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relative sea-level changes thus cannot be ruled out
as a potential control on sequence boundary for-
mation and associated basinward shift in facies as
seen within the Åre 5.2 and 6.2 reservoir Sub-
zones. Furthermore, regional change in rift basin
geomorphology may have been responsible for
amplifying tidal resonance within the basin (e.g.
Carr
et al
., 2003; Yoshida
et al
., 2007) and causing
tidal current dominance in the younger Åre
Formation deposits (Åre 5 and 6 Zones). A signifi-
cant tectonic influence during deposition of the
succession is also confirmed by the change in
provenance from East Greenland during deposi-
tion of the fluvial Åre 1 and 2 Zones to an eastern
source for the tide-influenced Åre 5 and 6 Zones
(cf. Morton
et al
., 2009).
became challenging. Both daily operational activi-
ties and long term reservoir management deci-
sions were severely influenced by the lack of a
reliable stratigraphic model.
The cross-section in Fig. 26 shows an example
of the previous reservoir zonation plotted on top
of the current updated model. Several distinctions
between the two stratigraphic models are illus-
trated by the well correlations; 1) Some key sur-
faces were not recognised in the previous reservoir
zonation (e.g. the surface cSB2 (Fig. 18) is located
within the former Åre 2.8 Sub-zone); 2) Some
of the former sub-zones were defined on not-
recognisable geological criteria (e.g. inclusion of
sub-zones Åre 2.6, Åre 2.7 and partly Åre 2.8
within the current Åre 5.1 Sub-zone) and; 3) the
top of the former Åre 2.6 Sub-zone cuts across the
key FS-marker at top of the current Åre 4 Zone.
These distinctions are primarily caused by lack
of documented geological criteria of the strati-
graphic framework in the previous model. Several
other examples of such distinctions can be infer-
red from Fig. 4. Inconsistencies, such as those
described above, were a major concern and devel-
opment of a simpler stratigraphic model was a
main objective. Despite the underlying complex-
ity in the sedimentology of the Åre Formation,
the current update has enabled an intuitive and
predictive grouping of facies associations into
genetically related packages. The simplicity in
this model construction is also easy for non-
geologists to adapt.
INDUSTRIAL APPLICATIONS
The shift of focus from producing from high qual-
ity Fangst reservoirs to the low productivity Åre
Formation formed one of the main drivers for
undertaking a complete update of the Åre reser-
voir stratigraphy in the Heidrun Field. Lack of
robustness in existing stratigraphic models was
the other main driver. However, in a large and
mature field like Heidrun, the update of the strati-
graphic model represents a major investment that
affects all subsurface disciplines. In this section,
a few examples of industrial applications that
motivated this investment are presented.
General impact of a revised
stratigraphic model
Impact on reservoir models and calculation
of hydrocarbon volumes
Within the oil industry, the reservoir zonation is
one of the very few elements of reservoir charac-
terisation that is passed on throughout the entire
value chain from one discipline to another. It is
applied in seismic interpretation, reservoir mod-
elling, production forecast (reservoir simulation),
well planning, drilling operations, measures for
increased oil recovery and allocation of produced
volumes. All disciplines have a close relationship
to the field's reservoir zonation and a well-defined
stratigraphic model has a significant intrinsic
value in all interdisciplinary communication.
In the Heidrun Field's expanding well database,
the previous reservoir zonation had become unre-
liable (Fig. 4). Well-to-well correlations could not
be achieved in a consistent manner and maintain-
ing a geologically predictable reservoir zonation
Updates of in place hydrocarbon volumes and
extractable reserves are primarily dependent on
petrophysical evaluation models and the choices
made when implementing geological reservoir
models into numerical representations. Some of
the most important outcomes of the revised strati-
graphic framework in the Heidrun Field are
improved robustness in volume calculation. This
has, in turn, resulted in updates of both hydrocar-
bon resources and reserves.
Reservoir modelling strategies commonly repre-
sent a choice between modelling details in facies
distributions and inherent uncertainties in spatial
arrangement and more general representations of
average reservoir properties disconnected from
facies analysis (i.e. data-driven observations of
lateral and vertical trends in reservoir quality).
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