Introduction to the OffshoreUKOOA and the
EPSG have been working together for many years. Through their collaboration, they have developed many standards and
UKOOA has been open to listening to the industry about positioning in the
North Sea.
When seismic data is acquired, whether it be
2-D or 3-D seismic surveys, the
shotpoints (
energy source, common mid-point, etc.) need to be positioned or referenced on surface.
Over the years
UKOOA has developed various formats, named
via a version and a year. This is a short introduction to how these files describe positions in the oil and gas industry.
UKOOA P1/90Information is described in the
Header for the file. The
Header records following the convention listed below:
Record Identifer "H" Column(s): 1 Format: A1Header Record Type 2-3 I2Header Record Type Modifier 4-5 I2Parameter Description 6-32 A27Parameter Data 33-80 VariesUsing the above as a basis, let us take a look at how
Datum and Spheroid information is described in this file.
Header records
H1600 and
H1601 are required for
Datum Transformation parameters used by the
Bursa-Wolfe Transformation.
Reviewing the Bursa-Wolfe Transformation (as vectors), we see the following:
X DX 1 -RZ +RY XY = DY + SCALE * +RZ 1 -RX * YZ DZ -RY +RX 1 Zwhere
X,Y,Z are geocentric cartesian coordinates defined in metresDX,DY,DZ are the translation parameters defined in metresRX,RY,RZ are clockwise rotations defined in arc seconds,but are converted to radians for use in the formulaSCALE = [1+S. (1oe-6)] where S is in parts per millionThe
Vertical Datum, is identified by Header record H1700. Some examples of the vertical datum, in relation to offshore work are:
LAT - Lowest Astronomic TideMSL - Mean Sea LevelSL - Sea LevelES - Echo SounderThe units of measurement are specified in H2001. These should be consistent with the position data. The height unit code will be 1 for metres, 2 for any other unit of measure. Header H2002 specifies the Angular unit code to 1 for degrees, 2 for grads.
Projection Data is specified in Header records H1800 to H2509
Currently, in this older format, the following projection codes were defined and used.
001 - UTM Northern Hemisphere002 - UTM Southern Hemisphere003 - Transverse Mercator (North Oriented)004 - Transverse Mercator (South Oriented)005 - Lambert Conic Conformal with one standard parallel006 - Lambert Conic Conformal with two standard parallels007 - Mercator008 - Cassini-Soldner009 - Skew Orthomorphic010 - Stereographic011 - New Zealand Map Grid999 - Any other projection or non-standard variation of the 11 listed aboveSince this initial positioning file was developed with the help of surveyors, they planned ahead and answered the question:
What happens when we cross the Equator?When a survey crosses from the South to the North, and the whole survey is shot on a Southern Hemisphere UTM Zone, the coordinates will possibly exceed 9,999,999.9. This is not acceptable in the P1/90 format, so Header record H2600 must indicate that 10,000,000 must be added to the co-ordinates.More detail about this specification can be found
here.
As the industry matures, new versions were released, the next in 1994. This was called p2/94 and was derived for raw marine positioning data.
UKOOA P2/94During this time,
differential positioning with GPS was just being implemented and the industry was beginning to rely on this technique more and more for offshore surveying.
This format is based on
UKOOA p2/91 and has extended many of the definitions needed for differential GPS.
As operators maintain and store data in these formats, P2/94 also acts as an archiving format and records information such as the
satellite ephemeride, ionospheric conditions and weather/meteorological conditions of the survey.
With the move to P2/94, Geodetic information moved to new headers, and are such described as:
H0100 Magnetic Variation - General InformationH0101 Magnetic Variation - Grid DataH011# Datum and Spheroid Definitionswhere # = 1..9 and is the datum & spheroid numberH0120 Seven Parameter Cartesian Datum ShiftsH0130 Other Datum Shift ParametersH0140 Projection TypeH0150 (Universal) Transverse Mercator ProjectionH0160 Mercator ProjectionH0170 Lambert ProjectionH0180 Skew Orthomorphic & Oblique Mercator ProjectionH0181 Skew Orthomorphic & Oblique Mercator Projection cont.H0190 Stereographic ProjectionH0199 Any other ProjectionSatellite System DefinitionsH600# Satellite System DescriptionH610# Definition of Differential Reference StationsH620# Satellite Receiver DefinitionH6300 GPS parameter recording strategyH6301 DGPS differential recording strategyH631# GPS clock and ephemerides parametersH632# GPS ionospheric model & UTC parametersH6330 Meteorological parametersH65## DGPS differential correction source defnH66## DGPS differential correction source defnH67@0 GPS ellipsoid height estimateRotation ConventionsNote that 2 different conventions are in use in the survey industry for defining rotations. This has led to considerable confusion in the
GIS and mapping world. Both are valid when used properly.
