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High-frequency Forced Regressions and Their Influence on Stratigraphic Trap Generation: Examples from the Paleogene in Pelotas Basin, South Brazil

Jose Daudt
Ph.D., Exploration Geologist–South America Regional Team, BP Brazil Exploration

Abstract

The stratigraphic evolution of the Paleogene section in Pelotas Basin (South Brazil) was interpreted using 2D time data integrated with well data. High-frequency changes in the trajectory of the shelf break during the Paleogene and Eocene are interpreted to represent periods of forced regression, transgression and normal regression. These events influenced sand dispersion patterns as well as the distribution of shale-prone intervals throughout the basin, indicating the possible existence of important stratigraphic traps.

These observations, when placed within robust stratigraphic models, represent key components of the sequence stratigraphic framework, and may result in a powerful tool for reservoir and seal prediction. According to many traditional models, periods of forced regression may cause a substantial increase in sediment availability. Consequently, these events are important for delivering sediments to the deep basin, creating sand-prone submarine fans that are covered by basinal shales during the subsequent transgression. However, in this analysis, we recognize a stratigraphic signature that conflicts with these traditional models, suggesting that other processes may be affecting the studied area. An example of these apparent conflicts includes abundant evidence for forced regressive shelf edge deposits with no correspondent down dip sandy counterpart in the Eocene.

Based on this interpretation, the potential for stratigraphic traps in the deep part of the basin will be presented. Uncertainties related to the quality of potential reservoirs in relation to the timing of the shelf break migration will also be discussed.

AAPG Search and Discovery Article #90204 © AAPG Geoscience Technology Workshop, Stratigraphic Traps and Play Concepts in Deepwater Settings, May 14-15, 2014, Rio de Janeiro, Brazil