Geoscience Reference
In-Depth Information
Fig. 4.18
Examples of geologically-based reservoir sim-
ulation models at four scales
(
a
) Model of pore space used as the basis for multi-phase
pore network models (50
(dimensions 80 m
3 km);
(
d
) Reservoir simulation grid for part of the Heidrun field
illustrating grid cells displaced by faults in true structural
position (dimensions 200 m
1km
m cube);
(
b
) Model of lamina-sets within a tidal bedding facies
(dimensions 0.05 m
μ
3km
5 km)
(Statoil image archives,
Statoil ASA, reproduced with
#
0.3 m);
(
c
) Facies architecture model from a sector of the Heidrun
field showing patterns of
0.3 m
permission)
tidal channel and bars
are based both on the nature of rock heterogeneity
and the principles which govern macroscopic flow
properties. In this discussion, we assume four
scales - pore, lithofacies, geomodel and reservoir.
This gives us three scale transitions:
1.
Pore to lithofacies.
Where a set of pore-scale
models is applied to models of lithofacies
architecture to infer representative or typical
flow behaviour for that architectural element.
The lithofacies is a basic concept in the
description of sedimentary rocks and
presumes an entity that can be recognised
routinely. The lamina is the smallest sedimen-
tary unit, at which fairly constant grain depo-
sition processes can be associated with a
macroscopic porous medium. The lithofacies
comprises some recognisable association of
laminae and lamina sets. In certain cases,
where variation between laminae is small,
pore-scale models could be applied directly
to the lamina-set or bed-set scales.
2.
Lithofacies to geomodel.
Where a larger-scale
geological concept (e.g. a sequence strati-
graphic model, a structural model or a diage-
netic model) postulates the spatial arrangement
of lithofacies elements. Here, the geomodel is
taken to mean a geologically-based model of
the reservoir, typically resolved at the sequence
or zone scale.
3.
Geomodel to reservoir simulator.
This stage
may often only be required due to computational
limitations, but may also be important to ensure
good transformation of a geological model into
3-dimensional grid optimised for flow simula-
tion (e.g. within the constraints of finite-
difference multiphase flow simulation). This
third step is routinely taken by practitioners,
whereas steps 1 and 2 tend to be neglected.
Features related to structural deformation
(faults, fractures and folds) occur at a wide
range of scales (Walsh et al.
1991
; Yielding
et al.
1992
) and do not naturally fall
into a
