Fram Vest project - Subsea tie-back to a floating production unit
Authors: Hjermann Bjørn Kvaal 
Published: October 2008

This paper describes how marginal reserves in the North Sea can be exploited by utilizing existing infrastructure and processing capacity. During modification of the existing floating production unit (Troll C), shutdown was kept to a minimum. Flexible risers were installed between "hot" Troll risers. A spectacular floater-to-floater module lifting operation was carried out, and a 13%Cr multiphase flowline with modified corrosion protection system was developed, tested and successfully installed. System design provides flexibility for potential future installations. The Fram Vest Project was completed on schedule and well below budget.

Introduction

Fram Vest is a marginal oil field some 120 km off the coast of Norway in the North Sea, about 20 km north of the Troll C floating production unit (ref Fig. 1). The water depth is 360 meters. Recoverable reserves did not justify a stand-alone development. This paper describes how Fram Vest is tied back to the Troll C floating production unit, utilizing existing process capacity and the pipeline infrastructure in the Troll area. The paper focuses on the main technical challenges, marine operations, and commercial agreements.

Fig. 1. Fram Vest Location (Available in full paper)

The concept consists of subsea templates enabling wellstream production and gas injection. A total of four oil producers (one multi-lateral) and one gas injector have been drilled. The wellstream is routed through a flowline to Troll C for processing. Gas for injection is transported from Troll C to Fram Vest through a gas flowline. Well control is provided through an integrated service umbilical from Troll C (ref. Fig. 2).

A major success factor for the project was the minimum disturbance of Troll C operations during modification and start-up of Fram Vest. The Fram Vest module comprised of inlet separation, gas injection and metering facilities. The investment budget was NOK 4.3 billion, the final cost was about 15% lower.

The remaining resource base in PL090 is similar in volume to Fram Vest, but is distributed in several different reservoirs. This may be developed later and in various stages to the Fram Vest subsea system.

Fig. 2. Fram Vest subsea system (Available in full paper)

History

The licence was issued in 1984. In 1995, Hydro bought 15% from Mobil and became operator of the licence PL090. The owners are:Hydro (25%)ExxonMobil (25%)Statoil (20%)Gas de France (15%)Idemitsu (15%) Two exploration wells were drilled in 1996-1997. The plan for development and operation was accepted by the Norwegian government in March 2001, and oil production commenced October 1, 2003.

Reserves and production strategy

Estimated in-place resources on Fram Vest are 42 MSm3 of oil and 12 GSm3 of gas. Estimated recoverable reserves are 17 MSm3 of oil and 8 GSm3 of gas. The drive mechanism is gas injection for approximately 6 years followed by pressure depletion for the rest of the lifetime. The economic evaluation is based on 16 MSm3 of oil and 3.5 GSm3 of gas, assuming shutdown of Troll C in 2016. The expected production profile is given in Fig. 3. Oil production started up October 1, 2003.