Tectonic control on sedimentation, erosion and redeposition of Upper Jurassic sandstones, Central Graben, North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 498

and sediment failures. However, both tectonically-
influenced effects and tropical storms could have
contributed to generating shallow water turbidity
current in the Central Graben. Similar interactions
are inferred for other wave-dominated shelves
(Pattison et al ., 2007).
With the benefit of more wells, it has been
demonstrated that the base Franklin C Sandstone
erosive unconformity cuts down around 90 m into
the underlying Franklin B Sandstone succession
in the northern part of the Elgin Field (Fig. 17).
The location of this erosion reflects the dynamic
interaction of salt movement, sediment loading
and, most significantly, grounding of the Elgin
pod on the underlying Rotliegend (Fig. 15). The
Franklin C Sandstone, which lies above the
unconformity surface, shows different thickness
trends to the Franklin B Sandstone below the
unconformity due to a change from pod filling to
pod collapse. Thickness trends in the Franklin C
Sandstone are the same as those in the overlying
Heather Shale Formation and markedly different
to changes in parasequence thickness recognised
through correlation of the Franklin B Sandstone
(shown in Fig. 17). Hence, deposition was con-

trolled by the interaction between tectonism and
the change from shoreface to turbidite deposition
(Fig. 19).
Updated correlation and mapping of the major
intra-reservoir erosion surface described above
allows a more rigorous correlation of the parase-
quences in the sandstones above and below the
erosion surface and the improved mapping of res-
ervoir quality based on well log and core-based
facies and petrophysics. Most importantly, the
new stratigraphic scheme better captures proximal-
distal facies trends, which are the main control
on reservoir quality. Together with changes to the
structural model, these are the two most significant
factors which probably influence field volumetric
calculations.

Case Study 4: The Fulmar Field:
Type B - Reactivated pod setting

Within the Fulmar Field, the Ribble Sandstone
Member represents the last phase of Fulmar
Sandstone deposition (Johnson et al ., 1986;
Robinson, 1990; Stockbridge & Gray, 1991; Clelland
et al ., 1993; Kuhn et al ., 2003; Figs 3 and 20). The

30/16-A35 30/16-A25 30/16-A23 30/16-A27 S1 30/16-A10 S1 30/16-A08 S2

Cretaceous

100 m

Fulmar Field

30/16-A8 S2

30/16-A10 S1

30/16-A27 S1

30/16-A23
30/16-A25
30/16-A35

Auk
Horst

1km

M.-U. shoreface sst

Offshore shale

Lw. Shoreface sst Turbidite sst

631000 632000 633000 634000 635000 636000

Fig. 20. Fulmar Field correlation showing truncation of the Fulmar Formation shoreface sandstones and reworking as
Ribble Member turbidite sandstone (after Kuhn et al ., 2003). Gamma ray logs indicate changes in clay content.