Nansen Formation (elevated)
(From NPD Bulletin no. 1)
Statfjord Group
Name
After the Norwegian polar scientist, explorer and statesman,
Fridtjof Nansen.
Well type section
UK well 211/24-1 (Conoco/Gulf/NCB) (Figure 17) from 3112 m (10,209 ft) to
3158 m (10,361 ft) below KB.
Well reference section
Norwegian well 33/12-2
(Mobil), Figure 17.
Thickness
46 m (152 ft) in the type well and 19 m (59 ft) in the reference well.
Lithology
In the type well the formation consists of medium- to coarse-grained,
fairly well sorted, homogeneous, white sandstones with a calcite
cement and a subordinate kaolinite matrix. Occasional horizons with
granules or pebbles are present. Carbonaceous material and mica are
rare but glauconite is quite common. Thin shale beds containing marine
fossils are present.
At the top of the formation, from 3112 m (10,209 ft) to 3135 m
(10,283 ft) in the type well is a more prominent calcareous horizon
defined informally as the calcareous sandstone bed. This may grade
locally into a sandy limestone, for example, in the Brent Field.
The Nansen Member thins towards the east and passes laterally into
calcareous siltstones and shales in the Norwegian sector (Figure 17).
Although these siltstones and shales are lateral equivalents of the
Nansen Formation they are placed in the overlying
Dunlin Group on lithological grounds.
Boundaries
The lower boundary is marked by the change from the non-calcareous
sandstones of the Eiriksson Formation to
the cleaner, generally calcareous sandstones of the Nansen Formation.
The upper boundary is marked by the change from calcareous sandstone
to the argillaceous sediments of the Dunlin
Group. Both boundaries are well marked on gamma ray and sonic logs
particularly in the UK sector where the member is best developed.
The calcareous sandstone bed at the top of the member is normally
reflected by a distinctive sonic log response (Figure 17). However
as this passes laterally into calcareous siltstones and shales the
sonic log still responds to the calcareous nature of the sediments.
Distribution
The formation is well developed in the Brent Field area. The lower
part of the member overlaps westwards to the Cormorant Field area
where it is probably the only representative of the
Statfjord Group. The calcareous sandstone
bed at the top does not extend as far west as the lower part of the
formation.
Age
Probably Hettangian to Early Sinemurian.
