Unclos Tutorial M. Depth conversion

In order to use the sediment formulae criterion in UNCLOS Article 76, we need a data set containing the sediment thickness. This data set can be based on seismic data. This tutorial has some exercises which cover the basics for working with seismic data. Aim of this tutorial

1. Generate sediment thickness profile from seismic interpretation using a velocity table

2. Import a velocity data set

3. Convert Interval velocities from Stacking velocities or RMS velocities

4. Generate sediment thickness profile from seismic interpretation using interval velocity data set

Exercise: Generate Sediment Profile using a velocity look-up table Use seismic interpretation of the seabed and the sediment base combined with interval velocity table to generate a sediment profile.

The seismic line interpreted in the previous Tutorial is stored with milliseconds as a z coordinate, not meters. In order to compute a sediment thickness in meters, we need to do a depth conversion.

In order to generate the sediment thickness, we need at least an interpretation of the sediment base, and the seabed surface. Geocap can also use more interpreted horizons if you provide them. You will then need to add velocities to these horizons as well. The interval velocity used at a horizon should be the interval velocity in the interval between the horizon and the horizon above.

• Locate the folder “3. Sediment Data / Velocities / Velocity Profiles”
• Right click the folder and select the command object “Generate Velocity Profile”
• Browse in the Seismic line, and the interpretation folder in the Input data group box.
• Select “Use interval velocities from: table"
• Type in horizon name “Seabed Surface” and Interval velocity “1500”, and click add
• Type in horizon name “Sediment Base” and the interval velocity “2100”, and click add

It is important that the horizon names match exactly the names you used when interpreting the seismic lines. The velocities are the interval velocity to use in the interval above the specified horizon. In this case we use 1500 meter/second for the velocity in water, and 2100 meter/second for the interval velocity in the sediments. It is also possible to use a velocity function. This is however not covered in this exercise.

• Click “Execute”

If you select folders containing the seismic lines as input instead of single data sets, Geocap will try to generate more velocity profiles in one go. A dialog with a list of the matching seismic lines will appear.

• Click Ok, and the velocity profiles will be generated in the “Velocity Profiles” folder
• Click close in order to close the “Generate velocity profile” dialog
• Right click the new velocity profile and select “map” in order to see the profile

The velocity profile holds all the data necessary to do generate a sediment thickness. It holds both the interpretations in time, and the interval velocities to use in the interval between the interpretations.

• In order to generate a sediment thickness profile, right click the velocity profile, and select “Calculate Sediment thickness”

A new data set will be created in “3. Sediment Data/ Sediment profiles”

• Right click the new data set, and select table view.

The “Table view dialog” of the data set will appear. The x,y and z is the position and the sea depth at that point. The S value is the sediment thickness. The Shot point column is the points corresponding shot point from the seismic line.

• Click close in order to close the dialog.
• Right click the data set again, and select “display profile as cross section”

A sediment profile should now be displayed, you may need to un-toggle the Velocity display and the seismic display, if you are still displaying them in order to get a good view of it.

Exercise: Import a velocity data set Import a velocity data set from an ASCII column file.

Velocities are usually provided as ASCII column files. The file should contain the shot point, time, and velocity. The file may also contain coordinates. In our training data set, these are not provided so we will have Geocap assign navigation from a navigation data set. If the file contains velocities from more than one line, it should also have a column with the line name.

• Locate the folder “3. Sediment Data / Velocities / Stacking Velocities”
• Right click the folder and select the command object “Import ->Stacking Velocities (no navigation)"
• Browse in the data set called ATL-LOS-00.vel
• Adjust the columns according to the following screen shot, and click execute

The data set has now been imported into your project. However it still does not hold any coordinates. In order to visualize the stacking velocities with the seismic data, we need to assign navigation to the velocities. Geocap will use the shot point number in the velocity data set and match them with the shot points in a navigation file. Either a separate navigation file, or the actual seismic line can be used as source of navigation. Geocap will match the shot points in the navigation file with the shot points in the velocity file.

• Right click one of the velocity data sets, and select the command object "Assign Navigation"
• Browse to "3. Sediment Data /Seismic Lines" and highlight the corresponding seismic line
• click ok
• Right click the velocity data set again, and click "Map Data"

A color map of the velocity data should appear. If you display the seismic line at the same time, you should be able to see that the velocities match the seismic line.

The velocity data sets should have the exact same name as the seismic line. If this is the case, then you can use the assign navigation command object on the folder containing the velocity data. You should then browse in the folder containing the navigation. Geocap will match the data sets by their name, and assign navigation accordingly. This way you do not need to assign navigation to one and one data set, but can do them all in one go.

Exercise: Convert Stacking velocities or RMS velocities to Interval velocities

If you have imported stacking velocities or RMS velocities, we need to convert them to interval velocities before we can use them as input to the "Generate Velocity Profile" command object.

• Locate the folder “3. Sediment Data / Velocities / Stacking Velocities”
• Right click the folder and select the command object “Compute Interval Velocities (Dix Formula)"

The result will be stored in the folder "3. Sediment Data / Velocities / Interval Velocities"

Dix formula will produce interval velocities if it is run on RMS velocities. You may also use this formula on stacking velocities, and thereby use the stacking velocities as an approximation for RMS velocities.

Exercise: Generate sediment thickness profile from seismic interpretation using interval velocity data set Use seismic interpretation of the seabed and the sediment base combined with interval velocity data set to generate a sediment profile.

This exercise is quite similar to the first exercise in this tutorial. The only difference is that we will base the velocities on a data set in the project instead of a look-up table

In order to generate the sediment thickness, we need at least an interpretation of the sediment base, and the seabed surface. Geocap can also use more interpreted horizons if you provide them.

• Locate the folder “3. Sediment Data / Velocities / Velocity Profiles”
• Right click the folder and select the command object “Generate Velocity Profile”
• Browse in the Seismic line, and the interpretation folder in the Input data group box.
• Select “Use interval velocities from: Data set in Project"
• Browse in the Interval velocity input data group box.

It is important that the Interval velocity data set has the same name as the corresponding seismic line. It is also important that the shot point numbering in the velocity file correspond to the shot point numbering of the seismic line.

• Click “Execute”

If you select folders containing the seismic lines and the velocity data as input instead of the data sets, Geocap will match the names, and try to generate more velocity profiles in one go. A dialog with a list of the matching seismic lines will appear.

• Click Ok, and the velocity profiles will be generated in the “Velocity Profiles” folder
• Click close in order to close the “Generate velocity profile” dialog
• Right click the new velocity profile and select “map” in order to see the profile

The rest of this exercise is similar to the end of the first exercise in this Tutorial. The velocity profile holds all the data necessary to generate a sediment thickness. It holds both the interpretations in time, and the interval velocities to use in the interval between the interpretations.

• In order to generate a sediment thickness profile, right click the velocity profile, and select “Calculate Sediment thickness”

A new data set will be created in “3. Sediment Data/ Sediment profiles”

• Right click the new data set, and select table view.

The “Table view dialog” of the data set will appear. The x,y and z is the position and the sea depth at that point. The S value is the sediment thickness. The Shot point column is the points corresponding shot point from the seismic line.

• Click close in order to close the dialog.
• Right click the data set again, and select “display profile as cross section”

A sediment profile should now be displayed, you may need to un-toggle the Velocity display and the seismic display, if you are still displaying them in order to get a good view of it.