A new type combined pull-in and connection system has been developed for the Troll Oil field Development in the North Sea.

At Troll Oil, satellite wells are spread out in a wide area and tied back to the floating production unit by flexible flowlines and umbilicals via manifolds and a riser base. For the 1st phase of the development more than 120 diverless tie-ins of flowlines and umbilicals are required, 2nd phase will require an additional 150 tie-ins. All pull-in and connection operations will be made diverless at a waterdepth of 325m (1OOO ft).

To perform these tie-in operations in an efficient manner the need for a new tie-in system was required.

The tie-in tool PICT is based on subsea pull-in wire establishment, horizontal pull-in and a hinged clamp connector. The system is made to be flexible related to laying method, installation sequence and reversability. This tie-in system represent a new generation of tools which can be further developed for very deep waters.

This paper present the Troll Oil tie-in system and what considerations were made to make the system optimal related to cost and operability.

Troll Oil Field Development

The Troll field is one of the largest gas fields offshore in the world, located near the west coast of Norway at a depth of 325 m (1000 ft). Below the gas there is a thin oil layer. By using horizontal drilling this oil can be developed. The gas in the field is sold and is under development. To produce the oil the gas pressure is required. Troll Oil project had to be developed fast and with a lot of wells spread out in a wide area.

The subsea production system consists of single well satelites tied back to 6 or 8 slots manifolds with gathering lines via a riser base to a floating production unit (FPU). Between the satelites and the manifolds there are one 6" or 8" flexible flowline and one steel tube integrated service umbilical (ISU). Between the manifold and the FPU there are 2 × 9" or 2 × 10" flexible gathering lines and one main ISU. All gathering lines are connected at the riser base to dynamic risers.

Troll Oil Tie-in System Development Schedule

The design of a combined pull-in and connection tool started back in 1991 based on the experience gained on the Troll Oseberg Gas Injection Project (TOGI). Late 1992 basic engineering studies were performed at Troll Oil for the operator Norsk Hydro as. Summer 1992 the tie-in contract were set out. Testing of the first Pull-in and Connection Tools (PICT) started summer 1993 which were followed up by system testing tie-ins at the Production Riser Base, Manifold Centers and the Sattelites/Permanent Guide Bases. Summer 1994, first tie-in operations offshore will be performed. Production start up of the field is scheduled for january 1st 1996.

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