Controls of depositional facies and diagenetic processes on hydraulic flow units of the Shurijeh Formation in the one Gas field, Northeast of Iran

Shurijeh Formation (Neocomian - Barremian) is the main hydrocarbon reservoir in north east Iran. Most gas reservoir production place in zones B and D of this formation. In this study, comprehensive petrographic and petrophysical studies were performed to understand the factors controlling the reservoir quality of this formation. With respect to the petrographic studies, well log data, evidence achieved from the core and drill cuttings, five primary facies (petrofacies), including microconglomerate, sandstone, claystone/shale, sandy dolomudstone, and dolomitic- sandy dolomitic ooid grainstone / hybrid, were identified in the deposits of Shurijeh Formation. Sedimentary facies of the Early Cretaceous reservoir in the studied wells belong to the upper part of the supratidal zone, intertidal zone, lagoon, braided river (longitudinal bars) and meandering river (flood plain and oxbow lake). In this study, based on porosity and permeability data, 4 units of Hydraulic flow units (HFUs) were identified using flow zone indicator (FZI) method. The results of this study showed that the diagenetic processes like dissolution, dolomitization and chemical compaction (stylolites and dissolved vein) are related to the grain supported facies including micro-conglomerate, sandstone and dolomitic- sandy dolomitic ooid grainstone / hybrid and hydraulic flow units (HFU4) and hydraulic flow unit (HFU3) that have the best reservoir quality are connected. The results of this study showed that the diagenetic processes like dissolution, dolomitization and pressure dissolution (stylolites and dissolved vein) are related to the grain supported facies including micro-conglomerate, sandstone and dolomitic- sandy dolomitic ooid grainstone / hybrid and hydraulic flow units 4 and 3 that have the best reservoir quality are connected. Diagenetic processes of cementation (Silica, carbonate and anhydrite) and alteration of feldspars are associated with the dominant mud facies including claystone/shale, sandy dolomudstone of hydraulic flow units 2 and 1 which have the lowest reservoir quality.