Subsea Developments on the Statfjord and Sleipner Satellite Fields: Project Execution, Testing, Start-up
Authors: Bjørnebekk Svein 
Published: October 2008

The world's largest subsea contract was launched in April 1991 for Statoil's Statijord satellite project - SSP - and initially included subsea production equipment for the two satellite fields, Statijord Nord (North) and Statijord Ø st (East). The project was later made responsible for subsea units to two satellite installations connected to the Sleipner A facilities. This involves six and two templates, hooked up to the Statfjord C and Sleipner A platforms, respectively, totalling 25 Xmas trees. The SSP is Statoil's third subsea development, following Gullfaks (1986) and Tommeliten (1988). The two Statijord satellites are located near the Statijord, Gullfaks and Snore fields, about 200 km west of Bergen, while the Sleipner field is located west of Stavanger close to the boundary with the UK North Sea. The two Statijord fields are primarily oil producers with production start in the fourth quarter of 1994 from Statijord East and in 199396 from the North field. The subsea installations were ready in the summer season of 1993, with drilling and completion following. Sleipner is a gas field and the production from the subsea installations became essential to ensure gas delivery to the European gas network on I October 1993. The paper will describe the technology applied and the main elements relating to both onshore and offshore executions. Finally, it will address the way these installations have brought Statoil closer to a standardised solution for subsea developments.

STATFJORD SATELLITES

Statfjord North is located 17 km from the Statfjord C platform in 300 metres water, while Statfjord East is seven km away in 200 metres of water. Completed in 1990, conceptual design for the SSP aimed to meet the following main requirements:versatility and flexibilityfailure tolerantstep-by-step development of the two fieldslow investment and operating costdiverless installation, maintenance and repairsimultaneous operations, such as drilling while performing pull-in of flowline or umbilicalseparate and independent retrieval of all production modulesremote intervention from monohull vesselsintroduction of a standardised subsea system.

The two fields are configured in a similar way, see fig.1. Each utilises two production templates supporting three Xmas trees apiece, plus a water injection template. The production flowline forms a ring configuration, giving flexibility during production in failure cases and permitting round-trip pigging. Flowlines consist of hard piping with about 300 metres of flexibles for tie-in to the templates and the platform. Flexibles are also used between the templates. The umbilicals are also installed in a ring configuration for redundancy purposes, with a branch to the water injection template. These umbilicals will supply both electrical and hydraulic power as well as scale and corrosion inhibitors. Methanol will be provided in a separate 2.5 inch pipeline. The Xmas tree is a conventional five by two inch design for 5 000 psi, and will be hooked up to its branch line through a choke bridge unit. Retrieving only these units provides access for retrieving the manifold unit, if required. Well killing will therefore be unnecessary since the Xmas trees will remain in place.