Introduction

Petrel will load the SEGY files generated by the sub-bottom system so that these can be incorporated into a project that includes the site survey seismic, core and logging data. This assumes that a project already exists with at least the basic information that is needed (map projection etc) – these are covered in the Petrel manuals if not.

The online SEGY files are likely to be easier to load into Petrel than those generated by ODC-SEGY conversion later. However the principles are the same.

Procedures

1. Start Petrel and load the existing project
2. Right click on the appropriate seismic data folder in the Petrel project. Choose “Import (on selection)” with the “SEGY Toolbox” option. The other SEGY load options won't extract the navigation information.
3. When the SEGY Toolbox starts, the first thing is to sort out Byte positions – click on the “Define” button. Set Trace number, SP number, CDP number all to 9 – this is the only trace header that is properly set. Leave X and Y coordinate as they are. Don't do anything with the “advanced” options. If you click “scan” you will get line graphs that hopefully relate to what you think you collected. Then hit OK.
4. Navigation source will be SEGY trace coordinates
5. In SEGY overrides click on Headers and check the box for “Zero coordinates” - the link to navigation is often problematic
6. The Input File CRS will be WGS84 – the easiest way to choose this is to click on Select and type “geodet” into the filter
7. Finally click on “Run” and the SEGY toolbox will translate the coordinates into the trace headers in the correct CRS for your project, and as long as you have “Load generated SEGY files to Petrel” checked the data will appear immediately in your catalogue.
8. Check as for any other new import (map, interpretation window). Note that the data are processed to be the envelope, ie only values >0 are present. Note also that the SEGY file that Petrel actually uses is in the “Output SEGY directory” location, not where the original data source was.

If you are using data from the SEGY conversion you will probably encounter a range of problems. The most serious is that the program occasionally puts in traces with different length or sample interval or both. You might be able to handle some of these with the SEGY overrides. Otherwise you will need to use a seismic processing package to fix the problems. For example this is a set of commands I used in Seismic Unix (a free processing package) to clean up data during Exp362:

 segyread tape=20161001134130P_zoom-LF-2.seg endian=0 | suwind key=fldr min=400 max=6120 | suwind key=dt min=200 max=300 | sushift tmin=5.4 tmax=5.7 | suximage perc=97

 segyread tape=20161001134130P_zoom-LF-2.seg endian=0 | suwind key=fldr min=400 max=6120 | suwind key=dt min=200 max=300 | sushift tmin=5.4 tmax=5.7 | segyhdrs bfile=binary2a

 segyread tape=20161001134130P_zoom-LF-2.seg endian=0 | suwind key=fldr min=400 max=6120 | suwind key=dt min=200 max=300 | sushift tmin=5.4 tmax=5.7 | segywrite tape=fixed_chirp2.seg endian=0 bfile=binary2a

Credits

This guide was originally written by Timothy Henstock (2016; Exp. 362 Logging Scientist)

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