Richard A. Corbett
Refining/Petrochemical Editor
New assays on two important Norwegian North Sea crude oils, Statfjord and Gullfaks, have updated earlier assays published by OGJ on June 6, 1983.
Both are high-quality, low-sulfur crudes that will yield a full range of good-quality products.
All assay data came from industry-standard test procedures (Table 1).
STATFJORD
The Statfjord field, operated by Statoil the Norwegian state oil company, is the largest in the North Sea. Production started in 1979.
Statfjord is a typical North Sea crude, produced from three separate platforms and three separate loading buoys with interconnecting lines. Current production is about 700,000 b/d.
GOOD QUALITY FRACTIONS
The whole Statfjord crude is lightly paraffinic and low-sulfur.
Quality is similar to Brent Blend, with a slightly lower sulfur content. See Fig. 1 for a TBP distillation curve.
The naphtha cuts are of intermediate to naphthionic quality, and therefore very suitable for gasoline production.
The kerosine cut is of intermediate quality. Its good cold flow and burning properties make it suitable for the production of jet fuel.
The gas oil fraction has low sulfur and good cetane index. It is therefore suitable for diesel and heating oil production.
Straight-run fuel oils are of low viscosity, medium pour point, and have low sulfur and metals contents.
Vacuum residue is sufficiently low in sulfur, making it suitable for low-sulfur fuel oil.
The vacuum gas oil is fairly paraffinic.
That, and its low sulfur content, make it a good catalytic cracking feedstock.
Both atmospheric and vacuum residua are good thermal cracking and visbreaking feedstocks.
GULLFAKS
Gullfaks is produced from a large field in Block 34/10 of the Norwegian sector of the North Sea production area. Statoil operates the field.
Gullfaks is not a typical North Sea crude oil because it is more biodegraded than other crudes from the region. Biodegradation has removed most of the waxy normal paraffins, resulting in a heavier, more naphthionic and aromatic crude.
But sulfur and metals contents are low despite the crude's high density. The crude is very good for gasoline production and produces better product yields than its gravity indicates. See Fig. 2 for TBP curve.
The crude is currently produced from two platforms, with a third coming on stream during 1990. Production from all three platforms will be 500,000 b/d.
GULLFAKS' PROPERTIES
Gullfaks is a medium naphthionic, low-sulfur crude. Naphtha quality is very good for gasoline production, with good octane values of the light and heavy naphthas.
Kerosine will be suitable for production of jet fuel in blends with other, paraffinic crudes. Cold properties are very good. The low-sulfur gas oil also has good cold properties.
Straight-run fuel oils have low pour point and low sulfur and metals contents. Vacuum residue is also relatively low in sulfur, and is therefore good for low-sulfur fuel oil.
LOADING DATA
Statfjord and Gullfaks are both loaded from offshore buoys to dedicated tankers of 110,000 and 130,000 metric tons for direct shipment, or carried to the underground Mongstad terminal (see picture) on the West Coast of Norway. The terminal, owned and operated by Statoil, can handle tankers up to 300,000 DWT.
The following assays on both crudes detail their high-quality properties.
[SEE BOOK FOR STATISTICS]
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