The two conventions can be referred to as:
1) Position Vector rotation (Commonly used in Europe and referred to as the Busra-Wolfe)2) Coordinate Frame rotation (Commonly used in North America)I will talk more about these on a later blog, as it comes into play with a lot of
GIS and mapping software.
More detailed information about the P2 format can be found
here.
UKOOA P5/94This version came along to facilitate the exchange of position data for pipelines,
flowlines,
umbicals and power cables offshore.
In these cases, the data required for pipeline positions are the
Latitude, Longitude, Easting, Northing, Depth, and Kilometre Point (KP), along with the standard datum and map projection parameters.Without wanting to bore my readers with more H records, you can found out more about how the pipelines are stored in this format
here.
UKOOA P6/98In 1998, a new version was developed for
3D seismic surveys and binning.
This is quite complex and would make this short blog even longer, so I'll write about this format at a later date.
The main emphasis of this blog, though, is to show how formats can change over time as technology and data sharing increases. It also points out the importance of knowing the format of your data, especially if you are doing historical work over a region - do not always assume a specific data format. This is partly why the
OGP has started the Joint Industry Project I mentioned in an earlier post.
UKOOA P7/2000Well's deviate. With the advent of horizontal wells and sidetracks, and relating to seismic surveys, we enter a whole other story again.
In this story, as well (bad pun!), we have to consider height
measures (such as Kelly-Bushing), and the 4 Norths (which I will explain on a later post).
As this file type would make this blog even longer, I'm going to jump ahead to what the
EPSG and
UKOOA are doing now in defining the Header records for this specific part of the oil and gas industry.
How the EPSG comes into PlayTurning our eyes to the
EPSG in P
formatted files, we want to enable integrity checking of co-ordinate system definitions in
UKOOA P1, P2, P5 and P6 formats, so a provision is made to describe co-ordinate system by reference to the
European Petroleum Survey Group (EPSG) database of geodetic parameters. This is the group of codes we see in use throughout the
GIS field and in products such as
ESRI and
PROJ.4.
What this allows
UKOOA to do is to
adopt an industry-standard name to be quoted where the geodetic co-ordinate system used is a common system. Defining parameters and units are then as given by
EPSG and are not strictly required to be explicitly given in the P-format records.
As an integrity check, it is considered good practice also to include the explicit definition .The new records which can be used as extensions within the P1/90, P2/94, P5/96 and P6/98 formats are:
H8000 EPSG Geographic CS Name
H8001 EPSG Geographic CS Code
H8002 EPSG Projected CS Name
H8003 EPSG Projected CS Code
H8004 EPSG Vertical CS NameH8005 EPSG Vertical CS Code
H8006 EPSG Database Version
As we know, co-ordinate systems may be two- or three- dimensional.
A vertical co-ordinate system is one-dimensional.
For the P1, P2 and P5 formats:
the H8002, H8003 and H8006 records are required when latitude, longitude, easting and
northing but no height or depth are given;
the H8002, H8003, H8004, H8005 and H8006 records are required when latitude, longitude, easting,
northing and gravity related height or depth are given;
the H8000, H8001, H8002, H8003 and H8006 records are required when latitude, longitude, easting,
northing and ellipsoidal height or depth are given.
For the P6 format, the H8002, H8003 and H8006 records are required.
That is the way
UKOOA and the
EPSG see the offshore world when it comes to positioning and exploration in the North Sea and elsewhere.
Exploration & Production BlogIf you are interested, I also write another blog on the oil and gas industry, mainly describing where exploration is
occurring, the technology being used, history of a region, some geology, etc. and some aspects of the UN Convention on the Law of the Seas.
The blog is located
here.
Enjoy!
