Every reservoir is in some way unique. There are nevertheless generic issues pertinent to certain reservoir types and, in terms of model design, there are issues which inevitably require attention.
We don’t aim to cover all possible reservoir types but we do hope to indicate trains of thought which we have found fruitful in modelling studies. Along the way, we can elicit distinctions between models for clastic and carbonate reservoirs and some courses of action to take if the reservoir turns out to be fractured (which all reservoirs are).
If all reservoirs were just tanks of sand, this task would be trivial. In practice, geology and fluid dynamics combine in complex and intriguing but ultimately understandable ways. Adapting a line from Leo Tolstoy’s Anna Karenina:
Homogeneous reservoirs are all alike; every heterogeneous reservoir is heterogeneous in its own way.
We have chosen to group siliciclastic reservoirs by common depositional settings, namely: aeolian, fluvial, tidal-deltaic, shallow-marine and deep-marine. We then go on to consider carbonate and fractured reservoirs as ‘types’.
In practice, many carbonate reservoir systems contain siliciclastic units, and both sandstone and carbonate reservoirs may be significantly influenced by the presence of faults and joints. The main issue is to identify the key characteristics of the reservoir under consideration as a starting point for the reservoir model design which will be unique to that reservoir.