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:
- 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
- Re-compute the errors at the wells (Well module, Tie > Apply) – errors are stored in the XYZ Error slot
- Re-generate the error grids from the XTZ error data (Surface > Grid)
- 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:
- 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’.
- 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’.
- 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.
- 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.