Data exchange file formats – Seismic Operations

Seismic Operations – Data Exchange Formats

Over the last four decades or so industry bodies (UKOOA, SEG, IOGP) and industry companies (Shell) have published a series of positioning data exchange file formats that enable seismic positioning data to be the exchanged between vendors, clients, government agencies etc.  The formats provide a structured mechanism of presenting positional data, event numbering and time of event.  The formats also provide structured fields to capture metadata (data about data) often referred to as the file header.   The metadata will comprise, among other items, details of the coordinate reference system to which the positions within the data block are referenced.

Data acquisition

A successful seismic survey will comprise three principal elements, namely:  Amplitude, Time and Position: Seismic triangle

With respect to position, there are two key elements whose positions must be determined, namely: source positions and receiver group positions.   Having determined these positions it becomes possible to determine the position of the ‘common mid point’ for each source-receiver group combination.

Positions are determined by making survey observations, typically ranges, bearings and angles.  The observations are subsequently used within a processing flow to compute the positions of the source and receiver groups.  Further details of all these operations are given within the seismic acquisition tutorial.

 

Data storage

Survey and positioning data is divided into two categories, namely:

  • Raw data files (also known as pre-stack files) – raw data refers to the actual survey observations that are made, e.g range, bearings and angles.  Survey observations are made using equipment deployed during seismic acquisition at strategic geometric points to ensure optimal determination of the source and receiver groups.
  • Processed data files (also known as post-stack files) – the raw data is used within processing flows to determine the source and receiver group positions.  These positions are stored within the processed data files that ultimately constitute one of the final deliverables from the seismic survey.

 

History

Formerly, there were two main industry associations that published file formats to capture the raw and processed survey and positioning data, namely:

  • United Kingdom Offshore Operations Association (UKOOA)
  • Society of Exploration Geophysicists (SEG)

Raw navigation files

The raw file formats capture the raw observations and event information acquired during the running of the seismic line.  These formats were specifically developed for marine towed seismic surveys and the different vintages (1986, 1991 and 1994) reflect changes in the format to accommodate newer acquisition techniques, e.g. multiple streamers, acoustic networks and advances in DGPS data capture.

UKOOA:  P2/86, P2/91, P2/94

SEG: SEG-P2

 

Processed navigation files

UKOOA: P1/78, P1/84 and P1/90

SEG: SEG-P1

 

In addition to the industry associations, Shell Oil Company also produced their own data exchange format known as the SPS format (Shell Processing System).  The format comprises three individual files produced for each seismic line acquired. These are known as the r file, s file and x file.  The first two contain positions for the receiver groups and source groups.  The x file is known as the relational file and described the geometric relationship between the receiver groups and sources.  Basically, what receiver groups were open and listening when each shot point was fired.

 

3D seismic surveys – bin grid definitions

UKOOA:  P6/98

 

 

Recent changes

In the mid 2000’s UKOOA and EPSG were absorbed into the already existing Association of Oil and Gas Producers (IOGP).  One of the technical expertise sections within IOGP is the Geomatics section.  With the absorption of UKOOA, the IOGP Geomatics committee became custodians of the positioning data exchange formats and added to this were the SEG positioning formats and the SPS file formats.

In the late 2000’s Geomatics committee set about producing a new series of formats to supersede the existing outdated formats.  This brought raise to the Px/11 formats of which three formats were developed for seismic operations, namely:  P2/11, P1/11 and P6/11.

These new formats broke from the traditional rigid column formatted files to produce a more flexible comma delimited format.  This brought to advantage of not restraining many of the variables to a fixed limited format, for example the number of characters that could be assigned to the seismic line name or the number of digits assigned for the storage of coordinates, thus reducing the resolution of precision.

The documentation associated with these file formats is available from IOGP web site.

 

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