Snorre Marine Operations
Authors: Knudsen J.L. , Lux M.D. , Fines Stein 
Published: October 2008

The Snorre Marine Operations extended over three offshore seasons and comprised about 100 activities.

This paper summarizes the major marine operations and gives a description of the TLP installation. Further it describes the approach taken by the Snorre Project Team in managing these tasks with respect to planning, contracting, organization, verification and training.

INTRODUCTION

Snorre Marine Operations were complex and extended over three offshore seasons, comprising about 100 activities.

This paper describes the major marine operations with focus on the critical installation of the TLP at the Snorre field. In addition to the technical description, the paper covers strategies, plans and measures which contributed to the successful execution of Snorre marine operations. This addresses in particular:thorough concept evaluation,cost-effective solutions on land through early problem identification,effective contracting philosophy,consistent approach to execution from experienced core team with responsibility for all marine operations, andbenefits from extensive training and verification.

MAJOR MARINE OPERATIONS

This section gives an overview of the main marine activities in chronological order of execution, The installation of the TLP itself is discussed in more detail in a separate section.

Deck fabrication

- The integrated deck structure was built across a dry dock at Stord on the west coast of Norway. A major part of the main structure was built in Finland. The load-out and transportation of this 8,000 tonne structure to Norway in April 1990 represented the start of the marine operations of the project.

In order to complete the deck, a total of 22 preassembles and modules were transported to the deck site on barges from various yards and were lifted in by land based cranes.

Substructure fabrication

- The substructure was assembled in Stavanger from 20 sections varying in weight from 300 to 2,500 tonnes, Sixteen of these units were subject to marine transportation, of which 12 came from Taranto in Italy. The transports from lay were made in four trips, two standard barge tows, one barge carried by a heavy-lift ship and one transport where three main sections of columns were loaded directly onto the deck of a heavy-lift ship.

The square bottom pontoon section of the substructure was assembled across a dry-dock. This ring pontoon section was lifted from its support by a submersible barge, "Giant 2", and brought out in deeper water outside the yard. By submerging the barge, the ring pontoon was brought afloat. The erection of the columns was performed by shearlegs lifting the three column sections in each corner.

Upon completion of the substructure construction in August 1991 and before tow to the mating site at Stord, the substructure went through comprehensive submergence tests in the fjord outside Stavanger.

Well template installation

- The TLP well template was installed already in summer 1990 to allow drilling of six wells prior to installation of the platform, After tow from the fabrication yard at the west coast of Norway, the 1,800 tonne TLP well template was installed by the semi-submersible crane vessel (SSCV) "DB1 02".