Controls of depositional facies and diagenetic processes on reservoir quality of the Arab Formation in the one oil field, Southern Persian Gulf

The Late Jurassic Arab Formation is one of the main oil reservoirs in the Middle East. To investigate factors reservoir quality controlling, the integration of the results from geological and petrophysical data was utilized. Ten main facies were recognized and grouped in five facies belts of tidal flat, intertidal, lagoon, shoal, and shallow open marine, indicating deposition of the formation on a homoclinal carbonate ramp platform. The diagenetic processes occurred in marine, meteoric, and burial diagenetic realms. According to the frequency within the reservoir, five main pore types comprising intercrystalline, interparticle, vuggy, moldic, and microporosity were determined. Four third-order depositional sequences which are correlatable with four reservoir zones (A–D) of the Arab Formation were identified. The development of grainstone facies played an important role in high reservoir potential intervals. In view of their controls on reservoir quality, diagenetic features can be categorized into two classes: (1) diagenetic processes enhancing reservoir quality that include dissolution, dolomitization, and fracturing; (2) diagenetic processes reducing reservoir quality including cementation, evaporate mineralization, overdolomitization, and compaction. Considering its layer cake nature, it is possible to use petrophysical logs for the correlation of different reservoir zones, and depositional sequences between the studied wells.