--> Determination of rupture structures, and location of possible oil seepage in the Peniche Basin, Portugal

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Determination of rupture structures, and location of possible oil seepage in the Peniche Basin, Portugal


The Peniche Basin is one of the basins in the West Iberian Margin, located west of the Berlengas horst, in the Portuguese deep offshore. As this basin has not been drilled its sedimentary infill is still unknown. However, since the Peniche Basin occupies a parallel position to the Lusitanian Basin it is considered that similarities are likely in their filling, geodynamics and petroleum systems. The main purpose of the present work is to know the geographic position of the rupture points of the different petroleum systems. Therefore, for the present study we considered three different petroleum systems: (i) The Paleozoic Petroleum System, whose source rock is located in the basement, (ii) The Lower Jurassic Petroleum System, whose source rock dates from the Plienbachian and (iii) The Upper Jurassic Petroleum System whose source rock dates from the Oxfordian. Seismic stratigraphic interpretation indicates that the Peniche Basin has endured a tectonic inversion episode from Upper Cretaceous up until today, allowing the fracturing of key elements of the petroleum systems. In this paper a set of structures is identified that may correspond to migration paths along which hydrocarbons may move up to the surface, in the Peniche Basin. For this study twenty six 2D seismic reflection profiles were observed, courtesy from PETROBRAS, in order to individualize the structures that may lead to the formation of oil seeps. The purpose of this work is to identify the geographic location of these structures on seismic profiles so a vulnerable area could be delimited. For this study, it was assumed that any fault or fracture that reaches the surface could lead to the hydrocarbon leakage, considering that a petroleum system is compromised by faulting. Therefore the places where oil leakage may occur were identified. Considering the extension of the faults and the units intercepted it was also possible to determine the petroleum system more likely to be involved. Based on the geographic distribution of these structures, two distinct areas were delimited, separated by the Nazaré Canyon: (i) one, less deformed, in the north, (ii) another, southerly, with more evidences of deformation. The region with higher deformation implies the existence of a higher number of faults and fractures, representing locally the sector in the Peniche Basin where hydrocarbon seepage is more likely to occur.