--> Characterization of Permian Mangrullo Formation (Uruguay) Oil Shale as a Source Rock and Its Correlation With Irati (Brazil) and Whitehill (South Africa) Formations
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Characterization of Permian Mangrullo Formation (Uruguay) Oil Shale as a Source Rock and Its Correlation With Irati (Brazil) and Whitehill (South Previous HitAfricaNext Hit) Formations

Abstract

During the Early Permian (Artinskian), a large inland sea developed across southern Previous HitAfricaNext Hit and southern South America. These restricted conditions allowed the accumulation of organic matter and the deposition of oil shales. Mangrullo Formation, as defined in Uruguay, is a lithostratigraphic unit of Parana Basin constituted by oil shales, mudstones and carbonates developed in this depositional setting. The formation crops out in northeast Uruguay, reaching up to 35 meters in thickness. Regionally, the unit can be correlated with Irati Formation in southern Brazil and Whitehill Formation in South Previous HitAfricaNext Hit and southern Namibia. In Brazil, subject to certain local conditions, the Irati shales have matured and generated. Heavy oil occurrences can be observed in the Permian sandstones of Pirambóia Formation, stratigraphically above Irati. However, the available outcrop and well data shows that Irati and Mangrullo shales are generally immature, mostly reaching the oil window through local heating by Early Cretaceous dykes and sills. This resource has been developed in southern Brazil since the 70s, involving its mining and the production of oil and gas through pyrolysis, on an industrial scale. An assessment made in the 80s at the Uruguayan side, estimated that 277 million barrels of oil can be obtained by pyrolysis of Mangrullo shales within a few areas studied. Despite the large research regarding pyrolysis of Irati and Mangrullo, there is not such knowledge of other potential uses for these resources, in particular the production of energy through combustion processes. There is also an opportunity to properly characterize Mangrullo oil shale to assess its source rock potential. The objective and contribution of this work is to characterize their source rock properties, by analysing core samples of a stratigraphic well located northeast of Uruguay, and compare the results with Irati and Whitehill shales. Overall, the results indicate that Mangrullo can be termed as excellent quality oil and gas prone source rock, with high TOC% values and mostly type II kerogen. In the location of the well, the shales are just entering the oil window at a present day depth of 20 metres, having generated a small amount of free hydrocarbons. It is expected that in the central and northwest region of the Parana Basin in Uruguay, where they are preserved at greater depth as recent well data suggests, these oil shales may reach enough maturity to generate significant volumes of oil.