Depth Conversion FAQs | Velit & VelPAK for IHS Kingdom and Petrel

Frequently Asked Questions: Velit


Getting Started With Velit

A good place to start with Velit is the tutorial, which gives a good overview of many of the key features in Velit, including depth conversion techniques, running multiple realisations of the depth conversion and the High Definition volume generation utility.

You can get to the tutorial document, Velit_tutorial.pdf, directly from within Velit, under the “Help > Explore” menu option.  There are some other useful documents there as well.

The tutorial model referred to in the document can be found in the relative folder path: ..\..\data\veldir\Base  Unzip this data to a folder location you have read/write access to.

There are a growing set of videos available on our YouTube channel that demonstrate various software features, some as quick “How Tos” and others as more in depth reviews.  You can best access these via and then clicking on the YouTube icon in the top-right.

Preparing Data for Velit

There is a section in the Velit Tutorial PDF on data preparation, found under the Velit Help > Explore menu, that goes into detail, but here us a summary.

1. Grid Creation

  • Grids should be created from the key horizon interpretations on your 2d & 3d surveys.  Only use horizons where it looks like you have significant velocity changes (based on your well logs and/or seismic velocities).  Typically, 3 to 6 grids are used.
  • Ensure the grids are created using the parent grid option in Petrel so that each grid has the same cell size and origin (and ideally the origin should be an even multiple of the cell size).

2. Wells

  • One or more wells with a cleaned & edited sonic log (Vp) and/or a T-D curve derived from check shots.  If the sonic logs are reasonably long, use those, otherwise use the TD curves.
    • If you have generated synthetics, apply the resultant T-D curve to the sonic log to give a calibrated sonic log for the best well velocity data to use.
  • Formation tops corresponding to the grids from above should also be present in each well, ideally with the same marker name.

3. Seismic velocities [optional]

  • If they are in SEG Y format, load them into the Petrel project & they are then easy to import into the Velit model.  Later version of Velit support both SEG Y and ZGY (realized) formats.
  • If the velocities are ASCII files, they need to be reformatted into columnar format.  Velit has a tool to do this – if you can send me an example file, I can record the steps on how to reformat the files for you (this will save time during the WebEx).
Where are my VelPAK models stored within TKS?

You can find the model in your Kingdom project folder, under the following path:


Here you will find your models (the *.bin) files, and for each .bin file a folder with the same name.

Language Setting for Windows - My data is not reading in correctly because I do not have my keyboard set to English!

Caused by the language setting for Windows. Specifically the problem relates to having a decimal point separator which is a comma “,” as opposed to having a period “.” which the applications were written to work with.

The applications are being modified to handle this in future releases but in the meantime you will have to either:

  1. a) Set the Regional and Language Options to be some English flavour


  1. b) Customize your current setting so that the decimal separator is a period “.”

Do this from the Regional and Language Options in the Control Panel for Windows.

You will need to re-import all your data once you have changed the settings.

Input / Output

Why have my Line Names and Well Names come across from Kingdom with double underscores in?

VelPAK can not have any embedded spaces within Line Name or Well Name. The Link can deal with spaces but must convert the spaces to characters.

‘[space] ‘ goes to ‘_’

‘_’ goes to ‘__’

‘:’ goes to ‘_:’

The reason for this is so the data can be transferred back again to TKS correctly by stripping off the added underscore.

Well Tops seem to disappear when inputting further tops using Merge or Replace

Both Merge and Replace for well tops appear to do the same. They work – BUT it appears they haven’t worked because the tops suddenly disappear from the display for the well you are Replacing.

This is because the Property Grid display for Wells has set to ‘Hide Unused Tops’ – and because Layer Definition been done on the data and suddenly these tops are not part of any Layer Definition they don’t show up any more.

Importing ASCII Stacking Velocities Into VelPAK

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.

Importing Average Velocities into VelPAK/Velit

The standard GUI assumes the incoming velocity volume is an RMS (stacking) velocity volume.

