U.K. NORTH SEA'S FORTIES BLEND CRUDE ASSAYED

Jan. 23, 1995
Anne K. Rhodes Refining/Petrochemical Editor Forties Blend is an important crude comprising oil and gas liquids from 20 fields in the central North Sea (Fig. 1) (29975 bytes) . This assay of the 400 API, 0.35 wt % sulfur crude was performed in late 1993. According to the Journal's latest production survey, average 1993 production of Forties Blend was 427,750 b/d. Enterprise Oil says current production is about 400,000 b/d.

Anne K. Rhodes
Refining/Petrochemical Editor

Forties Blend is an important crude comprising oil and gas liquids from 20 fields in the central North Sea (Fig. 1) (29975 bytes). This assay of the 400 API, 0.35 wt % sulfur crude was performed in late 1993.

According to the Journal's latest production survey, average 1993 production of Forties Blend was 427,750 b/d. Enterprise Oil says current production is about 400,000 b/d.

Since an assay of Forties Blend was last published in the journal, several fields have been added to the system: Everest, Lomond, Bruce, Tiffany, Toni, Nelson, and East Brae (OGJ, July 15, 1991, p. 53). The API gravity of the crude has increased almost 20, while its pour point has increased from - 2100 C. to - 1200 C.

Since participants in the Forties system have invested some 600 million-both onshore and offshore-in recent years, the pipeline system now has a nominal capacity of 1 million b/d.

The crudes are commingled at the Forties C and BP Unity platforms and transported via 164 km of 36-in. pipeline to landfall at Cruden Bay on the northeast coast of Scotland. The 36-in. main pipeline ties into Forties C at the five platforms of BP's Forties oil field.

Marathon's South, Central, North, and East Brae fields are linked to Forties C via a 120-km, 30-in. diameter pipeline from South Brae, on which there are three subsea tie-in points. And Elf's Heimdal field in the Norwegian sector of the North Sea ties into the Brae pipeline via a 117-km, 8-in. line.

Other fields comprising Forties include:

  • Amoco (U.K.) Exploration Co.'s Montrose and Arbroath fields, which are linked to Forties C via a 46-km, 14-in. pipeline.

  • Sun Oil Britain Ltd.'s Balmoral, Glamis, and Stirling fields, which tie into the Brae line via a 14-km, 40-in. line.

  • BP's Buchan field, which is linked to Forties C via a 54-km, 12-in. line.

  • BP's Miller field, which is linked to South Brae through an 8-km, 18-in. line.

  • Agip (U.K.) Ltd.'s Tiffany and Toni fields, which are tied into the Brae pipeline via a 4-km, 12-in. line.

Tied into the 5-km, 36-in. main pipeline between Forties C and the BP Unity platform-installed in 1992-are Amoco's Everest and Lomond fields, linked via a 63-km, 14-in. line. BP's Bruce field is linked to Unity via a 248-km, 24-in. pipeline, and Amerada Hess Ltd.'s Scott field, via a 76-km, 24-in. line. Enterprise's Nelson field, added to Forties Blend in February 1994, is linked to Unity via a 25-km, 20-in. line.

The Unity platform is equipped for the addition of as many as five more risers in the future.

Total operates gas processing facilities at St. Fergus, where a terminal sends gas liquids to Cruden Bay through a 12-in., 25-km, buried pipeline, to join the main pipeline. Mobil Oil Co. Ltd.'s SAGE terminal also is connected to the St. Fergus-Cruden Bay line.

From Cruden Bay, a 209-km, 36-in., buried pipeline takes the crude to the stabilization, separation, and processing facilities at the Kerse of Kinneil. At Kinneil, a two-stage heating and separation process produces stabilized crude and raw gas. The plant comprises three trains that can process as much as 1 million b/d of pipeline liquids (Fig. 2) (11400 bytes).

More than 7,000 metric tons/day of raw gas can be processed at Kinneil. In these facilities, gas is compressed and passed through a de-ethanizer, which produces dry gas (methane and ethane). The dry gas is treated to remove H2S and CO2, then used as fuel at BP's refinery at Grangemouth, Scotland. BP Chemicals uses any remaining dry gas as chemical feedstock at its Grangemouth petrochemical complex.

The remaining gas is depropanized and debutanized to produce propane, butane, and condensate. At the Grangemouth docks, there is refrigerated and pressure storage for propane (10,300 metric tons) and butane (9,700 metric tons), plus condensate storage, export and tanker-loading facilities, and berthing. BP Chemicals also uses gas products within the Grangemouth complex.

The Forties Blend crude is pumped through a 19-km, 30-in., buried pipeline to the Dalmeny storage facilities, and to the Grangemouth refinery. The Dalmeny tank farm's eight tanks have a total capacity of about 4 million bbl.

Product is shipped to two crude oil loading jetties at Hound Point terminal in the Firth of Forth via 48 and 40-in. loading pipelines and ballast lines. One jetty handles vessels up to 150,000 dwt and the other, vessels up to 300,000 dwt. Loading and deballasting can be carried out at a rate as high as 15,000 metric tons/hr.

Pipelines between Hound Point and Dalmeny transfer ballast water from ships to Dalmeny. The water is purified, then discharged into the River Forth.

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