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In terms of net-to-gross ratio (sand content
vs
.
shale content) within the Ness-Tarbert formations,
the western part shows lower ratios with low
sand-connectivity and thicker and more abundant
coal layers. In the eastern part of the well correla-
tion panel (Fig. 4), there is a higher net-to-gross
ratio with only a few thin coal layers. In the over-
lying Viking Group, the Heather Formation shows
a pronounced (37 times) westward thickness
increase (Table 2), whereas the Draupne Formation
portrays a more irregular thickness distribution.
The seismic cross-section (Fig. 4) is tied to for-
mation-picks in the wells. The quality of the seis-
mic resolution at this depth is not sufficient to
replicate the thickness trends within the Brent
Group directly, as seen in the wells. However, a
general westward-thickening trend of the com-
bined Triassic and Jurassic package is seen on the
seismic cross-section, with the wedge-shaped unit
of the Late Jurassic syn-rift strata being the most
obvious. Three major fault-blocks are seen in the
seismic cross-section, which progressively steps
down eastward, i.e. into the northern Viking
Graben. The western Rimfaks fault-block is the
shallowest and the Kvitebjørn fault-block to the east
is the deepest. The smaller normal faults are pre-
dominately limited to the Jurassic or older strata
and tend to terminate within the Upper Jurassic
syn-rift strata. Only a few of these are seen to offset
the Base Cretaceous.
Fig. 5 shows two well correlations across
Permo-Triassic faults (according to Færseth,
(A)
W
E
33/9-6
34/7-19
34/7-15 S
34/8-6
34/8-3 A
Top Brent Gp.
E. Bajocian To p
Base Brent Gp.
~ 40 km
(B)
W
E
35/8-1
35/8-3
35/8-5 S
Top Brent Gp.
E. Bajocian
E. Bajocian Top
Fig. 5.
(A) West-east well correlation
across the Visund (34/8), Snorre (34/7)
and the Statfjord Field (33/9), showing
westward thickening of the Brent Group
toward the Statfjord fault. (B) West-east
well correlation across the Vega Field
(35/8) showing increased Brent Group
thickness across a Jurassic fault (see
Fig. 1).
Base Brent Gp.
~ 15 km
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