Use the following procedure to import the data as an average velocities:

  1. Import the average velocity volume as per usual as if it were RMS velocities; the import procedure creates an ASCII file on disk of inline/xline/time/RMSVelocity
  2. Delete the velocities from the model (Edit > Delete Stacking Velocities > All Lines) then save the model  (this is to ensure that if the Dix fly-out is used by mistake or in a workflow, the real average velocities aren’t overwritten).
  3. Go to the model folder and locate the “import” subfolder
  4. Edit stacking_velocity.dat using a text editor, and insert two columns of zeroes before the last column (so you have inline/xline/time/0/0/Velocity).  The last column will be read by VelPAK/Velit as Average Velocity (the 5th column is read as depth).  You can use ScanIt or a column editor such as “cream” if the file is too big for Excel.
  5. In Velit/VelPAK, use “File > Import > Profile Stack…” and select the edited file; don’t forget to select the corresponding survey in the “Prefix” dropdown.

The velocities are imported as average; on the velocity display, you can plot the average velocities, convert them to XYZ data etc. as per usual.

Can you give me workflow of exporting the velocity volume that I created in VelPAK to import it in TKS to use it for dynamic depth conversion?

You can generate a velocity volume from your model using the “Velocity” tab, then the “Volume” fly-out.

First, select the survey using the “Survey” option; this will cause the survey extents to be filled in the remainder of the dialog.  You can then manually adjust the Inline & Xline Min/Max values for the volume you wish to generate.

Time_Increment is the sample rate in milliseconds the volume will be generated at, and Time_Max is the time in milliseconds to generate the volume down to.  Adjust these to match your seismic volumes in the Kingdom project.

Change Dimension to Average, as average velocity is the most convenient velocity volume for using in Kingdom, then set the filename in the File field.  Press Apply to generate the volume as a SEG Y file.  You can also use the Batch Execution (lightning flash) icon to generate the volume in batch, using multiple CPUs.

Once the volume generation is complete, there will be a SEG Y file in the “volume” folder of the model directory.  You can import this into Kingdom as a seismic data type using “Surveys > Import SEGY Y…” in the usual fashion; use the default options for the SEG Y import, but ensure you store the volume as 16-bit or 32-bit, as 8-bit isn’t good enough to hold the dynamic range of velocities accurately.

Batch conversion of grid files to ZMAP format

If you wish to import CPS1 grids saved to disk in multiple realisation runs, directly to Kingdom or Petrel, you can convert them to ZMAP format.  There is a tool to do this built into Velit, but to do lots of grids for lots of multi-realisations is time consuming.

There is a one-line batch file “ConvertToZmap.bat” available from which can be sent through to enable you to do multiple grids. Please contact us and we will send it to you.

The CPS1 format grids are stored in the <petrel.ptd>\velit\<model-name\grid\eventXXX folder.

Unzip the file “ConvertToZmap.bat” to the folder containing the CPS1 grids, then double-click to run it.  It will convert all the files ending with “.cps1” into zmap files ending with “.zmap”.  You can then import these directly into Petrel or Kingdom.

TKS Link

How to Import Interval Velocities and Average velocities via TKS link into VelPAK?

Use the “File > Open TKS…” wizard as per usual, and ensure “Select 2d Seismic” is checked on the first page.  Proceed as per usual, but on the screen titled “Seismic Processing Velocities“, drag the lines (or whole folder) with the interval velocity data type (in the screenshot below, called “Velocity“) into the seismic velocity folder on the right-hand tree.  Then ensure “Generate Processing Velocities” is turned on & set the “Velocity Type” to “Interval“.

Specify the vertical decimation – 100ms is usually ok, but this may vary depending upon the geological complexity.

TKS Velocity Type

Proceed through the Wizard until everything is loaded into the model.  On the “Surface” display, turn on the “Line” and “Velocity” overlay to see the locations of velocities loaded (pink blobs).

Set the “Edit Mode” drop down to “Velocity” then click on the pink blobs to check the values at that location.  Pay attention to units of the velocity, as sometimes velocities may be in e.g. feet/s in a metric project.

