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Regional Stratigraphic Architectures and Depositional Settings of the Giant Shu'aiba Reservoir in the Arabian Basin, and Their Implication in Reservoir Characterization and Exploration


The Early Cretaceous Aptian Shu'aiba reservoir is one of the most prolific giant carbonate reservoirs in the Middle East and is well-known for its complex architectures and heterogeneous reservoir characteristics. This complexity is due to the development of rudist buildups, clinoforming geometry, syn-depositional tectonics and complex diagenetic overprint. This study provide a refined chronostratigraphic framework for the internal geometry of the Shu'aiba that is used to better enhance reservoir characterization. Moreover, the Shu'aiba has been the focus as a potential exploration targets, and a recent discovery has been confirmed within the Upper Shu'aiba, where the stratigraphic trapping occurred. A detail core description was conducted and integrated with wireline logs, isotope data and biostratigraphy to define the basin architecture and depositional settings from a regional prospective. The study area extends from the onshore of the Rub Alkhali fields with its marginal to intrashelf basinal setting to the restricted platform at the east to the northern offshore fields where another intrashelf basin developed. This study accurately defined the contacts between the Biyadh (Kharaib), Hawar, Shu'aiba and Bab formation within the chronostratigraphic framework where regional paleoenvironment changed from deltaic deposits at the northeastern part to marine carbonate in the southwest. The Shu'aiba succession evolved from a flat ramp in the early TST to marginal rim at the early HST followed by late HST and prograding wedges and finally by the early LST of the intrashelf basins. The lithocodium boundstone and chalky mudstone facies form lateral extensive interval except in the basins where Lithocodium diminished. Rudist buildups locally dominated the HST and are clinoformed basinward. A link has been found between the rudist banks and structural liniments that suggest an influences of syn-depositional tectonics and topographic highs along with an environmental changes. The global sea-level fall at the end of the Aptian stage with its forced regression creating an extensive prograding wedges along the margins and toward the basins. These prograding wedges are pinching out as a toplap against the upper unconformity and were great location for the new discovery of stratigraphic traps within the Upper Shu'aiba unit in the Rub-Alkhali area. A more potential traps may occur within the other intrashelf basins in the Middle and Northern parts of the Arabian shelf.