--> Direct Oil and Gas Evidences from Punta Del Este Basin, Offshore Uruguay: New Data From Fluid Inclusions

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Direct Oil and Gas Evidences from Punta Del Este Basin, Offshore Uruguay: New Data From Fluid Inclusions

Abstract

The Uruguayan offshore basins are considered frontier areas for hydrocarbon exploration. A growing database of 2D seismic and, recently, near 40,000 square km of 3D seismic, has greatly improved the prospectivity of the basins. Although the only two wells drilled so far (Gaviotín and Lobo wells - Chevron, 1976) were declared dry and did not find source rock beds, it should be noted that both were located on structural highs in the proximal sector of the Punta del Este Basin and are not representative of the ~8 km thick fill of the basin. In 1996, results from a study by AMOCO showed the presence of light (32 API), paraffinic oil inclusions as well as gas inclusions in Cretaceous sandstones of both wells. Recently, a detailed study using new technologies was performed by FIT (Fluid Inclusion Technologies) on more than 1,000 cutting samples from the Gaviotín and Lobo wells. These new data indicate dominantly dry gas response in certain intervals, along with some wet-gas-range hydrocarbon species. Low, moderate and/or high gravity oil inclusions were found in 28 thin sections of sandstones and volcanic materials with fluorescence colors including yellow, yellow-white and blue-white. Additionally, common live (fluorescent) stain was noted. High oil inclusion abundance in certain horizons is indicative of possible paleo-oil accumulations, which were displaced. The study suggests that migration took place in the Late Oligocene-Early Miocene. Removal of at least 2,000–2,800 ft of sediments is required to explain possible biodegradation of shallower accumulations. Efficiency of the regional seal (deposited in the Maastrichtian-Paleocene transgression) is evident from the available data. Overall, these results demonstrate the generation of native hydrocarbons, migration pathways and the existence of paleo-hydrocarbon accumulations. Probable source rocks for these hydrocarbons include lacustrine shales of Late Jurassic-Neocomian age and marine shales of Aptian, Turonian and Paleocene age. Acknowledgements. We are indebted to Dr. Don Hall (FIT).