Ran sandstone units (new) (Ransandsteinsenhetene)
(From NPD Bulletin no. 5)
Recommended as Member in Norlex
Cromer Knoll Group
Name
Ran was the wife of the sea god Gir in Norse mythology. She liked to
drag sailors down to the depths with her net.
Well reference sections
Norwegian well 2/7-15
from 3498 to 3450 m, coordinates N 56°23'46.82", E 03°18'54.63" (Fig. 22). 16 m of cores in the lowermost part of the formation.
Norwegian well 7/3-1
from 2412 to 2396 m, coordinates N 57°50'35.25", E 02°44'55.61" (Fig. 23). No cores.
Norwegian well 17/11-2
from 1802 to 1767 m, coordinates N 58°06'54.9", E 03°22'09.8" (Fig. 13). No cores.
Thickness
The gross sandstone thicknesses vary from a few metres up to approximately
100 m. The gross thicknesses in the reference wells are 48 m (2/7-15), 16 m (7/3-1) and 35 m (17/11-2). Up to 130 m (gross) of Aptian-Albian sandstone sequences are penetrated in block 16/27 in the UK sector (see Distribution).
Lithology
The colour of the sandstones ranges from white to light grey, green and brown to reddish-brown. The sandstones are generally argillaceous, sometimes calcareous and glauconitic, and usually do not represent potential reservoir rocks in these wells.
Basal stratotype
The various sandstone units may appear in contact with the
Åsgard, Tuxen,
Sola and Rødby
Formations (Figs. 4,7,8 and 9). Their lower boundaries are generally defined
as the base of an upward decrease in the gamma-ray response when passing
into the sandstone units (Figs. 22 and 23). The gamma-ray readings in the
calcareous marlstones and chalks of the Tuxen Formation, especially its
upper part, and the Mime Formation may be similar to
those in the sandstones. The velocity curve is often less suitable, for
defining the lower boundary.
Characteristics of the upper boundary
The upper boundary can usually be identified as an upward increase in
the gamma-ray readings (Fig. 22) and generally by a slight decrease in
the sonic velocity.
Distribution
The Ran sandstone units are encountered in only a few
wells in the Norwegian sector (Fig. 21 and Remarks).
Occurrences of formation tops in wells
Age
Ryazanian-Albian.
Depositional environment
The sandstones that have been penetrated are described as shallow (Norwegian sector) and deep water (UK sector) submarine fans.
Remarks
Hesjedal & Hamar (1983) recognised several scattered sandstone sequences
which they described as the Kopervik and Klepp Formations in the Central
Trough and Norwegian-Danish Basin, and the Florø Formation in the Agat
Field in blocks 35/3 and 36/1. The Kopervik and Klepp Formations are here
described as the Ran sandstone units. Since they consisted of several
isolated sandstone bodies they should not have been given formation status,
and the names did not conform with the existing recommendations. The Florø
Formation is formally defined as the Agat
Formation in this paper (see also General litho-stratigraphic notes for Cretaceous).
In the UK sector (the Andrew Field), just south of the Andrew Ridge and
Fladen Ground Spur, Aptian-Albian sandstone sequences (the Bosun Member)
are encountered in many wells, among others UK wells 16/27-1 and 16/27a-2
(100-130 m gross), 16/28-1 (50 m gross) and 16/28-6 (90 m gross).
The palaeogeographical position of these sandstones, i.e. basinal areas
close to the subaerially exposed major structural highs mentioned above,
may be quite similar to the palaeogeographical situation along the western
margin of the Måløy Fault Blocks. Here, up to 400 m (gross) thick sandstone sequences of Aptian-Early Cenomanian age were deposited in Norwegian blocks 35/3 and 36/1, and are defined as the Agat Formation in this paper.
The Devil's Hole Formation (UK well 29/25-1) and the "Unnamed Formation" (UK well 14/20-5) in the UK sector are comparable to the Ran sandstone units.
