Hydraulic flow units, depositional facies and pore type of Kangan and Dalan Formations, South Pars Gas Field, Iran

• There are six flow units in South Pars Gas Field.
• Hierarchical clustering is powerful technique for clustering flow units in heterogeneous carbonate reservoirs.
• High quality flow units mainly consist of shoal facies.

It is highly essential to characterize the reservoir as rigorously as possible to implement enhanced oil recovery operations and field development scenarios. In this scope, use of novel concepts and techniques for classification of reservoir rocks and definition of producing and non-producing zones will be greatly helpful. In the current research, hierarchical clustering is employed to characterize hydraulic flow units of four wells of South Pars Gas Field using core data. Studying the clustering tree, also known as dendrogram, it is proved that six is the optimal number of flow units for reservoir zonation. Cross plot of porosity versus permeability for each flow unit shows high cross correlation value, which confirmed the accuracy of employed technique for grouping the FZI data. The available core data were studied to identify the possible microfacies. Ten micofacies are distinguished including massive to laminated anhydrite, evaporite bearing fenestral dolomudstone, pellet grainstone, pellet wackestone to packstone, bioclastic wackestone to packstone/mudstone, bioclastic wackestone to mudstone, bioclastic ooid grainstone, ooid grainstone, intraclastic grainstone, and thrombolite boundstone. The frequency of each facies for each hydraulic flow units was investigated. The results indicate that presence of anhydrate severely reduced reservoir quality. According to thin section and core slab analyses results, high quality flow units mainly consist of bioclastic ooid grainstone, ooid grainstone, and intraclastic grainstone and thrombolite boundstone, which are associated with shoal facies. Finally, thin section and scanning electron microscope (SEM) analysis was done to recognize pore types of each flow unit.