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upward or/and towards the W and SW into weakly
bioturbated, fine-grained to medium-grained het-
erolithic tidal point-bar deposits (2 m to 3 m thick)
of FA9 (Fig. 21C).
Overall, the mid-Tilje interval (T3.2) shows
more-or-less constant thickness across the study
area, with a slight lateral increase (up to 25 m)
towards the southern and north-eastern parts of
the Smørbukk field (Fig.  19, cross sections I and
II). The facies distribution within reservoir zone
T3.2 (Fig. 21C) shows only slight variability across
the field. The percentage of coarse and medium
cross-bedded sandstone is, however, higher in
the  north and central areas, in comparison with
the SE, where medium-grained to fine-grained
sandstone-dominated heterolithics are more
abundant. These subtle thickness and grain size
variations suggest a NE to SW proximal-to-distal
trend within the channel deposits.
The T3.2 succession is overlain by the stacked
tidal-fluvial channels (FA8), point-bar (FA9),
interdistributary bay (FA10) and distributary
mouth-bar deposits (FA3) of reservoir zone T4
(~25 m thick). In well logs (Fig. 3), the base of T4
is difficult to recognise; however, there is a subtle
inflection on the GR logs (from lower to higher
readings) and a lithologic separation (from finer to
coarser) in the DEN-NEU log, which is more
marked towards the east and less pronounced in
the central and northern areas. In GR-log curves,
the upper part of T4 consists of relatively clean,
coarsening-up or blocky sandstone. The top of the
unit (T4-T5.1 contact) is marked at the inflection
point (high to low GR reading) and is easy to iden-
tify in the north but is less prominent towards the
SW part of the field.
The erosively based tidal-fluvial channel deposits
(FA8) of T4 show similar characteristics to those in
zone T3.2. However, vertical burrowing (large-scale
Diplocraterion ) is more abundant and conglomer-
atic basal lags are rare and mainly localised in the
NE and central areas (Fig.  21D). Locally, the tidal-
fluvial channels change towards the SW into fine-
grained point-bar deposits (FA9) and to the east into
0.5 m to 1 m thick mud and mixed heterolithic
interdistributary bay (FA10) deposits (Fig.  21D),
showing rooted beds and organic-matter lenses and
small-scale wave-generated structures. Distributary
mouth-bar deposits (FA3) are also present and they
commonly occur towards the south of the field
(Fig. 21D).
As in the underlying reservoir zone, the T4
channel deposits are overall thicker and more
common in the northern and central parts of the
field, with interdistributary-bay deposits occur-
ring toward the east. Coarse-grained to medium-
grained channel-fill deposits are replaced towards
the south by medium-grained to fine-grained
distributary-mouth bars suggesting an NE to SW
proximal to distal trend. Grain-size and facies
variations are also accompanied by lateral changes
in the trace-fossil assemblage, from high-energy,
low-diversity (large Diplocraterion burrows)
within channel fills to more brackish-water assem-
blages showing low to small-scale Skolithos and
capping plant roots in the interdistributary bay
deposits and to a moderately diverse mixed
Cruziana and Skolithos suite in the southern
distributary-mouth bars.
Upper Tilje (T5 to T6)
The T4 tidal-fluvial channel deposits (FA8) are
regionally overlain by heterolithic distributary
mouth bar (FA3), tidal-fluvial channel fill (FA8)
and wave-influenced (FA6) and storm-influenced
(FA7) delta-front deposits in reservoir zone T5
(25 m to 30 m thick). The contact between T4 and
T5 is interpreted here as a high-order flooding sur-
face based on the increase of trace-fossil diversity
at the base of T5 and the upward switch to more
wave-influenced and storm-influenced delta-front
deposits, indicating a more distal depositional
setting compared with the proximal channel-fill
deposits of T4. This contact is well defined (in the
north and central areas) in GR/RES-log curves as
an inflection point from low to high values (Fig. 3),
coupled with the change in lithologic separation
on the Density-Neutron logs. However, the inflec-
tion point in the GR/RES curve and lithological
separation are less prominent towards the south
of the field.
The thicknesses of T5 increases slightly towards
the SW and NE of the field (Fig. 19, cross sections
I and II), where clinoforms dipping (2 degrees to 5
degrees) towards these directions have been inter-
preted from core and well-log data. This reservoir
unit is divided in two sub-zones (T5.1: 20 m thick;
T5.2: 5 m to 10 m thick) based on the upward
change of facies and the change from low to high
GR-log readings (Fig. 3).
The base of T5.1 consists of channelised distribu-
tary-mouth bar (FA3) and tidal-fluvial channel (FA8)
deposits. The mouth bars (FA3) show coarsening-
upward and sanding-upward successions composed
mostly of sand and mixed sandstone-mudstone,
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