Abstract

After stressing the importance of marginal field developments, especially in the North Sea, the paper describes a new concept based on innovative technologies.

The concept makes use of the multiphase pumping technology recently developed by the oil industry, combined with a small floating support and retrievable flexible lines.

After describing the technical aspects of the system, the paper gives its main advantages compared to traditional development schemes.

A preliminary economical analysis, based on field data, clearly shows the areas of application and the benefit for the oil operator.

The paper concludes on the potential interest of the system to North Sea fields.

Introduction

Discoveries of large fields in mature offshore basins are increasingly rare. At the same time, a number of small discoveries are still unproduced, having been shelved in the past, because of more attractive fields to develop. Existing production and transportation infrastructures, fairly often on the decline, offer the means of making the development of these discoveries profitable, provided that innovative technologies and new associative structure at the financial level are implemented.

To develop these discoveries, the operators have at present several alternative schemes:

  • Conventional developments, using one or more fixed platforms (in steel or concrete). These developments are no longer comparable with the earlier ones. Theyhave been improved significantly by the use of lighter equipments and structures, and they are increasingly associated with the use of subsea wellheads.

  • Floating production facilities, generally consisting of tension leg platforms, semi-submersibles combined with subsea wellheads, F.P.S.O. or production ships.

  • Satellite developments, in which the field is connected to an existing neighbourg platform. Two forms of satellite developments are observed:

* with subsea wellheads, the effluent being flowed to the existing installations throughout a multiphase pipeline by natural pressure drive,

* with a light unmanned platform where a preliminary separation of phases may be done before sending them to the host platform.

We can note also the appearance in North Sea of nomadic production ships, such as the Petrojarl in Norwegian waters and the Seillean, operated by BP, in the British zone.

The biggest fields are developed by conventional methods. Satellite developments concerns small fields, less than 45 Mboe average size, and their use is limited by the distance that the effluent can travel with natural pressure of the reservoir. For oil, the present record is about 15 km (Don field), and the average connecting distance for projects under way or probable, is 8 km.

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