Outcrop analogue studies can significantly improve the understanding of fracture distribution and their impact on fluid flow in hydrocarbon reservoirs. In particular, the outcrops may reveal details on the relationships between mechanical stratigraphy and fracture characteristics. This has been investigated in an integrated sedimentological-structural geological study in the Aquitanian sequence of the Asmari Formation on the NE limb of the Khaviz Anticline in the Zagros foothills in SW Iran. The Aquitanian sequence was deposited in a platform top setting and is characterized by well-defined bedding planes and relatively thin layers (<4 m) with rapid changes in textures from laminated peritidal mudstones to bioclast and ooid grainstones. Fractures in the studied area dominantly strike parallel to the fold axis, have a high angle to bedding and are stratabound. In the literature it is often reported that fracture spacing or the inverse fracture intensity (FI) is controlled by the mechanical layer thickness (MLT). However, in the present study area a rather poor correlation between FI and MLT was observed. Instead, the Dunham texture appears to be more important for the FI. Mud-supported textures (mudstone and wackestone) have higher FI than grain-supported (packstone and grainstone) ones. The degree of dolomitization does not appear to have any significant effect on FI within each texture class. A strong relationship between FI and MLT is observed generally in cases where there has been one single phase of extension and when interbed contacts are weak, e.g. interbedded competent limestones and incompetent shales. However, in the present study area a rather complex deformation history exists and well-developed shales between fractured carbonate layeres are lacking. It is suggested that in such cases the MLT is of minor importance for the FI, which is controlled by the texture.

The carbonate reservoirs in the Late Oligocene—Early Miocene Asmari Formation in the Dezful Embayment of SW Iran are characterized by low matrix permeability, and effective drainage is dependent on the occurrence of open fractures. Limited information on fracture orientation and fracture density is available from core and borehole image data, and high-quality/high-resolution three-dimensional seismic is often lacking in this area. Well and core data do not contain information on important fracture parameters like length distribution, crosscutting relationships, fracture density v. lithology and bed thickness. The understanding of fracture distribution and formation in the region and their effects on fluid flow has been greatly improved by the use of outcrop analogue data. Exposures of the Asmari Formation in the Khaviz Anticline are in close vicinity to the giant hydrocarbon fields. The Khaviz Anticline has a similar geometry and structural history to the major hydrocarbon fields in the area, and represents an excellent analogue for these. Two types of fracture features were observed: diffuse fracturing and fracture swarms. The diffuse fractures form networks and comprise structures grouped into four fractures sets, which are the typical for this type of anticline. Two orthogonal fracture sets are oriented parallel and perpendicular to the fold axis, and two conjugate fracture sets are oblique to the fold axis with their obtuse angle intersecting the trend of the fold axis. The fractures are typically stratabound, sub-perpendicular to bedding and commonly about the bounding stratigraphic surfaces. To a large extent the density and height of fractures in the Asmari Formation are controlled by the mechanical stratigraphy, which is controlled by the depositional environment and cycles. These outcrop data have been essential in the generation of discrete fracture network (DFN) models and the population of the fracture properties in the reservoir models.

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