1065 - OGP Surveying and Positioning Committee

_____________________________________________________________________________________________________________________Page 42. WHAT HAS HAPPENED AND WHYCo-ordinates describing a position on the earth are only unambiguous if the co-ordinatesystem to which they are referenced is identified. Geographical co-ordinate systemcomponents are geodetic datum and ellipsoid. Projected co-ordinate systems areGeographical Co-ordinate Systems with a projection transformation applied. See annex F foran overview of co-ordinate systems and annex G for a glossary of terms.Petroleum licence boundary co-ordinates have previously been referenced to “EuropeanDatum”. This term is not a precise one. Several versions of European Datum (ED) exist.Generally, in UKCS petroleum operations ED has been assumed to be the first (1950)iteration of European Datum (ED50). This was originally published to unify the co-ordinatesystems used in mainland Western Europe and its extrapolation offshore becomesincreasingly ambiguous as distance from the reference points used in its calculationincreases. In the North Sea these ambiguities are of scientific curiosity only and notsignificant to petroleum operations. However, to the West of Shetland and even further west,differences arising from different technical assumptions quickly become very large.Potentially, tens or even hundreds of metres could be in dispute and could be legitimatelyargued by opposing sides in a unitisation case. For a discovery of oil & gas, such a variancecould have severe economic impact.It is this ambiguity and uncertainty in position that the DTI has removed in the Gazette noticeby defining explicitly what it means by the term "European Datum".2.1 Longitude 6°W (ED50) - the Thunderer LineThe DTI has chosen to be pragmatic in its implementation of these clarifications. Where theambiguity in the term European Datum is small, which happily coincides with areas of matureUKCS petroleum activity, the co-ordinate system in use by the majority of the industry hasbeen adopted. Where the differences in the interpretation of European Datum are potentiallysignificant, a system has been adopted that can be considered to be coincident with the coordinatesystem used by satellite navigation GPS (Global Positioning System). A dividing linehas been chosen (Longitude 6°W in ED50 terms) which is coincident with a UTM zoneboundary. This dividing line has been dubbed “the Thunderer Line”.Co-ordinate Systemsfor Petroleum Explorationand Production Licence Descriptions6 o WETRF89UTM zone boundaryInternational boundary agreedLimit of UKCS designated areaNationalGridED50ED50NationalGridETRF896 o WUKCS licenced areas at February1998____________________________________________________________________________________________UKOOA Guidance Notes on use of co-ordinate systems in data management on the UKCS. November 1999