Raude Formation (elevated)
(From NPD Bulletin no. 1)
Statfjord Group
Name
The formation is named after Eirik Raude (Raude = Red), the
Viking discoverer of Greenland.
Well type section
Norwegian well 33/12-2
(Mobil) (Figure 17), from 2790 m (9153 ft) to 2951 m (9681 ft)
below KB.
Well reference section
UK well 211/24-1 (Conoco/Gulf/NCB), Figure 17.
Thickness
In the type well the member is 161 m (528 ft) thick and in
211/24-1 it is 119 m (391 ft).
Lithology
In the type well the basal part of the formation consists of a
'coarsening upward' sequence of grey, green and red-brown silty
claystones, grey arkosic sandstones and white, pink and grey-brown
dolomitic limestones. This basal part of the section is often
difficult to recognise away from the type well and is locally absent.
Above 2905 m (9530 ft) in the type well the member consists of
approximately equal amounts of sandstone and silty shale. These
sandstones are fine to medium grained and poor to moderatley sorted
with subangular grains. They are generally micaceous and have a
kaolinite matrix. The silty shales are grey to light green or
occasionally red-brown in colour, and micromicaceous. Carbonaceous
debris, sometimes in thin laminae, is present but distinct lignite
beds are absent. Away from the type well the sandstone percentage
in this upper part of the formation may vary from about 15 to about 75.
In the area of the Brent and Statfjord Fields the average sandstone
bed thickness is about 2.5 m (8 ft) and shale beds average about
4 m (13 ft) in thickness. Correlation of individual beds from well
to well is virtually impossible. The lithological content and
sedimentary structures in the upper part of the formation, particularly
large scale cross-bedding and scour and fill, are consistent with
deposition in a braided stream environment.
Boundaries
The base of the member is the base of the
Statfjord Group. The change from the more argillaceous Cormorant
Formation sediments to the more sandy Statfjord Group via the
transitional 'coarsening upward' unit is clearly defined on the
gamma ray and sonic logs. The top of the formation is the base of the
first massive sandstone of the overlying more arenaceous formation.
This boundary is normally clearly marked by a change from an
irregular to a more blocky log response, particularly in the gamma
ray log. Individual sandstone beds in the overlying
Eiriksson Formation are more laterally
extensive and the base of the lowest sandstone which is correlatable
between wells will egnerally indicate the top of the Raude Formation.
Distribution
The formation can generally be recognised wherever the
Statfjord Group is well developed.
Teh basal 'coarsening upward' unit is though to have a more limited
distribution but this cannot be defined as many wells terminated in
or just above this basal unit.
Age
Rhaetian. The top of the formation may approximate to the
Rhaetian-Lower Jurassic boundary in the type well but is probably
older to the west (Figure 18).
