Marginal Field Development In Mature Areas Of The North Sea

Abstract

ABSTRACT In the North Sea a comprehensive infrastructure of production, installations and pipelines have been installed in the last 20 years. As the existing oil and gas fields start to decline, it is cost effective to use the spare capacity on these existing production installations for marginal fields. To ensure economy in the marginal field development the facilities on the outlying fields must be reduced to a minimum. The facilities needed are very dependant on the product being processed and the distance to the existing production installation. However, experience has shown that the modifications necessary on the existing installations can be extensive, difficult to estimate and normally has had significant cost escalation. This paper will outline the North Sea infrastructure, indicate the types of minimum facilities and installations used on the satellite fields, and briefly discuss the problems with modifications on existing installations. EXISTING INSTALLATIONS IN THE NORWEGIAN NORTH SEA The major production installations in the Norwegian North Sea are grouped in five areas;Ekofisk area (Southern North Sea)Sleipner area (Southern North Sea)Frigg area (Mid North Sea)Oseberg (Mid North Sea)Statfjord/Gullfaks area (Northern North Sea). Most of these areas are connected to a gas pipeline system which either exports to the Continent or Great Britain, Very little gas is used in Norway and therefore nearly 100% is exported. There have been built or are under planning three large diameter pipeline systems to the Continent and two pipelines to Great Britain, the total capacity is over 200 MSm3/Day. Because of the long distance to the Continent the southern pipeline systems used are dry gas systems and therefore the gas can be delivered to the market without further processing. The Frigg systems is a semi dry system with limited processing on land. However, the system from Statfjord/Gullfaks is a wet system, the gas being processed on land in Norway before transfer to the southern gas systems. This gas infrastructure has dictated the process systems required on the platforms located in the different areas. In the Ekofisk/Sleipner areas the gas system is a dry/sales gas system. Therefore the liquid products are unstable and the N.G.L. products are transported with the oil products to land for further processing, In the Oseberg/Statfjord/Gullfaks area the liquids produced are stabile, therefore the gas export will be a rich gas and must have the N.G.L. removed before transfer to the southern gas systems. Export from the Frigg area is special as the gas from the reservoir is very dry and needs very little processing. Gas from the fbture Troll field will be transported untreated to Norway for processing before transfer to the dry export system. This project is the largest example of mukiphase flow over long distances and deep water in the Norwegian North Sea.