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Reducing Exploratory Risks Using Advanced Basin Modeling in a Complex Structural Setting — A Case Study From Pará-Maranhão Basin - Brazilian Equatorial Margin


The Pará-Maranhão Basin is situated in a passive margin with an orthogonal separation component related to the oblique opening of Equatorial Atlantic Margin during the Upper Albian. The exploration efforts began in the middle seventies with oil and gas discoveries from Cretaceous to Paleogene in shallow water. In the 2010´s decade, these efforts were moved from platform to deep water settings due to high resolution 3D seismic surveys that allowed the identification of potential hydrocarbon source rocks and well-developed siliciclastic channel-lobes turbidite systems. Potential reservoirs were disconnected from slope to deep water settings by a gravity driven fold and thrust belt characterized by extensional, transitional and compressional domains which developed during Paleogene age. That disruption of the system was probably due to overloading caused by the deposition of a thick cenozoic carbonate platform related to fault reactivation of the rift phase. The main exploratory risks in this context are related to migration and charge issues due to structural complexity, the role of faults in migration and sealing, the effects of overloading in source rock maturation and expulsion timing, and the overpressure resultant of the huge mass displacement. The use of a new kinematic restoration tool, KronosFlowTM, coupled with an unstructured mesh forward basin modeling tool (TemisFlowTM), allowed the best prediction of the deformation timing, the evaluation of the synchronism between trap formation and hydrocarbon charge as well as the prediction of overpressure related to deformation and overloading. Restoration results showed that the gravity driven system took place during Paleocene with the development of the listric growth fault systems in platform to near slope areas, in the extensional domain. This imbricated fault system converges at the base to a detachment surface at Upper Albian section. The evolution of this system from Eocene, with the overloading caused by sediment capture in roll-over systems triggered the rupture of the Santonian/Campanian sequences against a basement structural high and the beginning of the fold and thrust belt in the deepwater settings. The timing of deformation and trap development improves the chance of charge from late source rock levels, as Turonian and Coniacian, believed to be present and mature in deep water settings in Pará-Maranhão Basin.