Frigg Decommissioning - HSE
Authors: Tveteras Bjorn Oscar 
Published: May 2011

The decommissioning of large North Sea platforms gives rise to significant HSE challenges. These include a high level of work activity, numerous lifting operations and work in exposed area, all of which take place on a platform where the layout rapidly changes from day to day. Hazardous material, like asbestos, scale and mercury need to be removed and must be handled in a safe manner. In some areas, such as the protection against toxic fumes when hot cutting painted steel, better knowledge and methods had to be developed and implemented.

Strong management of the work with control measures, safety initiatives and training of personnel was essential throughout the various phases of the project to keep control over occupational risks.

The safety statistics show no fatality or severe accidents but a rather high number of small injuries. Some of the high potential incidents were not related to demolition work but infrastructure and support function.

Details of the " material account?? including hazardous waste, reused and recycled material, and energy consumption in terms of CO2 emission per recycled ton of steel, are shown.

Introduction

The Frigg & MCP01 Cessation Project (FCP) is the largest decommissioning project undertaken in recent years and includes removal of six topsides, three steel jackets and sealines with a final disposed-of weight of 87,000 metric tonnes. Different methods have been applied from single and module based lifts to "piece small" dismantling and removal.

The Frigg Field was a gas field, situated in the North Sea, on the border between Norway and United Kingdom (UK).

The field was developed with three installations located in the Norwegian sector, a drilling and production platform (DP2), a treatment and compression platform (TCP2) and an unused steel substructure damaged during installation in 1974 (DP1). Three other installations were located in the UK sector, a treatment platform (TP1), a concrete drilling platform (CDP1) and a living quarters platform (QP). The platforms were installed in the period 1974 to 1977. The produced gas was transported to St Fergus in Scotland, through the Frigg pipeline, passing through a manifold and compression platform (MCP01) situated at the mid-point of the pipeline. The partners for the Frigg Unit Installations are Total E&P Norge AS 28.66%, Statoil ASA 32.16%, and Total E&P UK Limited 39.18%.

The Frigg Field production was shut down in 2004 with decommissioning starting in 2005 after cleaning of the process equipment/utilities and removal of most loose hazardous wastes. This paper does not address the cleaning process.

The Frigg Field was the first large field to be fully shut-down and decommissioned in the Norwegian sector of the North Sea.

Three Frigg Field substructures (TCP2, TP1 and CDP1) were made of concrete while the other three substructures were steel jackets. MCP01 were also made with a concrete substructure. None of the substructures have been used for storing crude oil. The concrete substructures were not designed and built for removal, and the assessment of the alternatives for removal and onshore disposal, or partial removal through cutting of the substructure, revealed too high a risk and uncertainty.

In accordance with the 1992 OSPAR Convention and the OSPAR Decision 98/3 on the Disposal of Disused Offshore Installations after a derogation process permits were issued allowing the concrete substructures to be left in place after removal of all the external steelwork.