Thermotectonic history of the Maastrichtian reservoir in Campos Basin

The present study of the Carapebus Formation on well samples refines our understanding of the thermotectonic history of the Maastrichtian oil reservoir in Campos Basin. Our investigations are based on the thermal analysis of 55 cuttings samples, of which 45 have also been analyzed with apatite fission track (AFT) dating, in addition to eleven cores analyzed for vitrinite reflectance (VR) and spore color. The apatites are partially annealed and the AFT central ages does not provide precise information on exhumation and thermotectonic events that occurred in the source terrain, whereas the youngest AFT ages provide a minimum age of 45.9 ± 5.5 Ma due to significant track annealing in the rocks. The VR (0.37-0.48 %Ro), spore color and Thermal Alteration Index (TAI) data correspond to the immature zone of hydrocarbons. The thermal history integrated with seismic profiles demonstrate that two phases of heating happened to reservoir, separated by a cooling event (65-37 Ma). The first heating phase started after deposition of the Carapebus Formation until 65 Ma and the second during late Eocene and reflect the subsidence at the basin. The cooling event shows a strong correlation with subaerial unconformity related in the basin and an important thermal uplift coeval with the last volcanic pulses of the Trindade mantle plume in the basin. During the uplift phase, the generation of hydrocarbon in reservoir was ceased and no more generation occurred until the Recent.