BP’s New Oil Find in Sub-Salt Santos Basin Carbonates Offshore Brazil is Huge but There are CO2 Concerns

  

     BP describes their recent oil discovery in the Bumerangue Block Offshore Brazil, targeting carbonates in the sub-salt Santos Basin, as its biggest find in 25 years. According to BP’s press release, the well was drilled:

“…404 kilometres (218 nautical miles) from Rio de Janeiro, in a water depth of 2,372 metres. The well was drilled to a total depth of 5,855 metres.”

“The well intersected the reservoir about 500 metres below the crest of the structure and penetrated an estimated 500 metre gross hydrocarbon column in high-quality pre-salt carbonate reservoir with an areal extent of greater than 300 square kilometres.”

“Results from the rig-site analysis indicate elevated levels of carbon dioxide. bp will now begin laboratory analysis to further characterize the reservoir and fluids discovered, which will provide additional insight into the potential of the Bumerangue block. Further appraisal activities are planned to be undertaken, subject to regulatory approval.”

     This discovery also dovetails nicely with the South American emergence as the leader in oil production growth in the Western Hemisphere, which I wrote about last month.

     The abundance of CO2 in the pre-salt Santos Basin is well-established. Due to this, the CO2 is mitigated by capturing it and re-injecting it. Brazil’s Petrobras reinjected 14.2 million tons of CO2 in 2024 from 22 floating production, storage, and offloading (FPSO) vessels. It is injected for enhanced oil recovery, which makes it useful as a working fluid. Injection of produced CO2  into these pre-salt reservoirs makes up more than a quarter (28%) of the global capacity reported for 2024. Thus, the Santos Basin is a major CCS hub, or more specifically, a CCUS-EOR hub.

     A 2019 paper in Geosciences explores the geotectonic controls on the accumulation of CO2 in Brazilian pre-salt basins. Mantle intrusions associated with rifting are thought to be the source of high-CO2 areas, with small faults possibly connecting the magmatic body to the sedimentary section above it. The abstract below explains the geological hypothesis, and the maps show locations, stratigraphy, and structural features of the Santos Basin. I assume BP’s block is within or very near to the Santos Outer High, as depicted.

     Below, they explain different geological ideas about the sources and distribution of CO2 in the reservoirs.

“The large concentrations CO₂ in Santos Basin were unexpected during the early exploratory process of its deep-water areas. However, drilled pre-salt prospects have shown a wide range of CO₂ contents bringing together environmental and production complications. The mantellic origin of these CO₂ occurrences was established via noble gases isotopic analyses [4]. Nevertheless, processes and mechanisms responsible for the fate (introduction, migration, and preservation) of CO₂ in petroleum systems still remain unclear.”

“Many authors have suggested that the “CO₂-risk” in sedimentary basins could be related to the proximity of igneous intrusions and deep-seated faults, or to geothermal gradient higher than 30° C/km [3,5]. Other geoscientists suggested empirically that in some areas as, for example, in the Southeast Asia, CO₂ accumulations must be controlled by type and age of crustal basement, fault density, temperature, and pressure of reservoirs [6].”

“More recently, strong evidence has been gathered indicating that mantle helium and occurrences with higher percentages of CO₂ were related to areas of crustal thinning in depths of about 26–28 km, with thermal flux higher than 61 mW/m² [7].”

“Such conditions suggest rock melting due to the asthenosphere rising towards the crust. However, the occurrence of just one or more factors described above is not an unequivocal proxy for large accumulations of CO₂ in petroleum reservoirs. Such uncertainties are the main reason to investigate more thoroughly processes and mechanisms that generate, introduce, and accumulate CO₂ in petroleum systems. Independently of such myriad of details to be studied, a tool with the power to recognize deep related magmatic processes would be an excellent proxy to infer “CO₂-risk” in petroleum reservoirs.”

“In this way, our work focused on crustal studies is based mainly on potential method data associated with the geologic interpretation of the Jupiter Prospect data, where the highest CO₂ concentrations are reported up to date. The obtained results allow us to propose an association of the CO₂ and intracrustal intrusions of mantle-derived material.”

“Both gravity and magnetic data indicate the existence of a highly stretched continental crust under the São Paulo Plateau and a rather unique and conspicuous anomaly under the Jupiter Prospect. Modeling indicates that this anomaly corresponds to an intracrustal intrusion that reached almost to the top of the basement rocks in this area. We interpret this intrusion as the main responsible agent to transport CO₂ from the mantle into the reservoir levels in the pre-salt section of this area. Other occurrences of CO₂ in Santos Basin are all located in the stretched crust of the basin and are also interpreted as provenient from mantle material ascending along major fault segments.”

     

 

References:

 

bp announces hydrocarbon discovery at Bumerangue exploration well, offshore Brazil. BP. August 4, 2025. bp announces hydrocarbon discovery at Bumerangue exploration well, offshore Brazil | News and insights | Home

BP Announces Major Oil and Gas Discovery Off Brazil Coast. Pipeline Technology Journal. August 5, 2025. BP Announces Major Oil and Gas Discovery Off Brazil Coast | Pipeline Technology Journal

22 FPSOs in Brazil’s pre-salt enable Petrobras to break CO2 reinjection record. Melisa Cavcic. Offshore Energy. March 31, 2025. 22 FPSOs in Brazil’s pre-salt enable Petrobras to break C02 reinjection record - Offshore Energy

Geotectonic Controls on CO2 Formation and Distribution Processes in the Brazilian Pre-Salt Basins. Luiz Gamboa, André Ferraz, Rui Baptista and Eugênio V. Santos Neto. Geosciences 2019, 9(6), 252. May 14, 2019. Geotectonic Controls on CO2 Formation and Distribution Processes in the Brazilian Pre-Salt Basins