Swarms cut obliquely across large parts of reservoir units from which most of the oil is produced.

In wells, they appear at relatively short depth intervals and are probably controlled by clustered fractures, although they could also result from a single open fault or a single fracture with an exceptionally wide aperture.

Carbonate successions in the Zagros mountains, with a close-up of superimposed fracture sets.

The diffuse term refers to minor fractures confined largely to specific beds – in other words, strata-bound – and occurring at high angles to the bedding.

Two-dimensional lateral variations in fracture intensity were modelled from fracture density maps based on a structural model of the field and borehole-derived productivity indexes.

To realise full-field discrete fracture network (DFN) models, the fracture density maps were combined with a three-dimensional model of fracture facies – in other words, distinctive recurring fracture systems – on the basis of production logs and mud-loss data.

The DFN models were then scaled up to representative fracture parameters used to simulate combined fluid flow – in other words, the interdependent, simultaneous flow of hydrocarbons through the matrix of the rocks and their superimposed fractures (known as dual-porosity dynamic simulation).

 Analogue outcrops were also studied to provide greater insight into fracture types, patterns and distributions.