Lithofacies analysis, sedimentary environment and sequence stratigraphy of the Burgan Formation in the North West of Persian Gulf, Iran

The Cretaceous Burgan Formation is one of the most important hydrocarbon producers in Persian Gulf, offshore Iran. To understand the lithofacies, depositional setting and depositional sequnces of the reservoir from Foroozan oil field in this area, detailed sedimentological study has been carried out on about 62.5 m of conventional core. The Burgan Formation in the studied oil field mainly consists of very fine to medium-grained sandstone, claystone, carbonaceous shale and some limited carbonate intervals.The combined results of both macro and microscopic investigations indicate eight different depositional facies in the studied interval of Burgan reservoir. These facies are consecutively numbered from 1 to 8. These are: (1) Cross-bedded channel sandstones, (2) Silty/sandy claystone; mud flat/bay facies, (3) Fine-grained sandstone with interlayers of shale; sand flat facies, (4) Alternation of fine-grained sandstone/siltstone and organic-rich shale; sand flat/mud flat alternation, (5) Silty claystone with plant remains; marine-influenced mud flat/shore face facies, (6) Fine-grained glauconitic sandstone along with sandy dolostone layers; marine influenced sand flat/shore face facies, (7) Organic-rich dark shale; restricted bay/marsh facies and (8) Ooid grainstone; oolitic shoal facies. Based on sedimentary features such as rhythmic alternation of sandstone-shale couplets, thick-thin alternations of silt and clay layers, flaser bedding, lenticular bedding, marine trace fossils and deepening up-ward successions in the cored interval, it seems that the Burgan Formation has been deposited on a tide-dominated estuary system. The studied interval of the Burgan Formation consists of several fining up-ward successions. These successions comprise four depositional sequences. Each sequence is started with lowstand channel sandstones and terminated with highstand shales and claystones.