

Seismic interpretation is primarily meant for interpreting 2D sections. It has the basic functionality like auto tracking and manual interpretation. It is a simple and direct interpretation system which is suited for cases where one just want to interpret the major reflectors.

Exercises

Seismic Display

The main display command for seismic is Seismic Display. This command has two display options in its Edit menu; Display seismic and Display LOD seismic, which is default. Display LOD seismic is a level of detail display which increases the resolution as you zoom closer. Depending on the graphics card on your computer, this might not work. In that case, right click Seismic Display in your Toolbox, select Edit, check the Display seismic box and pressExecute.

Exercise

Display a seismic line

  1. Right click one of the seismic lines in 2. Seismic Data/Survey3 and select Zoom to Data.
  2. Right click the seismic again and select Seismic Display. (If it shows up in one single color, try the suggestion in the info box above)
  3. Try zooming in, rotate and changing the Z scale.

 

There are several ways of changing the color table on a seismic line. In the next exercise we are going to try a few of them.

Exercise

Change color table on a seismic line

  1. While having a seismic line displayed in the graphics window go to your Toolbox and click on the Color Tables tab
  2. Find a seismic color table, drag and drop it on to the seismic line. Notice that the color table changed.
  3. In the lower right corner of Geocap change the combo box to Seismic. This shows the default seismic color table.
  4. In the Toolbox right click another color table and select Activate. Notice that the default color table in the lower right corner changed.
  5. Right click the seismic line in your project and run Seismic Display again. Notice that it is using the default color table that you set.
Exercise

Adjust color table range

  1. While having a seismic line displayed in the graphics window click and notice that the cursor changes to a crosshair.
  2. Click on the seismic line in your graphics window.
  3. In the menu that pops up click and hold the button with the two arrows pointing towards each other (><). Notice how the contrast increases when reducing the map range on both ends.
  4. Try to drag the sliders individualy and notice the difference.
  5. Click OK to keep settings or Cancel to dismiss the settings

Seismic Interpretation

The seismic interpretation tool lets you interpret horizons, faults and observations. This can be done both manually and automatically. In your Geocap project you will typically have an interpretation folder with one or more Ihorizon datasets, one Faults folder and one Observations folder.

The structure of a horizon in Geocap is as follows:

  • One horizon can contain interpretation from several seismic lines
  • Each line can have many segments
  • Each segment can have many picks

This means that each horizon will normally contain thousands of picks along different seismic lines. Each pick is stored with the following information:

  • Time value
  • Seismic line name
  • Shot point

The way Geocap stores its horizon data is compatible with most other seismic interpretation systems.

In the next few exercises we are going to interpret the seabed for the three seismic lines in Survey3.

Exercise

Create a horizon

  1. Go to Tools > Seismic Interpretation
  2. Click Browse button to select the interpretation folder
  3. Select the seismic interpretation folder 3. Interpretation and click OK
  4. Click the button in order to create a new IHorizon. The IHorizon dialog will appear
  5. Type in Seabed as the name of the new horizon
  6. Click on the Graphical Settings tab
  7. Set Line Width to 5
  8. Check the User Defined Color and pick a color for the horizon.
  9. Click OK

Notice that your 3. Interpretation folder contains a Seabed dataset with the schema Ihorizon.

Exercise

Interpret a horizon

  1. Right click the Survey3 folder containing the seismic lines and select Zoom to Data
  2. Right click the folder again and select Seismic Display
  3. Make sure the Seismic Interpretation menu is open and that the Seabed horizon has been selected
  4. Click the button and click on the seismic line that you want to interpret on, in the graphical window (with your left mouse button). Notice that the line name is shown in the menu.
  5. In your project hide the two seismic lines that was not selected, by unchecking them.
  6. Make sure Snap mode is set to   
  7. Click the button and zoom into the area where you want to start the interpretation
  8. Pick points along a reflector on the seismic line by pointing the mouse cursor an pressing the <space> key or p on the keyboard. If you want to undo a pick, you can click the d key.
  9. Stop interpreting by click the button.
  10.  

    To continue the interpretation click the button and continue picking points

  11. Try to interpret over your previous interpretation and click the button. Observe that the
Exercise

Update an interpret a horizon

  1. Click the button.

  2. Try to interpret above or below your previous interpretation and then click the button. Observe that the interpretation is updated accordingly.

Exercise

Deleting parts of an interpretation

  1.  Click the button.

  2. Pick two points: the start- and the end point by pressing the <space> key. The part of the interpretation between the two points is automatically deleted

  3. Try changing the combo box to between beginning and pick
  4. Click the button
  5. Pick one point by pressing the <space> key. The part to be deleted will be highlighted.
  6. Click Yes if you want to delete the segment.
Exercise Continued

Interpreting with auto-tracking

  1. Look at the seismic display and identify the reflector representing the seabed. Compare the color of the seabed reflector with the seismic color table. The color on the left side of the color table represents minima; the color on the right represents maxima. Select Snap mode accordingly.

  2. Set Track mode to be Auto.
  3. Set Delta Z. Delta Z is the maximum allowable vertical distance between two auto-tracked points. Z is usually time in ms. A good rule of thumb is that Delta Z should be the double of the sample interval in the seismic. In our case that is 8.
  4. Click the button.
  5. Pick the horizon to autotrack by pressing the <space> or p key on the keyboard
  6. The horizon is automatically interpreted. Zoom out to see if the whole line was interpreted.
  7. If the interpretation stopped at one point press <space> or p again to continue where it stopped.
  8. When you are happy with the interpretation click the button
Exercise Continued

Interpreting with insertion (semi-auto):

  1. Keep the Snap mode to be same as you used before.
  2. Select Track mode to be Insert
  3. Set Interval to 5. This will interpret a point at every fifth trace.
  4. Click the button.
  5. Pick a start point
  6. Pick a new point a bit to the side, on the same reflector. Observe that auto tracker automatically interprets the line.
  7. When you are finished interpreting click the button.
  8. Observe that the old interpretation is updated with the new interpretation.
Exercise Continued

Complete the interpretation for the Seabed

  1. When you have completed the Seabed interpretation the for one line display one of the other Survey3 lines
  2. Click on and click on the new line with the crosshair.
  3. Continue to interpret this line using manual, auto and insert.
  4. Interpret the last line in the same way.

In your project click the triangle next to your Seabed ihorizon and observe that you now have three pick groups. One for each seismic line.