C.S.E.G. Geophysical Workstation SEGY Standards

Following is a list of the SEGY Standards Committee:

With the proliferation of geophysical workstations in the industry it was felt by several members that the standards for SEGY stack data should be re-examined and if necessary brought up-to-date. Accordingly a committee was formed to discuss standards for geophysical workstation SEGY data formats. The following is a summary of the committee's recommendations. This committee actually followed in the footsteps of a previous committee formed in 1987 to examine the same issue. Their findings can be found in the October 1989 issue of the Recorder. While their recommendations are still valid today, (in fact they form the backbone of this committee's report), it is evident to anyone involved in workstation data loading that the standards recommended are not being rigorously adhered to. Although the limitations of the SEGY format are well known, and are being addressed by the Petroleum Open Standards Consortium (P.O.S.C.), this committee felt that it was far beyond our mandate to suggest a replacement for the SEGY format. We also recognize that the thousands of SEGY tapes now in existence will probably not be updated to the CSEG standard. It is the hope of this committee that the standards outlined will be followed for all new SEGY data, but this can only happen if the consumers of this data (i.e., the oil companies) ask that their vendors adhere to the CSEG SEGY standard.

Suggested Standards for SEGY Tapes

2D and 3D data

1) 3200 byte EBCDIC header consisting of:

• Area name;
• Processing Center;
• Processing date;
• Datum elevation used for structure statics;
• Time to first sample; Processing history as detailed as possible;
• Survey datum (NAD 27, NAD 83);
• UTM Zone or central meridian;
• Header byte locations for critical items such as shotpoint, X Y coordinates.

2) 400 byte binary header containing at least:

3) 240 byte trace header

4) Sample values written in format indicated in (2) above. Record length and sample rate fixed for each line. Inter-record gap between tape blocks (Tape media only). One trace per block.

5) EOF.

Each line written to tape should follow the above sequence with one EOF between lines and 2 EOFS after the last line. Subsequent tapes in multi-tape volumes should have EBCDIC and binary headers at the start of each tape.

Suggested Standards for SEGY Trace Headers

The following should be the minimum information in each trace header for 2D stack data:

The following should be the minimum information in each trace header for 3D stack data:

The outside label of a SEGY tape can be an important source of information about the tape or extremely vague and misleading. The following standards are offered as a guide to the minimum information that should be found on a tape label.

The following should be the minimum information on the outside label of a 2D stack tape:

1. Area name
2. Company name
3. Line name(s)
4. Processor
5. Processing date
6. Type of processing (At least stack or pre-stack, as extensive as space permits)
7. Tape density (Important for 8 mm tapes as well as 9 track)
8. Record length in ms
9. Sample rate in ms
10. Format (Floating point, Integer)
11. Shotpoint range (From first trace to last, not just field shot range)
12. Shotpoint scalar (1000)
13. Trace number within line
14. Tape number in multi-tape sequence.

The following should be the minimum information on the outside label of a 3D stack tape:

1. Area name
2. Company name
3. Prospect name (If different from area name)
4. Processor
5. Processing date
6. Type of processing (At least stack or pre-stack, as extensive as space permits)
7. Tape density (Important for 8 mm tapes as well as 9 track)
8. Record length in ms
9. Sample rate in ms
10. Format (Floating point, Integer)
11. Number of CDP bins
12. Line range (May be referred to as columns, inlines, north-south lines, etc.)
13. Trace range within line (May be referred to as rows, crosslines, east-west lines, etc.)
14. Orientation of this data set (north-south or east-west)
15. Azimuth angle of this data set (Use at least 5 decimal places)
16. Bin size in both directions
17. X Y coordinates for all four corners
18. Tape number in multi-tape sequence
19. Indicate if dead traces dropped.

The following items are desirable but not essential. Applies to 2D and 3D labels:

1. Header byte locations for critical items such as shotpoint, X Y coordinates, row column
2. Survey datum (NAD 27, NAD 83)
3. UTM Zone or central meridian
4. Time to first sample.

If SEGY volumes consist of multiple versions of lines the version of the line that is most likely to be loaded onto a workstation (e.g., filtered migration) should be the first file on tape followed by the other versions in descending order of loading probability (e.g., filtered structure stack, unfiltered migration, unfiltered structure). With multiple lines all the lines of each processing type should be grouped together to facilitate data loading (i.e., all the filtered migrations followed by all the filtered structures, etc.).

If SEGY volumes consist of multiple versions of lines the version of the line that is most likely to be loaded onto a workstation (e.g., filtered migration) should be the first file on tape followed by the other versions in descending order of loading probability (e.g., filtered structure stack, unfiltered migration, unfiltered structure). With multiple lines all the lines of each processing type should be grouped together to facilitate data loading (i.e., all the filtered migrations followed by all the filtered structures, etc.). The aim of the committee was to publish a reasonable standard that could be adhered to by all parties without making major software changes. Accordingly we have avoided changes to the existing standard. The only item in the above standard that is new is the additional option for the flag in the binary header to denote IEEE floating point. Most if not all seismic processing and tape copy centres are capable of writing SEGY data to this standard now. It is up to the industry to encourage them to do so.

The committee wishes to thank the C.S.E.G. Executive for encouraging our work and also gives thanks to the members of the previous committee for their efforts. We thank all the people in the industry who offered their views and advice.