Impact of salt-related palaeotopography on the distribution of turbidite reservoirs: Evidence from well-seismic analyses and structural restorations in the Brazilian offshore

摘要

The dynamic of gravity-driven turbidity currents is strongly influenced by the morphology of the seafloor, formed by topographic highs and lows on the margin along the depositional profile. This paper focuses on the methodology and the main results of a study on the palaeotopographic controls in a turbidite succession, with an application in an oilfield of the Brazilian offshore Campos Basin. This basin is located in the Brazilian passive margin, on which tectonics is partly controlled by halokinesis; the selected reservoirs are confined Turonian to Campanian silicidastic turbidite systems. Six seismic-lithologic horizons of regional extension were mapped, from the Aptian salt to the Miocene as well as related faults. Four main reservoir-scale units were identified, stratigraphically comprised between two of the regional horizons, and their related surfaces were mapped. The complete ensemble of horizons and faults was used to build a multi-2D geological model. Individual surface restorations performed in every horizon allowed the structural coherence and the unfolding-unfaulting quality to be evaluated. Multi-surface restorations were then carried out in order to determine the related horizon palaeotopography of each reference depositional time. The results of the geological modeling and of the structural restorations indicate that the halokinesis-related listric faults regulated the distribution of the basal reservoirs. Additionally, at the top of the Albian carbonates, a canyon was identified, which, in association with the tectonic structures form the palaeotopographic constraints for the upper reservoir geometry. This work sheds light on the importance of structural restoration in understanding the tectonic-sedimentation interactions and the palaeotopography to the distribution of the studied turbidite reservoirs.