Successful Infrastructure-Led Exploration Case: Atlanta Oilfield Ring Fence, BS-4 Concession, Post-Salt Play, Santos Basin

Abstract The case of Atlanta-NE oil accumulation is a successful application of the infrastructure-led exploration (ILX) strategy in the offshore Brazilian Santos Basin, where many smaller opportunities in the post-salt play were left behind after the discovery of the giant pre-salt play oilfields. Those results from the Atlanta oil field ring fence show how these exploration opportunities may become economically attractive by considering the existing field facilities for their development. Atlanta is a post-salt (Eocene) heavy oilfield (14°API), located in the northern portion of the deepwater Santos Basin. Oil in place volumes are close to 1,2 Bbbl. Oil production started in 2018, by using an Early Production System (EPS), while the first oil from the Field's Definitive System (DS) started at 31/12/2024. After the DS implementation, smaller exploratory opportunities in the post-salt play within the Atlanta ring fence may become economically attractive during the field development. Atlanta-NE oil accumulation is the most important exploration upside mapped within the ring fence. Indeed, it is a shallow pool drilled in 2006 by 9-SHELL-19D well, located over the NE corner of the Atlanta oilfield. The reassessment of that opportunity was made in 2023, when additional geological data were collected through a pilot well (9-ATL-8DP-RJS well) drilled during the Atlanta development well drilling campaign. The Atlanta NE pilot well allowed the acquisition of proper log data, fluid samples and pressure measurements (MDT) in that shallower reservoir, confirm the excellent reservoir quality, heavy oil occurrence and its commercial potential, to be developed through the Atlanta oilfield DS. The Atlanta-NE reservoirs are composed of turbidite sandstones partially eroded by several massive transport complexes (MTC) during the Late Eocene. Those reservoirs were mapped using 3D seismic depth data (PSDM) acquired in 2012 and reprocessed in 2019. Later, seismic attributes such as spectral decomposition and acoustic impedance volumes contributed to a better definition of the oil pool. Petrophysical parameters were provided by 9-SHEL-19D and 9-ATL-8DP-RJS well datasets. After the interpretation of the new available geological and geophysical datasets, it was possible to define both the Atlanta-NE oil accumulation area (11km²) and the reservoir's depositional area (53km2). The upgrade of the Atlanta-NE discovery into a commercial oilfield resulted from the application of the ILX strategy concepts in the Atlanta oilfield ring fence. The same approach may be applied to additional exploration opportunities within the post-salt play in the Santos Basin and other Brazilian offshore basins as well.