New SEG-Y standard nearly final (August 1998)

Jill Lewis of Troika, the UK-based tapetranscription software specialists, heads the Petroleum Exploration Society of GreatBritain's (PESGB) initiative to extend and modernize the SEG-Y standard. Jill has suppliedPDM with the following progress report.

In 1997 when the PESGB Data Management Group was established, one of the subjects that arose was Data Exchange. It was recognized that a great deal of effort was wasted in the management of seismic information, especially as there was no widely accepted exchange format in which to write both the positioning and sample data. Although a number of attempts had been made to revise, update and/or replace SEGY none had been successful. This was partly due to the diversity of users, from a single user PC-based system to high capacity media robotics on a super-computer. The large amount of historic information currently in existence, approaching 25 years of format usage, added to the need for an update to the standard. Formats which had been tabled as replacements for SEGY such as the POSC Exchange Format (PEF) and SEGDEF had little take-up as they were generally felt to be too complex.

In September 1997, a group of interested people offered to investigate the current methods of seismic data exchange and whether the group could compile revised format which would satisfy the modern demands of data, yet remain backward-compatible. The SEGY Sub-Committee held a number of meetings, in close succession, before approaching the SEG at the Dallas SEG standards subcommittee meeting. Although there had been a number of attempts in the past to update SEGY, and it was recognized that this would be a very useful exercise, no-one was officially carrying out this work at the present time. The PESGB group requested permission to adopt this role and were given the approval of the SEGY technical standards committee.

To ensure that all those who wished to be involved in discussions could communicate we set up an e-mail reflector at Troika's offices. This e-mail site has 80 interested parties on it, a number of which in turn further disseminate the information, to the CSEG; Australian Workgroups Committee of our activities; and UKOOA. One of the most important data groups was positional information such as projection, CDP positions and 3D bin grids, which are to be included in human-readable form. Unfortunately, such information would have occupied most of the EBCDIC header which was unacceptable to many parties because so much of this header was already spoken for in the legacy implementation. More header space was required - a simple requirement but one which brought about some lively discussions.

Everyone wanted to maximize the human, and potentially machine-readable, headers but it was not clear how to do so. We had the problem of finding a method of adding more information but remaining backward-compatible. It was also considered desirable to maintain the "signature" of SEGY e.g. the 3200 and 400 bytes blocks. After much deliberation proposed schema uses a flag in the machine readable binary header which denotes the addition of extra machine and human readable EBCDIC headers. This is set to "0" when there are no further headers therefore being backward-compatible with historic data. We are now in a position to begin work on defining the 'stanza's' which will provide keywords and field definitions to enable the data to be machine readable. The following stanza's have been identified which will make up the new SEGY Revision 1.0

Dataset Overview

Projection

Survey Outline

3D Bin Grid

Data Parameters

Acquisition Parameters

CDP to Shot Point Relationship

Usage of Trace Headers

Binary Header Contents

This work is being carried out in association with POSC who have agreed to map this (if necessary via aliases) onto the POSC data model. This will probably be the final draft, containing as it does the ideas to be carried forward into a revised standard. The next stage will be to produce a more formal document that will hopefully be acceptable to the SEG, and other bodies, as a new revision of the SEGY standard. Resources are currently being sought to enable this next stage to proceed. More information and comments on this activity to Jill Lewis, Troika, jill@troika.demon.co.uk.