Network of Offshore Records of Geology and Stratigraphy

NORLEX

Hvithval Member [new]

Introduction

The Hvithval Member is a detached member of the Springar Formation found in the Vøring Basin that has been drilled in wells on the structurally high areas of the Gjallar Ridge e.g. 6704/12-1 and Nyk High e.g. 6707/10-1 . The member consists of sandstones with subordinate, interbedded mudstones and siltstones with rare stringers of limestones and dolomites of Late Cretaceous, late Campanian - Maastrichtian age.

The sandstones are considered to have deposited by mass flow processes into a deep marine palaeoenvironment from the north or north-west during a renewed period of basin margin uplift and rifting and within the period of the rift climax stage of Færseth and Lien (2002).

Name

English/ Norwegian and any previous names: In the reference well 6707/10-1, the operator BP Norway, originally included this unit as Upper Paleocene sandstone within the Tang Formation.

Derivatio nominis: The name Hvithval is the Norwegian name for the white whale or Beluga species Delphinapterus leucas. The species is a toothed whale species of moderately large size (reaching up to 4.5m long) that are found in small schools or flocks in cold Arctic seas such as the Polar Sea around Svalbard and the Barents Sea.

Lithology

The Hvithval Member consists of sandstones with subordinate, interbedded mudstones and siltstones with very rare limestones and dolomites.

The sandstones are white - yellow light grey, medium grey - medium dark grey to light brown grey, clear quartz grains, transparent to translucent, colourless, white to pink, very hard, loose, very fine to coarse, predominantly fine to medium, occasionally very coarse, angular to rounded, generally sub-angular to sub-rounded, poorly to moderately sorted, well cemented, siliceous cement with occasional calcite cement, argillaceous, silty, occasionally pyritic, glauconitic, chloritic, micaceous, trace of carbonaceous material, with no or poor visible porosity, occasionally grading to siltstone.

The subordinate mudstones are light - medium grey to brown grey, predominantly firm, occasionally soft to moderately hard, amorphous to blocky or sub-fissile, with disseminated and nodular pyrite, glauconitic, micaceous, silty, sandy, occasionally very sandy, and moderately calcareous with occasional dark laminae.

The siltstones (developed particularly in the lower part of the member), are light to medium grey, soft to firm, friable, argillaceous matrix, disseminated pyrite, arenaceous with very fine to fine sand, micaceous, glauconitic, non to moderately calcareous.

The infrequent limestone stringers are white- very light grey to medium dark grey- brown grey, firm, microcrystalline, silty, occasionally sandy with traces of glauconite and micro- mica.

The dolomite stringers are white to very light grey, firm to moderately hard and blocky.

Basal Stratotype

SEE SECTION 8 (below)

Sample depository

Palynological preparations (organic matter depository)

Type well 6305/5-1: 19 slides from core samples covering the interval 2782.45m - 2812m deposited at the NPD (RRI and OD preparations).

Reference well 6707/10-1: 4 slides from ditch cuttings covering the interval 2230m - 2410m deposited at the NPD (DONG preparations).

Core photographs

Type well 6704/12-1: core#1 and core#2 covering the interval 2554mMD RKB - 3005.4mMD RKB.

This represents the uppermost part of the member and includes the unconformable upper boundary with the overlying Rogaland Group. The boundary is not readily identifiable in spite of being an unconformity. The boundary is a sand/sand contact and in addition to the marked difference in age, the overlying basal Tang Formation is characterised by glauconitic sandstones seen at the top of core #1 between 2554m and 2555.1 m (uncorrected measured depth). The core shift is -2.3m.

Reference well 6707/10-1: no core was taken in this member.

6704/12-1, 2554-2559 m	6704/12-1, 2559-2564 m	6704/12-1, 2564-2569 m
6704/12-1, 2569-2574 m	6704/12-1, 2574-2575 m	6704/12-1, 2997-3002 m
6704/12-1, 3002-3005 m

Thickness

The thickness of the Hvithval Member in released wells ranges from 221m - 691.3m.

Isochore map HVITHVAL

Geographical distribution

[Map] Sandstones of the Hvithval Member are geographically restricted to the Vøring Basin. With the available, limited well coverage in this area, this is located on the structurally high areas of the Gjallar Ridge e.g. 6704/12-1 and Nyk High e.g. 6707/10-1. It is absent, presumably due to early Cenozoic erosion on the Vema Dome e.g. 6706/11-1 and Utgard High e.g. 6607/5-1. However, time equivalent, mudstone dominated successions of the Springar Formation, are developed in the 6607/5-2 (flank of the Utgard High), 6605/8-1 (Stetind prospect; western flank of the Fles North rotated fault block) and 6505/5-1 (Helland Hansen Dome) providing a southerly limit to the members extent.

Occurrences of formation tops in wells

Type well

Well name: 6704/12-1
WGS84 coordinates: N 67°07'25.00, E 04°42'44.70 (figure 2)
UTM coordinates: 7446374.14 N 574282.36 E
UTM zone: 31
Drilling operator name: Saga Petroleum ASA
Completion date: 24.07.1999
Status: P & A
Interval of type section (m) & thickness in type well (m): 3244m - 2552.7m (2555.1m MD core depth) and 691.3m thickness.

