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Odin Member

Rogaland Group, Balder Formation

Unit definition

The Odin Member is attributed to the Intra Balder Formation sandstones in Subarea NW in Figs. 12 and 13.

Name

The name Odin Member was proposed for sandstones in the Balder Formation by Mudge & Copestake 1992. The Odin member is age and lateral equivalent to the shallow to slope marine sandstones of the Dornoch Member further to the west.

Derivatio nominis

The Member is named after the Norse God Odin.

Type well

UK well 9/18a-15. Depth 1676-1875 mRKB. Coordinates N 59°26'36.670", E 01°33'20.080" (coordinates of 9/18a-4).

Reference wells

Norwegian well 25/7-17 (Fig. 133) . Depth 1587-1647 mRKB. Coordinates N 59°03'26.66", E 02°29'06.59". Cores: Core 1 and 2.

Norwegian Well 30/7-2 (Fig. 134) . Depth 1955-2004 mRKB. Coordinates N 60°29'26.06", E 02°01'40.85". Cores: Cores 7 and 8.

Fig. 133. Well 25/11-17 Composite log Rogaland Group. Stratigraphic position of the Odin Member is outlined in stratigraphic column to the right.

Fig. 134. Well 30/7-2 Composite log Rogaland Group. Stratigraphic position of the Odin Member is outlined in stratigraphic column to the right.

Composition

The sandstones are well to moderately sorted, clean and poorly cemented, although tightly cemented sandstones occur locally. Grains are medium rounded to sub angular. A core example from the Odin Member is shown in Fig. 135. Sandstone intrusions are frequently found associated with the upper boundary of sandstones bodies, often with an abundance of angular and tabular mudstone clasts.

Fig. 135. Core photo from lower parts of the Odin Member in well 25/11-17. Sediments are interpreted as high density turbidites influenced by secondary water escape and sand mobilization. Note striped appearance of bedded shale. Darker lamina represent normal anoxic shales, whereas lighter lamina/thin beds represent tuffs. Well drilled by Norsk Hydro. Photo from NPD Fact Pages at http://www.npd.no.

Wireline log characterization

The sandstones of the Odin Member often have a blocky appearance, but also serrated log pattern or fining/coarsening upwards patterns can be seen in some wells. Sometimes the Odin Member can be difficult to distinguish from gamma-ray and sonic logs, since the surrounding tuffaceous Balder Formation has relatively low gamma-ray readings and high velocity. In such cases resistivity and porosity/density logs can be useful.

Lower boundary (revised)

The basal contact of the Odin Member is seen as the boundary between shales of the Sele or Balder Formation and the lower parts of the Odin Member. The boundary is placed where there is an upwards transition from higher gamma-ray readings and higher velocity in the shales to lower gamma-ray readings and higher velocity in the sandstones.

Upper boundary (revised)

The Odin Member is overlain by the Balder Formation with variable amounts of tuff. The transition from the Balder Formation is usually seen as a downwards decrease from low/intermediate gamma-ray readings to lower gamma-ray readings together with an increase in velocity readings.

Thickness

Sandstone units up to 200 m thick, belonging to the Odin Member, occur in central and northern parts of the Viking Graben (Knox & Holloway, 1992).

Seismic characterization

The seismic character of the Odin Member varies from mounded to lenticular or trough shaped channel infills. Sometimes the top of the sandstones of the Odin Member is associated with a marked change in acoustic impedance and an increased amplitude (Fig. 130 rightmost parts) . In other cases the top of the Odin Member is difficult to recognize, and its presence is inferred from a thickening of the Balder Formation interval (central left in Fig. 136) .

Fig. 136. WE seismic cross section through area between Northern Balder and Grane discoveries, Blocks 25/10 and 25/11. Inferred presence of the Odin Member is highlighted.

Age

Earliest Eocene (Early Ypresian).

Biostratigraphy

Being contained in the Balder Formation, the age of the Odin Member is bounded by biostratigraphy and age assignments for the Balder Formation. See description for the Balder Formation in Subchapter 7.1.

Correlation and subdivision

The Balder Formation, which contains the Odin Member, is divided into a lower very tuffaceous unit (B1) and an upper less tuffaceous unit (B2). Sandstones of the Odin Member mostly belong to the B1 unit of the Balder formation (Odin B1 sandstones), but sandstones are also found in the B2 unit (Odin B2 sandstones).

Geographic distribution

In the Norwegian sector, the Odin Member is mostly restricted to the Viking Graben, but it is also found locally at the Utsira High, as for example in the Balder Field (Figs. 12, 13 and 132) , and in well 25/11-17, east on the Utsira high.

Occurrences of member tops in wells

Depositional environment

The Odin sandstones are mostly interpreted as representing mass flow transport and deposition in channels or fans sourced from shallow marine environments of the East Shetland Platform. Some sandstones are considered to have been emplaced by injection from lower levels.

Discoveries with the Odin Member as reservoir



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