Depth conversion in Claritas:
The following page describes one method of converting a stacked TIME seismic section to a DEPTH section. This conversion requires a velocity model.
- SeisWide has a depth conversion utility that uses a velocity model created in SeisWide (or imported from Rayinvr). However, much better results have been obtained using Claritas (better agreement of velocity model nodes with converted section). Claritas is also designed for MCS processing, so it makes sense to be able to use the velocity file from Rayinvr.
- The first step is to create a 2d velocity model in Rayinvr RayinvrAnalysis. Once this is done, velocity profiles from this model can be created using Vmodel (or Xvmodel). These should contain "traveltime, velocity" points for every offset sampled:
- The following parameters need to be set in "vm.in" (the vmodel parameter file): "ivp=1" (to output profiles), "izort=1" (to output 2way time instead of depth), and "xvp=offset1,offset2,...,offsetN" (an array of the offsets you wish to sample at). See the rayinvr docs for detailed info.
- Running Vmodel with the previously mentioned parameters will yield a file "vm.out" which will contain the velocity profile information. The format is pretty strange, so here is a python script to convert it to a Claritas style .nmo file.
- »upload/rayinvr2claritas.py: This program accepts a simple xyz format text file, or the 'vm.out' format as input. It will convert either of these files to a Claritas .nmo format file (default), or an xyz output. It can also convert from offset to trace number.
- It is advisable to examine the new .nmo file with the Claritas program 'isovels' before using it in processing flows.
- Once the .nmo file has been created, it can be read into a Claritas job flow. Read in the segy file using readsegy described in ObsSegyProcessing. Use the process "TDCONV1" to do the actual depth conversion. Ensure that its using interval velocities, and that the coordinate scale for the segy file and the .nmo file are the same. The depth converted data can now be saved as a new segy file.
Example:
This example converts from the »vm.out input file (written from Rayinvr's vmodel) to a Claritas »vm.nmo output file, using trace numbers instead of offset (defined in the file »horizonOffset2.txt).
rayinvr2claritas.py --input vm.out --trace-file=horizonOffset2.txt --output vm.nmo
For help type:
rayinvr2claritas.py --help
