Design, Installation, And Connection Of Subsea Lines On East Frigg Field

ABSTRACT This paper describes the subsea network which interconnects the three subsea templates at EAST FRIGG field, and connects this field to the FRIGG field, 18 kilometers away. The design requirements and main characteristics of the network are summarized and the particular features related to the fabrication and offshore installation of the infield sealine bundles are outlined. The bundles - which consist of a carrier pipe including production and service lines - are built onshore in one length and will be towed out, pulled and connected to the subsea manifolds. A description of dedicated subsea tools which have been engineered and fabricated in order to ensure a diverless installation of these bundles is given. Some specific features have been implemented during design and fabrication of the subsea electrical cables and umbilical. These features, which are further described, will allow for installation and connection of these lines without any diver assistance. Finally, the particular role of the Remote Operated Vehicles which provides a back-up solution on many occasions is outlined. INTRODUCTION The EAST FRIGG field consists of two small and separate gas reservoirs as described in OTC 5765. The produced gas from the wells located on two Production Stations is commingled in a Central Manifold Station and piped to FRIGG field for treatment. In addition, the control of the EAST FRIGG subsea installations is ensured from the FRIGG installations. The subsea network interconnecting the EAST FRIGG and FRIGG fields has to meet a high level of reliability so that the production level is as specified during the 14 years lifetime of the field. The design of this subsea network is based upon a diverless offshore installation as this will be an economical way of developing marginal fields in even greater water depth. GENERAL REQUIREMENTS The subsea network is designed to fulfil the following requirements:transport the produced gas from the two EAST FRIGG Production Stations to FRIGG TCP2 platform. The design pressure is 170 bar for a production of 4 million standard cubic meters per day. A detailed description of the Subsea Stations is given in OTC 5766.provide facilities to kill any of the production well remotely, from the Central Manifold Station.provide necessary high/very high pressure hydraulic fluids to activate the subsea valves on the Production Stations.provide necessary electrical power and transmit signals to the Production Stations so as to operate remotely, from FRIGG field, both Stations. The control system is detailed in OTC 5767.provide facilities for injecting methanol and corrosion inhibitor at the subsea Xmas trees to prevent hydrate formation in the pipeline. Furthermore, as the production life of the field is 14 years, reliability is an important factor which was considered in the various design phases.