Skolest Member [new]
Shetland Group,
Blålange Formation
Introduction
Sandstones and minor subordinate mudstones of the new Skolest Member are developed within
the Blålange Formation (new) in quadrants 6305 (northerly part
of the Ormen Lange Field)
and 6306 in the Slørebotn sub-basin on the eastern margin of the Møre Basin. These
frequently glauconitic sandstones are of middle/late Turonian age and are characterised by
relatively uniform and blocky log profiles. The Skolest Member is stratigraphically older
than the Lysing Member of the Halten-Dønna Terraces and
equivalent sandstones of the
overlying Tunge Member developed along the eastern Møre margin.
There is no core data or published information on the depositional setting of the Skolest
Member. Based on the biofacies, the Skolest Member was deposited in a fully marine,
offshore palaeoenvironment below storm wave base.
Name
English/ Norwegian and any previous names:
None. The operator Norske Shell included the reference well
6306/10-1
as part of the 'Lysing Formation'.
Derivatio nominis:
The Skolest Member is derived from the Norwegian for the fish species Corypheonides
rupestris or round-nosed grenadier. This relative of the cod is a benthopelagic to
bathypelagic fish usually found from 400 m to 1200 m water depth in the North
Atlantic and Norwegian Sea and locally in either the Norwegian fjords or on the banks off
the coast of Møre and Trøndelag.
Lithology
The Skolest Member consists of sandstones and minor, subordinate mudstones.
The sandstones are white - light grey, clear to translucent quartz, predominantly
fine
grained but maybe very fine to coarse grained, angular to sub-rounded, predominantly
moderately sorted, loose grains with traces of calcareous cement, firm to moderately hard,
with trace to abundant glauconite, rarely micaceous and rare pyrite.
The mudstones are medium dark grey - dark grey, sub-blocky, firm to moderately
hard, non-calcareous, traces of micro-micaceous and rare traces of micro-pyrite.
Basal stratotype
In the type well 6305/1-1 the base of the Skolest Member is taken at 4529mMD RKB and is
characterised by a transitional change from mudstones of the underlying
Blålange Formation
to a sequence of predominantly sandstones of the Skolest Member. On wireline logs it is
marked by an upward transitional profile but distinct decrease in gamma ray values and an
increase in sonic velocities. The lower boundary is more marked on resistivity logs where
the boundaries is represented by an abrupt upward increase in values and the unit is
characterised by a uniform resistivity log profile.
See below for a complete description of both the lower and upper
boundaries and well log characteristics of the Skolest Member.
Sample depository
Palynological preparations (organic matter depository)
Type well 6305/1-1:
No slides are available from this member at the NPD.
Reference well 6306/10-1:
No slides are available from this member at the NPD.
Core photographs
Type well 6305/1-1: no cores
taken in this member.
Reference well 6306/10-1:
no cores taken in this member.
Thickness
The Skolest Member is between 10 m - 25 m thickness based on the available limited well
data.
Interactive Norlex isochore map for the Skolest Member
Geographical distribution
Based on the available, but limited well data, sandstones of the Skolest Member are
developed in the northern area of the Ormen Lange Field in quadrant 6305 and in the
Slørebotn sub-basin, quadrant 6306, towards the eastern margin of the Møre Basin.
Occurrences of member tops in wells
Type well
Well name: 6305/1-1
WGS84 coordinates: N 63°46'59.72", E 05°16'19.57"
UTM coordinates: 7075028.48 N 611981.31 E
UTM zone: 31
Drilling operator name: Norsk Hydro Produksjon A/S
Completion date: 19.11.1998
Status: P & A
Interval of type section (m) & thickness in type well:
4529 m - 4504 m, 25 m thickness.
Reference well
Well name: 6306/10-1
WGS84 coordinates: N 63°09'26.32", E 06°19'41.45"
UTM coordinates: 7006099.05 N 365416.35 E
UTM zone: 32
Drilling operator name: A/S Norske Shell
Completion date: 17.12.1990
Status: P & A
Interval of reference section (m) & thickness in reference well:
1999 m - 1992 m, 7 m thickness.
