First EAGE Conference on South Atlantic Offshore Energy Resources

Migrated hydrocarbons originated from deep source of thermogenic petroleum, can serve as a source of carbon and energy for microorganisms in deep subseafloor. Key microbes metabolizing those hydrocarbons could be the starting point for the development of novel prospection tools for the exploration in offshore basins. During the scientific campaign named YTEC-GTGM 4, sediment samples were collected by gravity coring in the north of the offshore Argentina Basin. Total DNA was extracted from samples, followed by amplification and sequencing of the 16S rRNA gene. Data processing allowed to identify bacteria sequences previously reported in the literature linked to the breakdown of gaseous alkanes and/or whose presence were also noted in hydrocarbon migration zones. These taxa supported the thermogenic origin of occluded/adsorbed gases confirmed by the geochemical characterization of the sediments. In addition, the prediction of the functional potential of bacteria communities demonstrated much-undiscovered diversity. These results encourage us to explore complementary metagenome sequencing technologies to examine the taxonomic and functional diversity of the sediment microbiome, to confirm the role of these bacteria.

Recent significant light oil discoveries (Venus-1X, Graff-1X and Jonker-1X) have driven interest in the prospectivity of the Orange Basin and the entire Namibia-South Africa margin. These exploration wells have de-risked key issues of source maturity and trap charge of the outboard plays. Light hydrocarbons were encountered within both Upper and Lower Cretaceous clastics, proving reservoir presence and trapping mechanisms of multiple stratigraphic plays in the deepwater. Although the recent discoveries have proven reservoir quality and presence in the outboard plays, evaluating the development and variations in reservoir provenance is crucial to correlate the newly de-risked deepwater plays with the untested fairways along the margin.

Academic studies discussing the source-to-sink evolution for the Namibia-South Africa margin show the potential for significant sediment volumes to be present in the outboard as a result of periodic margin uplift and denudation. On regional 2D seismic, we see evidence for sizeable outboard deposits in the Aptian-Albian and Upper Cretaceous. The majority of the deepwater area has not yet been tested but we can infer that the deepwater has the greatest chance of finding reservoir quality sands in comparison to the relatively muddy near-shore areas due to slope-bypass and long-distance sediment transport mechanisms along this margin.

This study uses minimal prior information to place into context the exploration potential for two prospects that lack well information in the Pelotas and Punta del Este Basins using analogue benchmarking of individual prospects in the two primary plays.

These plays have been identified by prior work as the most likely to be successful and have prompted the only offshore drilling in recent years ( Rodriguez et al., 2019 ). The intent of this study is to place previous work that describes the hydrocarbon potential of offshore Uruguay in the context of similar prospects and plays worldwide.

Objective analogue analysis serves as quality assurance on the accuracy of technical predictions, including highlighting potential gaps, issues, and biases. This work summarizes findings from ongoing research to quantify predictions and outcomes on a parameter, volume, and uncertainty basis.

The workflow can be used in a variety of low-data situations to increase confidence in interpretation and decrease risk by narrowing uncertainty. This study demonstrates that methodical and critical application of analogues can quantitatively augment available data with information based on historical performance, instead of relying on subjective and qualitative individual and team experience of ostensibly similar analogues.

In the Austral segment of the South Atlantic, the conjugate margins of Southern Brazil/Uruguay/Argentina and Namibia/South Africa have comparable geomorphological elements. Recent play-opening light oil discoveries (Venus, Graff and Jonker) in deep-water Namibia have increased exploration interest in the whole Austral South Atlantic margin, de-risking outboard stratigraphic plays and providing analogues for conjugate margin exploration.

With attention being given to the Southern Atlantic due to its analogy to the prolific African Coast, improved seismic images are crucial to well understand the region and its prospects. In this paper, we present the results of a re-processing using vintage narrow azimuth towed streamer (NATS) data over Uruguay’s coast including both pre-processing and velocity model building using the latest processing technologies, such as Time Lag Full Waveform Inversion. This allows us to achieve improvements when compared to the legacy image, updating the potential from this type of datasets, and bringing new insights in upcoming exploration areas.

Structural framework that controls the aptian sedimentation in the distal-central region of Uruguay’s offshore basins is identified and mapped in this work. In addition, its relevance from a petroleum perspective is studied. The Aptian sequence is a world-class source rock that generated 29% of the world’s hydrocarbon reserves, as well as the recent discoveries in Cretaceous reservoirs in Namibia’s Orange Basin. As a result, determining the presence and characteristics of the aptian sequence has become critical for any assessment of the petroleum potential in the passive-margin basins of the South Atlantic. Several paleo-restorations show that the Orange Basin and Uruguay offshore basins are conjugated margins generated during the Atlantic breakup (Upper Jurassic-Lower Cretaceous). Additional analogies have been developed throughout these basins, resulting in regional aptian sequence deposition on both margins. Although multiple researchers recognize the seismic facies of the Aptian sequence on Uruguay’s offshore basins, their characteristics are likely different from those deposited in the Orange Basin. This is due to the specific structural controls that allowed the development of a depocenter during Barremian-Aptian times, which contributed to marine restrictions and larger thicknesses of Aptian, both of which have important implications for the generation and accumulation of hydrocarbons offshore Uruguay.

This study focuses on the recent sedimentary deposits in the Colorado basin, which comprise a vast contourite depositional system (CDS) along the continental slope. The formation of this CDS is attributed to the northward flow of modern deep-water masses, resulting in both erosive and depositional features. As part of the "Pampa Azul Initiative," a national program promoting ocean science research in Argentina, a bathymetric dataset covering an area of 13,000 km2 was acquired during the YTEC-GTGM 4 cruise in 2019 aboard the R/V Austral. Additionally, six sediment cores were extracted during the same survey. In this study, we analyze the bathymetric and sediment data alongside multichannel 2D seismics to characterize the contourites on the lower slope that shape the present-day seafloor. Furthermore, we examine the underlying fault system. By investigating the geological processes driving the formation of the CDS and studying subsurface structural features, we aim to gain insights into the dynamics of the Northern Argentine Continental Margin and identify potential seepage systems in the region.

Offshore Exploration at the Golfo San Jorge basin is in an early/middle stage, even after 60 years since the first geophysical acquisitions and 30 drilled wells in an area of more than 55,000 km2 and still with non-commercial discoveries. The deep objectives have a high remaining potential, considering the results of the onshore deposits, where they continue to optimize the projects to the classic reservoirs of the basin. For this reason, it is of interest to keep geological models and workflows updated for the characterization of critical elements of petroleum systems.

Understanding the geological evolution of the Pelotas and Punta del Este basins is crucial for a more comprehensive insight into the South American passive margin. Nevertheless, despite their significant geological value, these basins have hitherto been lacking in geochemical studies. Addressing this knowledge gap, we carried out new whole-rock geochemistry and, for the first time in these basins, zircon U-Pb provenance studies. Our geochemical analysis offered a robust evaluation of the overall provenance and maturity of the sediments that fed the basins, while the new detrital zircon studies allowed for precise identification of the source areas. The detrital zircon points to multiple sources, with main provenance related to grains accretioned during the Brazilian-Pan-African tectonic cycle and significative changes from the Cretaceous to nowadays. Additionally, the detrital zircon analyses offered an enhanced understanding of the basin basement and the influence of littoral drift and bottom currents on the sedimentation of the Punta del Este and Pelotas basins. In conclusion, this investigation demonstrated the importance of geochemical and provenance studies for a better understanding of the geological history and hydrocarbon potential of the Pelotas and Punta del Este basins.