Other Velocities that can be read in through this entry point in the TKS link:

RMS (Seismic Velocities) – will need to be processed through the Dix module within VelPAK to calculate the Interval Velocity and Depth.

Average – will calculate the Time-Depth pairs on reading into VelPAK and will not require Dix to be run on them.

None will read any volume values into VelPAK and place this value into the RMS storage slot within VelPAK. They will not be RMS velocities! This option simply ‘borrows’ the slot for storage within VelPAK.  These values can then be interpolated to produce a XYZ file in VelPAK from the XYZ routine within the Volume module by selecting the RMS as the Type of Z to be extracted from the slice:


Petrel Link

Producing Stacking Velocities in Velit from a Velocity SEGY cube in Petrel

Contact for the step-by-step guide to this.


Grid incompatible in Wizard


The grids must have the same AOI.  When you go through the import link, it resamples to the same AOI for you, but it doesn’t do this with a manual import.

You’ll need to re-make the grids in Kingdom to match the same AOI & cell size as the existing grids.  Alternatively, you could re-grid them in Velit, but the former option is usually best.

Delete any grids in the model without the same AOI as the Time grid in the model tree, as sometimes intermediate grids can be generated that then continue to cause problems.

When I update my Layer definition, how can I reset the Wizard, way that it shows the new layer definition?

I calculated an 8-layer case in the Wizard. Then I changed the layer definition to a 7-layer case by just taking one layer out (I set that layer to not used on the left side of the layer definition). But the Wizard still shows the 8-layer case. How can I reset the Wizard, way that it shows the new layer definition?

The Wizard is based on the grids in the model, not the layer definition.  Therefore you will need to completely remove the grids for the unwanted layer from the model, then move all the shallower grids up by one layer.

If you have removed e.g. layer 7, you can copy and paste the Time surface from layer 8 into the layer 7 (right-click on the grid > Copy, then right-click > Paste into the layer 7 slot).  Delete the remaining data from layer 8, close the Wizard window, then then re-run the Wizard for layer 7 using the layer 8 method.

If you have removed e.g. layer 2, it would be probably easier just to rebuild the model without layer 2, since you know which methods you wish to use.


My Looping Workflow keeps telling me that the optimisation results are invalid and I should regenerate!

The trick is to ensure you run the workflow first without any looping in it; i.e. strip out all the looping components from your workflow, save as another name, then run it.  Then run the looped workflow and you should be fine.


How do I display a seismic backdrop in VelPAK Profiles?

Define the current Survey geometry

In the Velocity >Volume tab, click the yellow folder icon and select the survey from the popup list.

velocity volume

If no survey is displayed, you will need to re-import the profile data into the model using (File>Open TKS…)

Define the SEGY file to display on the Profile display

Export the seismic volume to use as a backdrop from Kingdom (Surveys > Export  > Single SEGY….)

If it is a Time profile, you need a time domain SEGY file

If it is a Depth profile, you need the depth domain SEGY file.

On the Profile display, select the appropriate profile to display. Open the Display fly-out & set the following fields, setting them from top to bottom (the order is important):


Seismic_Colour is the colour table to use for the seismic; you may get an error message, but click “Continue” then select a colour bar.

Seismic_Type is the style of display; select “Density” for a colour display etc.

Press Apply, and the seismic backdrop should appear:


As you page through profiles, the backdrop will be displayed accordingly.





Velocity Volume Generation - Can Velit create a 3d velocity cube from 2d stacking velocities?

This is a straightforward workflow for Velit. Simply import the stacking velocities for the 2d lines, generate a velocity model for that, and then design a pseudo-3d survey over the area of interest with 3 corner points, cell size and vertical increment. Velit can then populate this pseudo-3d with the 2d velocities which can then be exported to SEGY.

I can't perform Dix - is it because I have no layers in my model?

have the 2D stacking velocities in Velit and I can display them but the options to perform Dix appears to have vanished. Is this because I don’t yet have any events/layers in my model?

