Estudo tectono-sedimentar da bacia de Pelotas

Abstract

The Pelotas Basin is the southernmost basin on the Brazilian margin, resulting from the Gondwana breakup. The basin covers an area of 250,000 km², limited to the north by the Alto Florianópolis (Santa Catarina, Brazil) and to the south by the Alto Polonio (Uruguay). Its thickness reaches up to 12 km from the Barremian to the Recent. It is a unique basin in the South Atlantic when compared to other basins of the same margin due to the presence of a very thick package of sewarddipping reflectors and the lack of known hydrocarbon reserves. However, it is still considered hydrocarbons depleted compared to other basins on the margin. Since it is a basin with genetic specificities (structural and stratigraphic), different from other Brazilian marginal basins, it was necessary to generate new data and analyze and reinterpret existing data. The present doctoral thesis is committed to the stratigraphic aspects and comprises studies on the basin filling and structural compartmentalization. The data base includes seismic and wells from the Brazilian National Agency for Petroleum, Natural Gas and Biofuels (ANP). This data was analyzed in the Petrel software versions 2017, 2018, 2020, developed by Schlumberger, and TemisFlow Petroleum System Software version 2019, developed by the French Petroleum Institute and BeicipFranlab – Oil and Gas Consultancy. The studies consisted of seismic interpretation, backstripping, South Atlantic spreading rate analysis, and 2D numerical basin modeling. The results allowed to identify the Andean Cordillera tectonic influence on the Pelotas Basin sedimentation as uplift pulses and identify the climatic influence of the Drake Passage widening from the Oligo-Miocene through the contour currents record. The interaction between the South American, Antarctic, and Nazca tectonic plates was identified as the root of these influences. Additionally, overpressure in the Rio Grande Submarine Fan was well constrained for the first time by numerical modeling, and its causes were identified, including high sedimentation rate, a thick package of subcompacted shales, and smectite-illite transformation.