EXPLORING THE TUPI FIELD: INSIGHTS INTO STRUCTURAL CONTROLS ON DIAGENESIS IN BRAZIL'S LARGEST OIL RESERVE

The Barra Velha Formation (BVF) holds significance as a world-class oil and gas reservoir located in the Santos Basin, on the southeast margins of Brazil, South America. The Tupi field, located within the Santos Basin, is noteworthy as one of the most productive oil fields globally. The unique characteristics of the BVF, and its relative recent discovery in the early 2000s make it an intriguing oil carbonate reservoir. The BVF is understood as a continental lacustrine nonorganic carbonate sequence deposited under arid conditions.

Our seismic interpretation of Tupi Field, is concentrate on how structural controls affect fluid migration along fault systems and influence the final diagenesis within the BVF. The structural framework is significantly influenced by the Tupi High, which has led to the division of the study area into four distinct domains. The Tupi High extends in a NE-SW direction. To the west of the Tupi High, the basin deepens and the reservoir is not representative. To the east of the Tupi High, a relatively lower structural area with a distinct fault pattern is evident. The Iracema High, located in the northwest, displays a different fault direction preference compared to the rest of the Tupi Field.

Well data comparisons between the Tupi High and its adjacent structural lower reveal notable differences in depositional facies and diagenetic features. The high area is characterized by spherulite and shrub facies, with diagenesis marked by significant dissolution, dolomitization, calcite, and silica formations. In the lower structural, the most prevalent facies are mud-rich spherulites, and chemically magnesium-rich muds, with a lesser influence of silica or calcite cementation. Localized dissolution and dolomitization are also observed.

The distribution of diagenetic and primary facies can be linked to the depositional environment and the critical role played by rift faults in directing basin and hydrothermal fluids. These fluids are crucial for the formation and preservation of the diagenetic features of the BVF. Dolomite emerges as the most pervasive diagenetic phase, often associated with microcrystalline silica in later phases, filling veins and fractures. This reinforces the significance of structural control, particularly since the Tupi High is identified as the most faulted block in the region.