Facies Characteristic, Diagenesis, and Reservoir Characterization of Lower Cretaceous Fahliyan Formation in a Heavy Oil Reservoir in the Persian Gulf

The Lower Cretaceous Fahliyan Formation, part of the Khami Group, overlies the Hith Formation and is overlain by the Gadvan Formation.

Petrographic studies led to the recognition of sixteen microfacies that were deposited in six facies belts (tidal flat, lagoon, reef, shoal, channel, and shallow open-marine).

Assessment of porosity and permeability according to microfacies, SEM, and convential core analysis indicates that microfacies of shoal and channel facies belts (Fh-MF8, Fh-MF9, Fh-MF10, and Fh-MF11) and one microfacies of lagoon with grain-supported texture (Fh-MF6) have good reservoir quality due to abundance of interparticle porosity. Microfacies of tidal flat facies belt has also good reservoir quality due to fanestral porosity. Microporosity is dominant in most facies of the studied samples. The samples with this pore type (such as most microfacies of shallow open marine and lagoon facies belts) do not have enough permeability to make a good reservoir zone.

Lower Fahliyan mainly consists of highly oil stained porous limestone and has better reservoir quality in comparison with upper parts due to abudance of interparticle and fenestral porosities.