GIM Tracking

Tracking generation interface

The tracking generation interface in opened up from GIM > GIM Data Generation > GIM Tracking. The interface has 4 different menus and works as a wizard with next and back buttons. The 4 menus are:

1. Input
   This is where you decide which dataset to track, and which interval to use between inlines and crossline. The settings can also be adjusted so that only a subset of the cube is tracked.
2. Tracking parameters 
   This is where you set the tracking parameters to obtain best possible result.
3. Output 
   This is where you decide if you want to track both inline and crossline or just one of them. You can also change the datasets name.
4. Status
   This is where you start the generation and get an overview of how the tracking generation is progressing.

Tracking parameters

The tracking parameters menu

Tracking parameter explanations:

• Snap mode 
  Tracks min (trough), max (peak) or minmax (both). Remember that when you generate surfaces from these trackings, minmax will generate twice as many surfaces as only min or max. On regional dataset, say more than 2000 inlines/xlines, it is recommended to start with only one polarity and see how many surfaces that are generated.

• Direction
  Tracks increasing (left to right), decreasing (right to left) or both ways. When using both ways, the tracker will try to connect to where the tracker stopped when it was tracking in the first direction. 

• Gradient tracking 

• Backtrack quality control algorithm 
  When the backtrack optinon is checked the tracker will, for every pick, track back to the previous pick. By tracking in the opposite direction we ensure consistency. If backtrack results in a different pick than the original, the tracker stops. 

• Deletion 
  Deletes all segments shorter or longer than an user submitted amount of traces. This is an effective way to reduce the size of the tracking dataset. The delete shorter option removes segments that does not contribute effectively to the surface generation, while the delete longer option enables tracking for generating 3D bodies. 

• Average 
  The average option is related to the amplitude stop criteria. Instead of looking at the current trace compared with the next, the average takes the average of the n preceeding traces for current trace position. 

• Deviation 
  When the deviation is checked the stop criteria algorithm will compare current calculated amplitude with the extreme amplitude value in the entire line data set. The tracker will stop if current amplitude deviates from the extreme with more than p percent. The percentage p can be adjusted by the spin box item immediately below. 

• Amplitude range 
  Sets the amplitude range allowed for a pick. If the amplitude is outside the range, the tracker will stop. 

• dT - Time difference 
  Sets the maximum time difference allowed between two picks. Assume that pick1 time = 1000ms and pick2 time= 1009ms. The tracker tracks from right to left. If dT is set to 8ms the tracker will stop at pick1 since (1009 – 1000)ms = 9ms. The increase option lets you increase the dT as you go further down in the cube, making the time difference allowed between two picks bigger. 

• dT - dt between best and 2nd best 
  Sets the minimum time difference allowed between current pick and the two possible choices for next pick. If the difference is small it means that the tracker has several likely options for next pick and it should stop. 

• d(dT) - Gradient 
  Sets the maximum rate of change allowed between two picks. Assume that pick1 time = 1000ms, pick2 time = 1009ms, pick3 time = 1015ms. The tracker tracks from right to left. If d(dT) is set to 4ms the tracker will continue at pick3 since ((1009 – 1000)ms – (1015 – 1009)ms)= (9 – 6)ms = 3ms. 

• Look ahead 
  When checked a stop in the stop criteria algorithm will not make it abort immediately: it will continue (look ahead) the next n picks. If they also cause the algorithm to stop it will do so. Otherwise it will continue. This way we are able to ignore the odd erroneous trace. 

Testing tracking parameters

Knowing how the tracking parameters work will only take you so far. Wether the objective of the tracking is to generate GIM seismic, GIM surfaces or 3D bodies, it is always important to test the tracking parameters on some inlines and crosslines first. Since the tracking process only takes a few seconds on any given inline/crossline, or 2D section, it is possible to effectively test the tracker interactively until the desired result is obtained.

To test the tracking parameters, make sure a seismic section is displayed in the Geocap graphical window. Click the Select button in the input menu of the tracking generation interface, and click on the seismic section with the crosshair in the graphical window. You will see e.g ->inline2000 at the end of the seismic dataset field, when you have selected the seismic section.

Click Next and set the tracking parameters. Then click Next, Next and Run. After a few seconds the tracking will be displayed on top of the seismic section. Evaluate the result by zooming into different parts of the seismic section and look for different anomalies and breaks in the reflectors. Adjust your parameters accordingly by going back two steps with the Back button and repeat the process. When you are happy with one section, try the same settings on a few other seismic sections.

Generate tracking for surfaces

Generating surfaces is very much a balancing act. One wants the tracker to be generous and generate long lines giving us large surfaces. But at the same time we do not want the tracker to make mistakes. In most cases we would sett the tracking criteria to MinMax, Both ways, Gradient tracking and Delete segments shorter than 10 traces, but if you want the tracking generation to run faster you should select only one polarity (min or max) when setting the Snap mode. As a stop criteria we normally just use dT or d(dT). Finding the right parameter to use will require some testing as explained in Testing tracking parameters, but as a starting point you can try to set dT to 8-10ms or d(dT) to 4-6ms.

After testing the tracking parameters on a few seismic lines you can track the whole cube. Go back to the input menu and edit the input settings. For most cubes we recommend using an inline and crossline distance of 100m, as a starting point. This means we would set the Interval InLine and Interval Cross Line to 8 on a cube with an inline and crossline spacing of 12.5m.

Generate tracking for 3D bodies

To make 3D bodies, we want to omit the data which is interpretable. We invert the tracking so that all good data is removed, and we are left with the noisy bits of which we will make bodies. Often we use a tracking criteria with MinMax, Increasing, no Gradient tracking and Delete segments longer than 6 traces, combined with a stop criteria of e.g. dT set to 6ms. Of course you will have to test these settings as explained in Testing tracking parameters.

As with tracking for surfaces we recommend using an inline and crossline distance of 100m, as a starting point. This means we would set the Interval InLine and Interval Cross Line to 8 on a cube with an inline and crossline spacing of 12.5m. We only generate tracking in one direction when tracking for 3D bodies, either inline or crossline. You can do this by unchecking the crossline or inline option in the output menu.

Generate tracking for facies attribute

To make facies attribute, we only generate the tracking in one direction, either inline or crossline. One recommended method to get exiting results is to combine a strict tracking criteria, e.g. a dT of 3 ms, combined with a “remove short” set to 10 traces. This will make lots of breaks in the tracking as well as remove all parts of the data where GIM cannot generate interpretation lower than 10 traces.