Ekofisk Observed Weather Compared With Weather Predictions
Authors: Hjorteland Kjartan , Mes Marius J. , Magnusson Anne Karin 
Published: October 2008

Abstract
Phillips Petroleum Company Norway (PPCoN) is the operator of the Ekofisk oil field, located in the middle of the North Sea. PPCoN operates this oil field on behalf of the Phillips Norway Group. For our Ekofisk eXtreme Wave Warning System (EXWW) as well as for our offshore operations we need 12, 24 and 48 hour as well as day 2, 4, 5 and 6 weather and oceanographic forecasts of as good a reliability as is reasonably possible. PPCoN contracted Det Norske Meteorologiske Institutt (DNMI) in Bergen to provide PPCoN with such special purpose Ekofisk forecasts twice daily. We have compared the measured Ekofisk weather and oceanographic parameters to the predicted conditions. The paper documents the differences and provides statistical evaluations of the uncertainty of the predictions for the late winter and early spring Ekofisk weather of 1998. In addition statistics on predictions given for the most severe Ekofisk storm recorded as part of our Extreme Wave Warning System are presented.

Introduction
Ekofisk is an oil and gas field in the southern portion of the Norwegian North Sea, operated by Phillips Petroleum Company Norway (Phillips) on behalf of the Phillips Norway Group. The field came on stream in 1971. After the subsidence phenomenon was confirmed in 1984, safety considerations for our personnel during severe storms became the prime motivation for the drive to obtain reliable weather predictions. In case of expected wave damage to the subsided structures we also wanted to know when wave damage might be expected to our old platforms, so we could shut down production for a few hours at the height of such a very severe storm. The seabed subsidence, new more stringent safety regulations and higher operating costs resulting from labor intensive technologies of the seventies prompted the installation of two new platforms, which now form the so-called Ekofisk II platforms. These new platforms took over all essential production functions from the older Ekofisk platforms (now called the Ekofisk 1 platforms). These new platforms are designed to operate in conditions including "100 year" design storms. Because the older mostly unmanned platforms still are in place, we continue to need a reliable weather warning system in case weather related damage to these old platforms could possibly occur and to guarantee the safety of our personnel when they make their maintenance rounds.
Phillips started to develop the EXWW system together with DNMI (the Norwegian Meteorological Institute) to provide an early weather warning system. The purpose of this warning system was to establish safe and practical procedures on when to restrict personnel access to platforms, when to remove personnel from certain Ekofisk 1 platforms. With forecasts reliable to over 6 to 12 hours in advance we can properly plan for personnel transfers from outlying platforms. DNMI and Phillips practice exercises on possible extreme situations annually, usually at the start of the storm season in September.
We have bi-annual evaluations of the way severe storms were predicted over the previous few months. These evaluations provide us with spot checks on what the prediction possibilities are, it also gives an opportunity for weather prediction personnel to interact with our platform safety and operations personnel in an office type environment.