home
previous page		 NORLEX

Heimdal Member

Rogaland Group, Lista Formation

Unit definition

The Heimdal Member is attributed to the intra Lista Formation sandstones in subarea NW in Figs. 12, 13 and 72.

Name

The name Heimdal Formation was introduced by Deegan & Scull (1977) for sandstones age-equivalent to the mudstones of the Lista Formation. Knox & Holloway (1992) redefined the sandstones of the Heimdal Formation as Heimdal Member. This redefinition is maintained in this study.

Derivatio nominis

The Heimdal Formation (now Heimdal Member) is named after the Norse god Heimdal, one of Odin's sons.

Type well

Norwegian well 25/4-1 (Fig. 80): Depth 2067-2423m RKB. Coordinates N 59°34'27.30", E 02°13'22.60". Defined by Hardt et al. (1989).

Fig. 80. Well 25/4-1 Composite log Rogaland Group. Stratigraphic position of the Heimdal Member is outlined in stratigraphic column to the right.

Reference wells

Norwegian well 15/9-11 (New, Fig. 81). Depth 2385-2423 m RKB. Coordinates N 58°24'02.53", E 01°53'41.79". Core 3-4.

Norwegian well 15/9-5 (Fig. 82). Depth 2448-2716 m RKB (revised). Coordinates N 58°24'12.47", E 01°42'29.20". No cores. Defined by Hardt et al. (1989).

Fig. 81. Well 15/9-11 Composite log Rogaland Group. Stratigraphic position of the Heimdal Member is outlined in stratigraphic column to the right.

Fig. 82. Well 15/9-5 Composite log Rogaland Group. Stratigraphic position of the Heimdal Member is outlined in stratigraphic column to the right.

Composition

According to Knox & Holloway (1992), the Heimdal Member consists of thick sandstone units alternating with thinly bedded sandstones and mudstones. A core photo example is shown in Fig. 83 and a core description example in Fig. 84. The sandstones are friable to lightly cemented, moderately sorted and of very fine to coarse sand grade. They include minor and variable amounts of glauconite and are occasionally associated with thin beds of chalk. The interbedded mudstones are light to medium grey grading to olivegrey and greengrey. They are poorly bedded, and variably silty and generally non-calcareous.

Sandstone intrusions are frequently found associated with the upper boundary of sandstones bodies, often with an abundance of angular and tabular mudstone clasts.

Fig. 83. Core photograph of massive, faintly dish structured sandstones of the Heimdal Member. Well drilled by Norsk Hydro. Photograph from NPD Fact Pages at http://www.npd.no.

Fig. 84. Core description log from upper parts of the Heimdal Member well 25/8-6.

Wireline log characterization

Lower boundary

The Heimdal Member overlies the Lista and sometimes the Våle Formation, and the boundary is characterised by lower gamma readings and increased velocity upwards from the Lista or Våle Formation below.

Upper boundary

The Lista Formation usually overlies the Heimdal Member, and the boundary is characterised by higher gamma-ray readings and lower velocity upwards into the Lista Formation. Where the Hermod Member directly overlies the Heimdal Member, the boundary may be more difficult to define.

Thickness

The Heimdal Member occurs over much of the Viking Graben, and can attain thickness of more than 400 m in this area (436 m in well 24/6-2).

Seismic characterization

The seismic pick of the Top Heimdal Member is variable and varies from well defined positive acoustic impedance to poorly defined or even negative acoustic impedance. The Heimdal Member is often characterized by a mounded internal character within an envelope of mapped flooding surfaces or sequence boundaries. Fig. 85 shows a seismic cross section through two major bodies of the Heimdal Member, representing sand rich submarine fan deposits. Fig. 86 shows a seismic amplitude map of the uppermost Heimdal sand body in block 15/5, displaying a fan shaped high amplitude feature. This feature represents the sand rich submarine fan system that is reservoir rock in the Glitne Field.

Fig. 85. Seismic WE Line through southern parts of Block 25/10. The line shows partly mounded thicks. The two uppermost represent sub-members of the Heimdal Member.

Fig. 86. Seismic amplitude map from an internal event in the Upper part of the Lista Fm in Block 15/5. Fan shaped anomaly forms the reservoir in the Glitne Discovery, and is attributed to presence of the Heimdal L3 sub-member.

Age

Late Middle to Late Paleocene (Late Selandian to Early Ypresian).

Biostratigraphy and age

The Heimdal Member contains the acme occurrences of A. gippingensis and P. pyrophorum. The member is contained within the Lista Formation, thus corresponding in age to that of the Lista Formation, meaning late Selandian and Thanetian.

Correlation and subdivision

The acme occurrences of A. gippingensis and P. pyrophorum allow further subdivision of the Heimdal Member, related to the three-division of Lista, with distinction of Heimdal L1 Sub-members, Heimdal L2 Sub-members and Heimdal L3 Sub-member sandstones.

Geographic distribution

The Heimdal Member is more or less time equivalent to the Mey Member of the Outer Moray Firth and Central Graben. Limited interfingering of the two sand fan systems appears to have taken place over the Fladen Ground Spur (Figs. 12 & 13), and they are here separated along a line of supposed minimum sandstone thickness between the depocentres of the South Viking Graben and the Fisher Bank Basin (Knox & Holloway, 1992). The geographical distribution is mainly in the Viking Graben to Shetland Platform, with thin sands reaching the Viking Graben across the Tampen Spur (Fig. 72).

Occurrences of member tops in wells

Depositional environment

The sand rich Heimdal Member was deposited into coalescing sand fan systems. The sands were mainly transported with high density turbidity flow, depositing thick bodies of amalgamated sand beds, with minor heterolithic sandstone units being deposited in inter channel and terminal edge of depositional lobes. Water depths seem to have reached several hundreds of meters in central parts of the basin.

Hydrocarbon discoveries with Heimdal Member reservoirs



home previous page