Yes, you’ll need layers in the model; bung in dummy flat grid at max time e.g. 5 seconds to trick it.

I have multiple 3D, how can I select multiple 3D from the velocity – volume fly – out to generate the velocity volume?

If you open the Volume fly-out and click in the surveys box and then press the little icon, if you get a pop up with no surveys, the survey geometries are missing. You can easily fix this:


  1. Save the mode (just in case!)
  2. Use “File > Open TK… > Merge Mode
  3. Toggle off everything except the 3d Surveys box
  4. Step through pressing next until you get to the Surveys import page
  5. Drag each 3d survey you need from the left tree to the middle tree
  6. Press Next, Next then Finish

The surveys should then be listed in the Velocity > Volume > Survey box; you select a survey, generate the volume, then select the next survey etc.

The surveys are listed in the survey, but how I can select Multiple surveys at one time to generate one velocity SEGY volume from multiple surveys.

You’ll need to make a dummy survey in the Kingdom project that covers all the 3d surveys.  Ensure your grids cover the same area.  I’d make sure the inline/crossline spacing is quite large so the final volume doesn’t end up to be huge.  Then import that into the model as per the instructions before, and generate the volume for the dummy survey.

However, Kingdom will limit your use of this survey, but you will be able to visualise it etc.


How do you make Fault Allan diagrams in VelPAK?

Please contact for a document about this.


What are the preferred DT-log units: microsecs/m or microsecs/ft?

Velit always assumes that the sonic log is in microseconds/foot, even if the vertical units in the Kingdom project are metres. In the latter case, Velit will scale the log appropriately so that the displayed velocities are in metres/second.

Why don’t my Well Tops match up with my seismic event horizons on the Well Display?

You are using a sonic log – you need to calibrate the sonic log to a seismic event horizon.


How to import ASCII velocity file for building a Hi-Def model in K2018?

HiDef requires a SEG Y volume as the background model, it doesn’t work with ASCII.

If the ASCII files contains dense data (i.e. every velocity sample for every trace in the survey), you could import this into Kingdom as a seismic velocity data type and then use that with HiDef.

If it’s a sparse data set (i.e. not all traces in the ASCII file), there will be gaps in the Kingdom data type so that won’t work.  In this case, you’d have to use VelPAK to build a velocity model from it, then generate a SEG Y velocity volume, which can then be used by HiDef.

Note – it could be quite time consuming to do this. 

Depth Conversion

How do I update my time grids in a VelPAK model? Will I have to set up the entire depth conversion again?

If the grids are simply updated (as opposed to introducing more grids into the model), it’s straightforward to import the new time grids into the model and re-do the depth conversion.  All the parameters used by the depth conversion are stored in the model and won’t be lost when importing the revised grids, but there are some important caveats outlined below.

Before importing the new time grids, ensure they have the same cell size and extents as the grids used in the original VelPAK model.  In VelPAK, click on a grid in the model tree and look at the ‘Properties’ table below to see this information. To get the new time grids into the VelPAK model, use ‘File > Open TKS…’, toggle on ‘Select Grids’, toggle off everything else and ensure that the ‘Data Import Mode’ is set to ‘Replace’. Work through the wizard as normal, ensuring the replacement grids go into the same layer numbers as the original grids.

What happens now depends very much on how the original depth conversion was made.  If it was done via a workflow, simply load and re-run the workflow using the new time grids, and everything will automatically be updated (and the caveats below will be accounted for).

However, if the depth conversion was done ‘by hand’, if the grids have changed at any of the well locations, redo the layer definition in the ‘Layer’ module.  Then any residual error correction in the model will have to be recomputed.  This is easy enough, but takes several steps per layer in the model. For each layer:

  1. Go to the Surface module Depth fly-out.  The depth conversion parameters will be set there.  Ensure that the ‘Input Error’ is set to zero, then press ‘Apply’ to depth convert without using the residual error correction
  2. Re-compute the errors at the wells (Well module, Tie > Apply) – errors are stored in the XYZ Error slot
  3. Re-generate the error grids from the XTZ error data (Surface > Grid)
  4. Re-depth convert using the updated error grids (Surface  > Depth & set ‘Input Error’ to the new error grid).

