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A Multidisciplinary Study on a Representative Section From Masirah Basin-Oman


The exploration well Manarah-1 was drilled by Masirah Oil Limited in Block 50 offshore Oman in February-March 2016. A 24 meters core was cut from Manarah-1 in the Coniacian to Maastrichtian Aruma Group from the Masirah Basin, an elongated Cretaceous rift basin running parallel to the present day southeastern coast of Oman. The core recovered approximately 4 meters of reservoir quality sandstone and approximately 20 meters of a mixed siliciclastic-carbonate succession. A multidisciplinary study (petrophysics, petrography, sedimentology, geochemistry, nannopaleontology, micropaleontology and palynology) has been carried out on the core to gain a better understanding of the depositional setting, as well as age dating. The core was initially profiled using CT scanning, gamma-ray analysis, UV and white light core photography, and a detailed probe permeameter study focused on the uppermost 5 meters. Plug points were selected against these suits of data, and Routine Core Analysis was subsequently conducted. 21 thin sections were selected for petrographic study, cold-cathodoluminescence microscopy and fluid inclusion analysis were conducted on 2 and 4 samples respectively. A total of 57 samples have been analyzed for all biostratigraphic disciplines. The upper sandstone interval comprises coarse-grained sandstones deposited in distributary channels in a fluvio-deltaic setting overlying or cut into a shallow marine shelf. The latter comprises mixed carbonate-siliciclastic lithofacies becoming increasingly carbonate-dominated down hole. Nine sediment microfacies have been erected from the thin section petrography. The lower part of the cored interval appears to be Lower Campanian in age. The uppermost part of the core is essentially unfossiliferous and dominated by siliciclastics, thus confirming the fluvio-deltaic interpretation. Ages are based on an integration of all fossil groups including micropaleontology (residues and thin sections), calcareous nannofossils, and palynology (palynomorphs and dinoflagellates). Such a comprehensive data set integration provided a clear outlook of the evolutionary and depositional history of the area. The use of fine-tuned biohorizons, involving different fossil groups, allowed a robust biostratigraphic and chronostratigraphic interpretation that will be used as a reference for future drillings in the area.