3rd-Order Depositional Sequences of the Barra Velha Formation in the Eastern Margin, Axis, and Western Margin of the Main High of the Tupi Field, Santos Basin
Event - AAPG ICE 2025
Abstract
The Tupi Field stands out as a milestone in hydrocarbon exploration and production in Brazil, characterized by its structural compartments conditioned by the movement and/or rotation of the basement during the rift phase of the Santos Basin. The main compartments identified in the seismic are the Eastern Margin, the Axis, and the Western Margin of the Main High. This study aims to compare the three 3rd-order depositional sequences of the Barra Velha Formation identified through seismic-log-rock integrated study within the three different structural compartments. The Sequence I in the Eastern Margin is bounded at its base by the Pre-Barra Velha Unconformity (PBVU), characterized by a regional unconformity that overlies the Itapema Fm. (ITA). The seismic reflectors display onlap termination against the Main High and show divergent pattern to the east. Fan delta system constitute the main sedimentary record of the Seq I. A thick autochthone carbonate mound was identified intercalated with the fan delta system suggesting a local chemical deposit occurred by ascending fluids through faults. The Seq I in the Western Margin is also bounded by PBVU that overlies the ITA. The seismic reflectors display onlap termination against the Main High and show divergent pattern to the west, consisting of fan delta system intercalated with evaporitic system. On the Axis of the Main High the Seq I is absent due to erosion or non-deposition. The PBVU directly overlies the volcanic igneous basement. The Sequence II in the Eastern Margin is composed by carbonate evaporitic system intercalated with lacustrine coastal beach system. The Seq II in the Western Margin is characterized by an abrupt facies change well defined by log analysis and core description and is composed by a thick package of argillaceous evaporitic Mg-rich silicate. The differences between eastern and western margins are interpreted as lateral variations in depositional systems controlled by paleotopography and climate in a hyperalkaline lacustrine environment. The Seq II on the Axis of the Main High overlies directly on the volcanic rocks and is characterized by coarse grained clastic fan delta system. The Sequence III in the Eastern Margin exhibits homogeneous thickness, parallel-planar seismic reflectors pattern, and is composed by lacustrine coastal beach system, suggesting that reworking in this margin was effective due to high-energy wave action. The Seq III in the Western Margin and in the Axis shows homogeneous thickness, parallel-planar seismic reflectors pattern, and is composed of evaporitic system. This study shows that the sequences I and II present onlap terminations and divergent seismic reflectors pattern in the eastern and western structural compartments indicating a strong structural control due to the uplifted of the Main High, whereas the Seq III exhibits homogeneous thickness and parallel-planar seismic reflectors indicating attenuation of this tectono-structural control over time. The differences of depositional systems among the three structural compartments can be explained by the distinct structural-geomorphological configuration in the field scale. The record of the three 3rd-order depositional sequences highlights the tectono-structural control on stacking patterns and depositional systems in Tupi Field. The accurate mapping of these three sequences provides a robust predictive geological model enhancing reservoir characterization and optimizing hydrocarbon recovery.