After each layer has been depth converted, save the model again, then transfer them back into the Kingdom project tree using ‘File > Save TKS…’.

These important caveats may or may not apply, depending upon how much and where the grids have changed:

  1. If any of the depth conversion methods use ‘apparent’ interval  velocities (e.g. “Interval Velocity vs. Depth to middle of Layer”), where top depths and grid times are used, if the grids have changed at the well locations then obviously the apparent interval velocities may have changed.  In this case, go into the Curve module, open the ‘Generate’ fly-out, erase the current graph then press ‘Apply’ to regenerate the plot, before hitting  ‘Surface > Depth > Apply’.
  2. The above also applies if Optimisation was used; go to the Optimise module, open the ‘Generate’ fly-out and hit ‘Apply’ to re-run the optimisation before using ‘Surface > Depth > Apply’.
  3. If stacking velocities have been used, changing the grids will change the interval velocities computed, so the  interval velocity XYZ data will need to be regenerated & re-gridded.
  4. If Profile data was generated from the time grids, these will need to be regenerated, as the horizons seen on the profile are separate from the grids.
How to depth convert using the “Salt Wedge Model 2” formula


The “Salt Wedge Model 2” function allows for depth conversion of a layer containing two mixed lithologies, a predominant layer and a subordinate layer (or layers) that may be variable in distribution.  The layer is defined as usual by a top and a base grid, but is unusual in that an isochron grid (i.e. a time thickness map) containing the distribution of one of the lithologies is also provided as an input to the function.

Extra Inputs

  • Isochron grid of one of the lithologies (matching the extents of the layer defining girds)
  • Velocity of the predominant layer (grid or constant)
  • Velocity of the mapped subordinate lithologies (grid or constant)



A typical scenario is in the Zechstein formation in NW Europe.  In the North Sea, this consists of fast velocity anhydrite rafts within a slower, more halitic layer.

In this illustrative section, the anhydrite layers have been picked by top & base using 4 different interpretation horizons.


If there are multiple rafts stacked vertically, more horizons may be required.

The isochron of the anhydrite layer can be computed by subtracting the base from top anhydrite surfaces for each horizon pair, and then summing up & gridding.  The isochron should be zero where no anhydrites exist, and the cumulative sum of the anhydrite time thickness layers vertically.

  • Import this grid into the Velit model into a slot (I’ll assume General 01) for the appropriate layer.
  • On the Surface display, open the pin-open the “Depth” fly-out, select the “Parameters” tab and set the “Formula” drop-down to “[General]SALT WEDGE MODEL 2” (& ensure “From” field is set to “User”).


You can see the inputs are for “hardrock isoc”, the usual “last time”, “time”, “depth” and “error” slots, and the “VS” and “VH”. VS and VH are velocities for the primary & secondary lithologies respectively.  In the Zechstein example, the slow velocity halites & faster anhydrites respectively.

Typically, the secondary (VH) velocity may be a constant (in this case I will use a very high 5900 m/s), but the VS velocity may be a constant or a grid.  If you have good well coverage, you can deselect wells that don’t intersect with any of the secondary lithology and use the Wizard mapping function to map out the well velocities to create this grid.

  • Copy the interval velocity grid to e.g. a General 02 slot, then turn the other wells back on as you may wish to perform residual error correction.
  • Fill out the depth conversion dialog as follows (many of the parameters will be defaulted for you). Remember the first time you do a depth conversion, set the “Error” value to zero.  The depth conversion computes the residuals which you can then grid and apply on a second depth conversion should you require.