Upper and lower boundaries
Lower boundary
In the type well 6305/1-1 the base of the Skolest Member is taken at 4529mMD RKB and is
characterised by a transitional change from mudstones of the underlying
Blålange Formation
to a sequence of predominantly sandstones of the Skolest Member. On wireline logs it is
marked by an upward transitional profile but distinct decrease in gamma ray and density
log values and an increase in sonic velocities. The lower boundary is more marked on
resistivity logs where the boundaries is represented by an abrupt upward increase in
values and the unit is characterised by a uniform resistivity log profile. In the
reference well 6306/10-1, the lower boundary at 1999mMD RKB has a similar transitional
decrease in gamma ray values but a more distinct increase in sonic velocities and increase
in resistivity values.
Upper boundary
In both the type well 6305/1-1 and reference well 6306/10-1, the top of the Skolest Member
is marked by a sharp change in gamma ray, resistivity and sonic logs reflecting the
change from sandstones to mudstones of the overlying and surrounding
Blålange Formation.
The upper boundary is defined by a marked decrease in gamma-ray values and increase in
sonic velocity. In the 6306/10-1 reference well the upper boundary is associated with a
pronounced downward negative separation between neutron porosity and density logs in
response to the rapid termination of sandstones.
Well log characteristics
In both the type and reference wells the Skolest Member is characterised by relatively
blocky gamma-ray and sonic log profile with a slightly funnel-shaped lower boundary.
Type seismic section
NH 9602- INLINE 2016 & X-LINE 6916
Biostratigraphy
In the type well 6305/1-1 the presence of the dinocyst Stephodinium coronatum
(4526m swc) suggests an age no younger than Turonian.
In the reference well 6306/10-1, the Skolest Member is developed below the Coniacian
Tunge
Member and within a 'latest' middle - late Turonian age interval. The
dinocyst
marker LO Microdinium setosum below the member defines a an intra-middle Turonian
level
and above the Skolest Member is an influx of planktonic foraminifera with LAO
Hedbergella
delrioensis and the dinocyst LO Stephodinium coronatum characteristic of the
late Turonian (Zone 27). The Skolest Member is therefore developed close to the middle/late
Turonian boundary.
Age
Late Cretaceous, middle - late Turonian (Zone 27).
Correlation
The sandstones of the Skolest Member pass laterally into mudstones of the
Blålange Formation.
The Skolest Member is stratigraphically older than the
Lysing Member of the Halten-Dønna
Terrace area and the Møre Basin equivalent Tunge Member and this
relationship can be
demonstrated in the reference well 6306/10-1. It is therefore part of the K70 sequence of
Vergara et al. (2001; see their figure 4 but not discussed in any detail), K50
sequence of
Færseth and Lien (2002) and Lien (2005) and K67 - K68 sequence of Fugelli and Olsen (2005a
figure 2).
Depositional environment
There is limited data available on the depositional setting of the Skolest Member in the
absence of cores. In the absence of any apparent stratigraphic breaks in the adjacent
sections it is likely to be at least below storm base level. Marine microplankton
diversity is high (30-40 species) and suggests an open marine, offshore environment. In
terms of benthic foraminiferal biofacies the associations are extremely impoverished.
Tubular deep water agglutinated foraminifera DWAF are common in the overlying
Blålange
Formation down to 4130mMD reflecting a deep marine environment and coinciding with a
level
associated with an up-section decrease in average sonic velocities. Below this level
4134m MD - 4560m MD TD within the development of the Skolest Member, recovery is poor and
largely dominated by pyritised microfossils that may suggest an oxygen depleted bottom
environment although this interpretation is unreliable.
Remarks
The sandstones of the Skolest Member may contain abundant glauconite, as in the type well
6305/1-1, and this may be a distinctive feature of this member. It is unsure whether the
glauconite grains are in situ or represent reworking from up-dip shelfal settings.
References
Færseth, R. and Lien, T. 2002. Cretaceous evolution in the Norwegian Sea - a period
characterized by tectonic quiescence.
Marine and Petroleum Geology 19:1005-1027.
Fugelli, E. and Olsen T. R. 2005a. Screening for deep-marine reservoirs in frontier basins:
Part 1 - Examples from offshore mid- Norway.
AAPG Bulletin 89(7):853-882.
Lien, T. 2005. From rifting to drifting: effects on the development of deep-water hydrocarbon
reservoirs in a passive margin setting, Norwegian Sea.
Norwegian Journal of Geology 85:319-332.
Vergara, L., Wreglesworth, I., Trayfoot, M., Richardsen, G. 2001. The distribution of Cretaceous
and Paleocene deep-water reservoirs in the Norwegian Sea basins.
Petroleum Geoscience 7:395-408.
