Norne-Heidrun: Closing "The Loop" With Diverless Flanged Connections

Abstract Subsea completions in deep waters are becoming more and more frequent around the world. This entails the use of innovative technology, remote interventions but, of course, also a constant attention to cost effectiveness to make any possible development a viable one. As a result of these continuous efforts towards new solutions, Statoil decided in 1999 to focus their attention on the possibility of using flanges as remote connection system. The idea originated from two basic concepts:Flanges have been widely used in the past within the offshore industry, therefore they have got a large track record and are standardized equipment (e.g. ANSI or API);Procurement cost for flanges is low when compared to other type of connectors. Sonsub proposed to Statoil the use of their newly developed Brutus system as part of the new development in the Norne-Heidrun area. Brutus is a tie-in system capable to tie-in rigid pipeline up to 16" and with minor modification could reach up to 24"; larger sizes are strictly dependent upon specific scenario requirements. It was Statoil's intention to connect the Norne FPSO to Heidrun TLP and to the 42" Åsgard Transport system through a 16" piggable pipeline system called "The Loop". With this respect Sonsub were awarded an EPCI contract for the design, fabrication and installation of two subsea manifolds, tie-in spools and relevant protection covers, two In-Line tee protection covers and the installation of the flexible riser to Norne FPSO. The offshore campaign took place in the last quarter of 2000. This paper presents the project, briefly describe the Brutus system capabilities and give all information on how the operations for "closing" the Norne-Heidrun U-Loop were completed. Introduction The objective of the project is to connect two production facilities operated by Statoil on the North Sea (Norne FPSO and Heidrun TLP) with a 16" piggable pipeline system (called "The Loop") in order to export the produced gas towards the 42" Åsgard Transport System. Norne Heidrun Subsea Structure and Tie-in is the name of the project that in September 1999 Statoil decided to award to Sonsub. Statoil specifically decided to trust the use of flanges and gave Sonsub the go ahead on the basis of a competitive economical proposal, which showed that the avoidance of mechanical connectors is in itself a major saving. This is an EPCI contract which has seen Sonsub for the first time as main contractor for such kind of work, and it has been carried out in co-operation with Saipem and Sasp Offshore Engineering involved in the installation analysis and engineering respectively. The scope of work includes the Engineering, Fabrication, Testing and Installation of the following subsea structures:Norne Export Riser Base;U-Loop Manifold;Norne and Heidrun In-Line Tees Protection Covers;Norne Expansion Spool, Heidrun Expansion Spool and Åsgard Crossover Spool;GRP Protection covers for the three spools;Subsea Pig Launcher;Blind Flange Removal Tool.