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Monday, 29 March 2010

New Standards: SEG-D 3.0 and the SEG Technical Standards Committee

Jill Lewis, Troika International Stewart A. Levin, Halliburton Drilling, Evaluation & Digital Solutions, Rune Hagelund, WesternGeco, Barry D. Barrs, ExxonMobil

Summary
The SEG Technical Standards Committee has recently undertaken a revision of the SEG-D Field Tape Standard designed to accommodate the needs of current and anticipated future acquisition systems. This includes not just field acquisition support for arbitrary sample rates, continuous passive recording, multicomponent sources and receivers, and sophisticated field filters, but also things like area / line /crew /client /job information, source and receiver co-odinates and their reference system, and capture of processing such as trace edits in the field system.

Introduction
A field systems engineer, an acquisition bird dog, a seismic processor, a seismic interpreter, a geoscience researcher and a software developer were having refreshments at an SEG International Exposition and Annual Meeting while discussing the state of SEG field and interchange standards.

"We generate essential quality control information in our field systems, but our customers never seem to pass it on to their clients. I really wish there were a standard place in the SEG-D format we can automatically record it. Right now we have to put in extra SEG-D headers in our own proprietary format." said the field systems engineer.

The bird dog agreed. "Yes, I couldn't do my job properly without your system's QC displays. Picking out trace edits is almost painless. It's a shame, though, that I end up putting this with the observation sheets on a separate CD or a USB stick and not directly on the SEG-D tape."

The seismic processor chimes in: "Speaking of observation sheets, I seem to spend half my time chasing them down. And don’t even get me started on geometry! Our navigation folks are so busy merging and QC'ing coordinates that none of them could even spare the time to come to this convention."

The seismic interpreter recalled that just last week she was trying to tie two different vintages of spec data over a prospect. "Something was clearly wrong with the header coordinates of one or both of the surveys, but no one was ever able to locate the navigation data to check on differences in datum or local zones. I ended up stretching and squeezing the two until they more or less fit. What an ignominious epitaph for hundreds of hours of TLC seismic data processing. And all because we couldn't get the nav."

The geoscience researcher, finally resting after running back and forth as much as half a mile shuttling between 10 simultaneous technical sessions, pulled out his pipe, put it back after noticing the no smoking sign, and sighed. "You know that by the time an SEG standard is published, it is practically obsolete. Our company has been monitoring producing fields with 9 C, 4 D seismic, both active and passive, for some years. But lacking any standard for formatting and transmitting it to contractors, we waste inordinate amounts of time and money getting it processed properly so I can get on with my research program of jointly analyzing these data with CSEM acquired at the same time."

The software developer harrumphed, took another swig of high caffeine double nonfat latte, and interjected "Wait just a minute, there. Do we really want a new version of the SEG-D standard upgraded to include the kitchen sink? The existing standard already has plenty of problems with ambiguities, mistakes and inconsistencies and you want to make it even more complex? Let's assume by some miracle this SEG-D on steroids is actually promulgated before I retire. Now I've got to spend the next year rewriting all the tens of thousands of lines old Fortran dating from the '70s for reading SEG-D. And just because there is more information in the new SEG-D, doesn't mean there's a place for it to be transferred into in the existing seismic processing and interpretation system. Add another two man years of development. And at least half my time after that maintaining and upgrading it to work around one vendor glitch after another. I'll welcome early retirement after that!"

SEG-D Rev 3.0 goals
As the previous imaginary conversation indicates in its tongue-in-cheek way, there is a clear need for standardization of additional seismic data and metadata in SEG-D to capture information that is automatically captured or generated in the field. Continuing the status quo of many vendor-specific extensions greatly increases the risk that that extra information will be indecipherable a decade from now.

