Depositional facies and diagenetic control on reservoir quality of the Aptian Dariyan Formation, NW Persian Gulf

The Aptian Dariyan (Shu'aiba) Formation is one of the major Cretaceous reservoirs in the Middle East. Despite its economic significance, an understanding of the influence of depositional facies and a sequence of diagenetic events on its reservoir quality remains limited. Here, we address this challenge through analysis (facies, petrophysics, geochemistry) of a continuous, ∼180 m thick core from NW Persian Gulf, and a fully-automated identification of hydraulic flow units (HFUs). Ten carbonate and four predominantly siliciclastic facies were identified as part of four facies associations, from shallowest to deepest: mixed tidal flats, inner ramp (lagoon and shoals), shallow open-marine mid ramp, and deep open-marine (outer ramp and intrashelf basin). The stacking pattern of facies yields five third-order transgressive-regressive sequences. Three hydraulic flow units (HFUs) were identified and evaluated against lithology and petrophysical values: baffle unit (HFU1), normal unit (HFU2), and permeable unit (HFU3). The permeable unit exhibits good storage capacity and moderate flow capacity. The data reveal an overall complex paragenetic and porosity-modification history of the Dariyan Formation. The overwhelmingly mud-dominated texture of the facies, along with meteoric-zone dissolution under a predominantly warm and humid greenhouse climate during periods of relatively low sea level, and subsequent fracturing during deep burial played a major role in controlling the reservoir quality.