  • Press the “Apply” button and the outputs will be computed.  The isopachs for primary and secondary layers are put into the General 03 & 04 grids, but you can change these (but be careful not to overwrite your input isopach or velocity grids in General 01 & 02).
  • If required, grid up the “XYZ > Error” values into an “Error” grid, then use this for the second conversion to tie the depth surface to the well markers.


How can I retrieve the V0 values at the wells in Velit?

You should be able to get a set of V0 values for your wells by doing the following method:

In the Optimise module:

edit-modeSelect Edit Mode – Point

user-editFrom the Point Edit options that appear select User Edit


Click anywhere on the display. A User Point will be created and a box to edit the values for the User point will come up. Edit this to your V0 and K of the gradient of the curve you have:


Now in the XYZ tab of Optimise module set it as shown:


Note the Output X and Y will go into the named slots in the Model Tree for the Surface you are working with. Fixed Y has given fixed values of the K gradient, but the X values have gone into the Depth Conversion Intercept slot:


Click on this XYZ slot and turn XYZ and XYZ label on under Layers Visible in the Surface Module



How do I depth convert fault sticks in VelPAK?

There are two ways to depth convert faults sticks in Kingdom. You can either generate a velocity volume using VelPAK and then use that to depth convert the surfaces in 2d3dPAK, or depth convert the fault sticks directly in VelPAK.

To depth convert the fault sticks you must use VelPAK profiles, which work with horizons and faults rather than grids.  Before detailing the steps required, it is worth mentioning that it is often considered good practise to re-interpret the faults on the depth converted sections, rather than use depth converted faults.  Typically fault sticks are under-sampled, and so the depth conversion can create unusually shaped sticks in the depth domain, especially if there are velocity contrasts across grids.

If you have created a velocity model with grids, this same model is used in converting the horizons and faults.  Depth converting horizons and fault sticks works on a line by line basis.  Load the line geometries into VelPAK using ‘File>Open TKS…’ in the existing model & select the surveys & horizons with the import option set to ‘Merge’.   For 3d surveys specify an inline increment of 1 to be sure to capture all the interpretation data (unless interpretation has been done on say every 10th inline, in which case specify the start inline with interpretation then 10 for the increment).  Then specify the horizons that match the grids used in exactly the same order & finish the wizard.

Open the profile module and the horizons and any fault sticks picked on that line should be displayed.  Before depth converting, it is necessary to ‘snap’ the profile i.e. create a sealed section.  Use the ‘Snap’ icon to do this.  Snapping can be easy or a time consuming process depending upon how ‘clean’ the interpretation is.  Use the ‘Snap’ fly-out and set the options under the ‘Expert’ section to ‘Yes’ to let the software automatically fix problems for quicker snapping, but be sure to review the final snapped sections.

Once the profile is snapped, check if any faults penetrate the deepest horizon. If they do, it is necessary to specify a ‘basement’ velocity so the end of the fault stick can be depth converted.  Set the current layer to 32 (“Basement”) and use the ‘Depth’ fly out to specify the depth conversion method.  The easiest option is to use ‘Simple Interval Velocity’ and specify a constant as the velocity (although I know some of our customers prefer to use a more complex method such as ‘Hyperbolic Tangent’, which retains a velocity gradient but keeps velocities within a sensible bound).

Then press the ‘Apply’ button on the ‘Depth’ fly-out to depth convert the horizons and fault sticks.  Do this line by line for a couple of lines before changing the ‘Snap’ fly-out to work on all unsnapped lines, snap them, then set the ‘Depth’ fly-out to depth convert all unconverted lines automatically.  You can use the ‘Display’ fly-out to flip the display from time to depth & fill with interval or average velocities (if you see a blank profile screen, check the domain!)

To move the depth converted fault sticks into 2d3dPAK, you need to export them using ‘File > Export >> Profile Fault > Depth’.  On the ‘Filter’ tab, specify the ‘velpak_to_geoquest_m7_2d_3d_faults.awk’ filter.  The exported faults can then be imported into 2d3dPAK as GeoQuest CardImage 7 format.  Be careful with the import merge options – I’d suggest renaming the fault sets for safety.