Reference well

Well name: 6707/10-1
WGS84 coordinates: N 67°04'07.85, E 07°00'36.51 (figure 2)
UTM coordinates: 7440629.70 N 413490.42 E
UTM zone: 32
Drilling operator name: BP Norway Ltd
Completion date: 23.07.1997
Status: P & A
Interval of reference section (m) & thickness in reference well (m): 2434m - 2213m and 221m thickness.

Upper and lower boundaries

Upper Boundary

In the type well 6704/12-1, the top of the Hvithval Member is poorly defined in core although it represents the unconformable K/C boundary with the overlying Upper Paleocene Tang sandstones (informal) at 2555.1mMD (2552.8m corrected core depth). The boundary, therefore, represents a contact between two sandstones units of significantly different age separated by a stratigraphic break in the order of 10 m.y. The thin sandstones of the Tang Formation are characterised by glauconitic and bioturbated sandstones that are interpreted as representing a relatively shallow marine transgressive lag deposit that unconformably overlies the deep marine sandstones of the Hvithval Member. This is represented on wireline logs by a minor downward decrease in gamma-ray values that is probably related to the down section decrease in glauconite content of the sandstones and an increase in sonic velocity.

Lower Boundary

The base of the Hvithval Member is marked by the down section change from sandstones with interbedded mudstones to argillaceous sediments of the Springar Formation. It is marked on logs by a downward increase in gamma-ray values and a minor decrease in average sonic velocity. In the type well 6704/12-1, there is downward positive separation between neutron and density logs reflecting the down section development of mudstones but this is slightly above the gamma and sonic changes.

Well log characteristics

[Figure] In the type well 6704/12-1, the log profile of the Hvithval Member is generally irregular or serrate and this reflects the heterolithic interbedded character of the member. The gamma-ray log shows a predominantly serrate profile but cone-shaped, funnel-shaped and, more rarely, blocky-type profiles are developed that reflect variations in the original depositional setting and suggest that the sand was deposited under a range of mass-flow processes. The overall character of the log shows that the member contains several cycles that are variously dominated by intervals of either sandstones or mudstones. The marked increase in gamma- ray logs in the upper part of the Hvithval Member at 2685m MD RKB in the type well 6704/12-1 coincides with a cycle boundary (and possible candidate maximum transgressive surface- mts) that separates two overall progradational trends and cleaning upward gamma- ray profiles that can be tied to a prominent seismic reflector.

Type seismic section

Biostratigraphy

[Figure] The dating of the Hvithval Member is complicated by reworking from older stratigraphic levels (a mixture ranging from Permo-Triassic to Maastrichtian ages) and probably intra- member recycling. The age is primarily based on dinoflagellate cysts.

In the basal part of the member in the Gjallar Ridge type well 6704/12-1, the LCO Odontochitina operculata, LO O. costata, O. 'wetzelii' Wilson 1974 suggests an age at least as old as early Maastrichtian (Zone 23) and the associated occurrence of the dinocyst marker Palaeohystrichophora infusorioides is typical of the late Campanian (Zone 24). The LAO Heterosphaeridium heteracanthum in the underlying mudstones of the Nise Formation confirms a late Campanian age. In the Nyk High reference well 6707/10-1 the base of the Hvithval Member is slightly younger being above the Odontochitina plexus.

The youngest extent of the member in the type well 6704/12-1 is early Maastrichtian and developed below the LO Alterbidinium acutulum. In the reference well 6707/10-1, the upper part of the member is within the acme of Impagidium 'septentrionalis' indicating a slightly younger intra-late Maastrictian age.

In general, the microfaunas are dominated by typical Cretaceous agglutinated foraminifera, notably LO Caudammina ovula; LO Rzehakina epigona, LO Kalamopsis gryzybowskii and the planktonic foraminferal species LO Heterohelix globulosa.

In the type well 6704/12-1 the upper boundary of the Hvithval Member is unconformable and coincides with base of glauconite rich sandstones of the Tang Formation in core at 2555.1mMD (2552.7m corrected core depth). A stratigraphic break in the order of 10 m.y. is indicated. The overlying interval yields the Middle Paleocene dinocyst markers LO Isabelidinium viborgense, LO Palaeocystodinium bulliforme and LCO Palaeoperidinium pyrophorum.

Age

Late Cretaceous, late Campanian - late Maastrichtian range but mainly early Maastrichtian age (Zones 24 -23).

Correlation

[Figure] The Hvithval Member passes laterally into mudstones of the Springar Formation. This member is part of the K100 sequence of Vergara et al. (1999) and K90 sequence of Færseth and Lien (2002) and Lien (2005) and K90 sequence of Fugelli and Olsen (2005a and 2005b).

Depositional environment

Limited data is published on the depositional setting of the Hvithval Member.

The sandstones were deposited within a large scale, deep-water, distal basin floor fan (Fugelli and Olsen, 2005b) as part of their play 1 concept. The sandstones were presumably deposited by mass flow processes with sediments originating from the north or north-westerly locations towards the Greenland mainland.

In their study of outcrop analogues, Fugelli and Olsen (2005a), considered the sand-rich fan complex of the Brushy Canyon Formation in the Delaware Basin, USA to be an analogous system.

In the background mudstones of the member, the presence of agglutinated microfaunas (DWAF) suggest a relatively deep, upper to middle bathyal water depths with oxygen poor bottom conditions.

Remarks

References

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.

Fugelli, E. and Olsen T. R. 2005b. Risk assessment and play fairway analysis in frontier basins: Part 2 - Examples from offshore mid- Norway. AAPG Bulletin, 89(7), 883-896.

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.

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.

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