The Rock Model - Reservoir Model Design - page 21

Fig. 2.6 The addition of hierarchy by logical combina-
tion: single-hierarchy channel model ( top left , blue ¼
mudstone, yellow ¼ main channel) built in parallel
with a probabilistic model of lithofacies types ( top

right , yellow ¼ better quality reservoir sands), logically
combined into the final rock model with lithofacies
detail in the main channel only - an additional level of
hierarchy

Some degree of hierarchy is implicit in any
software package. The modeller is required to
work out if the default hierarchy is sufficient to
capture the required concept. If not, the workflow
should be modified, most commonly by applying
logical operations.
An example of this is illustrated in Fig. 2.6 ,
from a reservoir model in which the first two
hierarchical levels were captured by the default
software workflow: tying layering to seismic
horizons (first level) then infilled by sub-seismic
stratigraphy (second level). An additional hierar-
chical level was required because an important
permeability

lithofacies types within a particular model element
(the main channels). The chosen solution was to
build the channel model using channel objects and
creating a separate, in this case probabilistic,
model which contained the information about the
distribution of the two lithofacies types. The two
rock models were then combined using a logical
property model operation, which imposed the tex-
ture of the fine-scale lithofacies, but only within
the relevant channels. Effectively this created a
third hierarchical level within the model.
One way or another hierarchy can be
represented, but only rarely by using the default
model workflow. heterogeneity existed between