Geoscience Reference
In-Depth Information
Fig. 6.7
Contrasting dune architectures: (
a
) dry aeolian systems; (
b
) fluvial-aeolian system; (
c
) sabkha aeolian sytems
(Image courtesy C.Y. Hern
2000
)
The hierarchical packaging of dune systems
by bounding surfaces has been well described (e.g.
Hunter
1977
;Kocurek
1981
;Fryberger
1990b
)
and the potential impact of their arrangement on
reservoir sweep efficiency investigated (e.g. by
Ciftci et al.
2004
). In the Ciftci et al. study, aeolian
bounding surfaces were seen to act as barriers to
flow, based on observations of the Tensleep Sand-
stone in Wyoming, whereas in the Scottish outcrop
example shown in Fig.
6.5
the bounding surfaces
are clearly open to flow. Either scenario is possible.
Assuming the permeability of the bounding
surfaces can be determined, the central questions
for forecasting reservoir flow patterns (sweep
efficiency) are:
which reservoir element
significantly below that of the well spacing, the
permeability of the overall system is dominated
by the poorer quality unit (Fig.
6.8
). In this case it
can be argued that explicit modelling of the
'detail' is not necessary because irregularities in
the sweep pattern disperse over the inter-well
volume and the permeability of the reservoir
system will start to approximate a predictable
average.
However, if the slip-face sands connect, or
congregate preferentially in specific units, the
heterogeneity needs to be explicitly captured.
6.1.4 Aeolian System Anisotropy
is the connecting
medium, and
what is the scale of the element distribution
relative to the well spacing (for a given pro-
duction mechanism, e.g. water injection)?
If high permeability slip-face sands are
embedded in poorer quality sands on a scale
For aeolian systems the key is therefore to iden-
tify the dune types and internal stacking patterns.
A strong overprint on aeolian architecture is
commonly the effect of changing base levels
(the 'stokes surfaces' of Stokes
1968
) or climatic