Some features that the SEG-D upgrade to SEGD 3.0 now includes:

  • General survey information such as client, area, prospect, field crew or vessel,
  • Source type(s), strength, timing, status, layout, and field conditions,
  • Receiver type(s), orientation, sensitivity, status, layout and field conditions,
  • Support for IEEE 8 byte samples, code 8080,
  • Support for sample rate steps of 1 microsecond,
  • Four and a half years of recording data at one second interval to provide support for passive recording,
  • Support for CSEM and EM recording,
  • Common Time Stamp GPS Epoch, starting 6th January, 1980,
  • Clarification of method for writing data to disk,
  • Coordinates and their EPSG reference system in line with OGP (International Oil and Gas Producers Association),
  • UoM (Units of Measurements) Table in common with Energistics,

They are represented by:

  • Completeness: If implemented and populated the survey could be constructed later from the SEG-D.
  • Compatibility: Where reasonable, the format is compatible with earlier versions, both in layout and methods of extension.
  • Coordination: Where new (or old) information is in another technical standard? So that the information can be exported to or imported from the other standard without pain or degradation.
  • Clarity: We have avoided ambiguities by means of explanatory notes and examples. And don't specify the same information in two different places, a failing of the current SEG-D Rev 2.1 standard and its predecessors.
  • Simplicity: Adopt a set of consistently followed practices in laying out information in the new SEG-D revision. Make each block or block grouping self-contained, irrespective of any master table of contents.
  • Do no harm: Seriously consider how new SEG-D data might be misused or misinterpreted down the road. For example, how might preplan coordinates for source and receiver be mishandled?
  • Recoverability: Provide internal clues and make formatting choices that limit the loss of information should the medium on which SEG-D is recorded becomes corrupted.
  • Cleanup: Option to provide a precise count of samples per trace in milliseconds rather than ambiguously back calculating it from other fields in the headers.
  • Extensibility: Have a clearly defined compatible approach to future updates that can be quickly drafted, approved and deployed without revisiting all aspects of the existing standard.

The SEG is now working very closely with the OGP (International Oil and Gas Producers Association, ogp.org) who represent approximately 80% of the Oil and Gas producers from around the world. This association is the custodians of all the positioning formats with the SEG handing over the SEGP formats early in 2009. The OGP is currently updating the range of the positioning formats.

The OGP also hosts the EPSG (European Positioning and Survey Group) database which is freely available from their web-site providing geodetic parameters for the world.

The SEG and the OGP are some of the most valuable resources that are available free of charge to the upstream oil and gas industry. We are nothing without data and the more comprehensive the recording the better use we can make of that data. An enormous effort has gone into the work represented here over the last six years. By utilizing this work it is estimated that you are receiving in excess of four million dollars of free consultancy. If we included the EPSG database then this figure would more than quadruple.

This is a wonderful and free resource that will improve and save money in many departments including Acquisition; Data Management and Processing.

References
Note: All SEG technical standards are published on the website http://www.seg.org/publications/tech-stand/.

Allen, R., Crews, G., Guyton, W., McLemore, C.A., Peterson, B., Rapp, C.S., Walker, L., Whigham, L.R., White, D.A. and Wood, G., 1994, Digital field tape format standards - SEG-D, REVISION 1, Geophysics 59,
668-684.

Cavers, D.A., Carroll, P.E., Meiners, E.P., Racer, C.W., Siems, L.E., Sojourner, M.G., Twombly, J.L., and Faichney, Norris, Hiscox, Hovde, Bingham, Stigant, Racer, Reynolds, Hares, 2001, SEG-UKOOA Ancillary Data Standard - Metafile Format Description: Geophysics 66, 1961-1998.

Weigand, J.A., 1980, SEG-D—Digital field tape format standards, in Digital Tape Standards, Society of Exploration Geophysicists, 31-65.

SEG Technical Standards Committee, 1997, Digital field tape format standards (SEG-D Revisions 1 and 2), Society of Exploration Geophysicists, 46 p, ISBN 1-56080-046-1.

SEG Technical Standards Committee, 2002, SEG Y Data Exchange Format Revision 1, Society of Exploration Geophysicists, 45 p, ISBN 1-56080-123-9.

SEG Technical Standards Committee, 2004, Digital Tape Standards (SEG-A, SEG-B, SEG-X, SEG-C, SEG-Y, SEG-Y Revision 1, SEG-D, and SEG-D Revisions 1 and 2 formats), Society of Exploration Geophysicists, 112 p, ISBN 0-93183-015-X.
posted by The Rogtec Team @ 12:18 

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