ASCII stacking velocities cannot be converted to a SEG Y volume anywhere in Kingdom, or loaded into the main project database (unless converted to grids).
The stacking velocity ASCII file must conform to a simple, columnar format.
For 3d: Inline crossline time velocity
For 2d: Linename SP time velocity
where time is the time in MILISECONDS (not seconds!) and the velocity is in either metres/second or feet/second (matching the Kingdom project units).
Often files aren’t provided in this format, but they can be reformatted using the VelPAK ‘Tools > Scanit’ utility. The Scanit program has its own ‘Help’ menu which features some guided walkthroughs for using this tool. It can be tricky to get to grips with! If you have trouble using it, please forward your stacking velocity file onto the support team who can reformat it for you.
Before loading stacking velocities into a VelPAK model, be sure to load the survey(s) required into VelPAK by using ‘File > Open TKS…’ and turning on the ‘Select Surveys’ option.
For 3d surveys, VelPAK defaults to loading the co-ordinate information for every 10th inline. Inspect the stacking velocity file and see if it is decimated. To load all the velocities VelPAK must have loaded the corresponding trace coordinates from Kingdom (it won’t interpolate the cords).
For example, if the survey starts at 4154 but the stacking velocity file starts at 4160 and skips every 20th line, ensure you load the survey starting at 4160 with an increment of 20. If in doubt, load the entire survey by setting the inline increment to 1, it won’t affect performance significantly unless you are using the VelPAK ‘Profile’ mode.
Note that all trace coordinates are loaded for each inline, irrespective of the crossline selection, so you don’t need to explicitly load crosslines (unless you are dealing with complex profiles in the crossline direction).
Once co-ordinates are loaded, then proceed to load the stacking velocities using ‘File > Import > Profile Stack….’. Select the stacking velocity file, then for 3d surveys, ensure you set the ‘Prefix’ for the correct survey at the bottom of the dialog – it’s easy to miss.
For 2d lines, the survey name is in the imported file, but you do need to ensure the names in the file are an exact match for the names in Kingdom, or you will get an error message about coordinates not found.
Once the velocities are loaded, you can QC their position on the VelPAK ‘Surface’ map by using the ‘Layers Visible’ drop-down and toggling on ‘Velocity’. You should see pink blobs at the trace locations where stacking velocities occur (if there are blue ones, don’t worry about that, it just indicates they are located on the currently active line).
To QC velocity values, set the ‘Edit Mode’ drop-down to ‘Velocity’ then left-click on a pink blob to see a one-line summary in the ‘Console’ window, or use the middle-mouse button to see a pop-up of the values at that location.
To display the velocities in profile, open the ‘Velocity’ tab and you will see velocities for the current layer in the VelPAK model. If you click the ‘Surface’ tab (under the model tree) and set ‘Surface’ to 0, you should see all the velocities in the model plotted. Use the ‘Display’ fly-out and set ‘Well_overlay’ to ‘Yes’ to compare with well velocities.
Once the stacking velocities are loaded, there are numerous ways of incorporating them in the depth conversion. Popular techniques involve making a grid of interval velocities for each layer, calibrating stacking velocities to the well velocities and then depth converting, making pseudo-wells from stacking velocities and modelling functions from those, or kriging well velocities using the calibrated stacking velocities as an external drift function. It is impossible to recommend a particular method, as it will depend upon the data & distribution of the data in the project, the geology, geophysical constraints etc.
A good place to start with stacking velocities is the workflow system.
If you have no well velocity data, the simplest workflow is ‘Dix IntervalVelocity Multi.xml’ which does a direct conversion of the layer using interval velocities derived from stacking velocities using the Dix equation (see ‘Kingdom > Help > Tutorials > VelPAK > VelPAK Glossary’) for more information on the Dix parameter. On the ‘Velocity’ tab, apply the Dix scaling factor to your stacking velocities to compute the Dix interval velocities, then run the workflow.
Here is a screenshot of the full workflow for a 3 layer model that is depth converted using the Dix interval velocities directly:
If you have well data, and have performed Layer Definition and well calibration to prepare the well data, then it might be worth trying the ‘Dix Smooth and Calibrate.xml’ workflow, which scales the stacking interval velocities to the well interval velocities to give a more realistic result.
As the workflow runs, you can interact with the displays to ensure outlier well velocities are identified and removed from the scaling computation. If you do stop the workflow to deselect wells, ensure you re-run the workflow for that layer so the layer is depth converted before moving on to the next layer.