Snorre, North Sea Central, Norway

The Snorre field lies in blocks 34/4 and 34/7, approximately 200km west of Floro, in Norway. Block 34/4 was awarded in 1979, while block 34/7 was awarded in 1984.

RESERVOIR

The Snorre reserves lie in the fluvial sands of the Lunde formation from the late Triassic period and the Statfjord formation is early Jurassic.

RESERVES

Estimates of proven and probable oil reserves have shown a positive trend, which has risen by almost 84 per cent since the plan for development and operation was first presented in 1987. Snorre has recoverable reserves of 1.4 billion barrels of oil, 6 billion m³ of gas and 6 million tonnes of natural gas liquids.

The original plan for Snorre put daily oil production capacity at roughly 186,305 barrels. This was upgraded in 1997 to 245,000 barrels, with a further 115,000 barrels added when the process module for the Vigdis crude was installed, giving a daily capacity of 360,000 barrels/day.

Field life is expected to extend into the year 2020.

RECOVERY OF OIL AND GAS

The drive mechanism is based on water alternating gas injection (WAG) down-flank, in the entire Statfjord formation. It is estimated that 41 per cent of the stock tank oil originally in place in the field can be produced.

PHASE 1

Plans called for Snorre to be developed in two phases. The first concentrated on the southern part of the field, in which 150 million m³ of recoverable oil reserves are located. Production facilities comprise a steel tension-leg platform (TLP) on the southern part of the field and a subsea production system tied back to the TLP. Phase one of the Snorre development is based on 46 oil wells - 36 drilled from the TLP (six predrilled and the other 30 drilled during production) and another ten at the subsea station.

Moored to the seabed by 16 steel tethers, 32in in diameter, stabbed into four 5,700t concrete foundation templates, the platform is an integrated production, drilling and quarters installation.

The 30,000t steel hull was fabricated by Kvaerner Rosenberg and the subcontractor Belleli. It was mated to the 30,000t steel deck built by Aker Stord. Installation was assisted by the M700 crane barge and installed by Rockwater.

Located at a depth of 335m, the 2,400t subsea production system was lifted by Saipem's M7000 crane vessel in a tandem lift. The guidelineless system allows six oil wells and four water injectors to produce up to 60,000 barrels/day. Snorre A came on-stream in August 1992.

PHASE TWO

Phase two of the development embraces the field's northern flank, which will be developed with a four-column semi-submersible platform (Snorre B) with drilling, processing and accommodation facilities, as well as a subsea production system. The Northern flank is thought to contain up to 25% of the field's recoverable oil.

Snorre B came on stream in June 2001 from well C-5, sending fully-processed crude through a 45km pipeline to Statfjord B for storage and transport. Two further wells were then brought on stream, bringing production up to an expected level of 70,000 barrels per day. Associated gas will be injected into the reservoir or piped via the Snorre tension leg platform to the Statpipe system.

Snorre B is expected to produce 113,000 barrels per day at peak. In addition to the Snorre B development, new technical resources will be phased in where oil has already been proven.

An estimated 362 million barrels of oil remains to be recovered from Snorre B. New wells will be drilled to clarify whether additional recoverable oil is present in the area.