Written by guest contributor William (Bill) Heines, Chief Geoscientist at Getech.
Today’s headlines of mammoth oil discoveries in the post-rift Upper Cretaceous of deepwater Namibia are just the latest dispatch from a long and winding exploration journey along both sides of the South Atlantic.
The chase after post-rift Upper Cretaceous clastic plays in the Atlantic margins began in the late 20th century with giant shallow water Upper Cretaceous discoveries in Brazil in the 1970s and 1980s. Exploration success in the post-rift Upper Cretaceous clastic play continued with the Ceiba and Okume discoveries in 1999 and 2001 in the Rio Muni Basin offshore Equatorial Guinea. The same exploration team later went on to discover the Jubilee field offshore Ghana in 2007, which is widely considered the catalyst for Upper Cretaceous turbidite exploration in the deepwater of the Atlantic margins. The industry pushed the boundaries further in 2011, with the Barra discovery in the Sergipe Alagoas Basin proving a commercial post-rift Cretaceous play on oceanic crust.
The pre-salt Lower Cretaceous carbonate play took longer to breakthrough in the deepwater. The first hints of encouragement came with pre-salt oil shows at Baleia in 1996 in the Kwanza Basin, and Jubarte in 2002. That interest was transformed by the giant Tupi discovery in the Santos Basin in 2006, which opened one of the world’s most important pre-salt oil provinces and again stimulated the industry to explore for the play in Africa. The concept crossed the Atlantic with the Cameia discovery offshore Angola in 2012, however, success in the deepwater offshore Africa pales into insignificance compared to South America.
Exploration has been bouncing East and West and North and South ever since.
Depositional Environment & Paleo-Slope Angle: Sierra Leone – Liberia Example. Margin steepness impacts commercial success. Source: Westwood South Atlantic Margin Study 2026
Each new experience, especially commercial success but also technical successes and failures, spurred a new wave of investigation elsewhere as explorers tried to replicate the old recipes in a new kitchen or test evolving concepts. Source rocks from the Barremian to the Turonian, carbonate and sandstone reservoirs, steep margins and shallow, different kinds of underlying crust, different tectonic settings/structural styles, and different palaeowater depths/distance from the palaeo-shoreline all lent colours to the exploration palette.
Now Getech and Westwood have teamed up to draw the balance on nearly two decades of well results that clearly illuminate the unfolding picture with the South Atlantic Margin Study. Not surprisingly, one of the strongest insights is that geology matters.
At the most obvious level, the opening of the South Atlantic was diachronous from North to South and asymmetrical from East to West, meaning that the precise timing and style of the key factors is unique in every basin. Conditions vary from basin to basin, and even within each basin, imparting important nuance that can only be deconvolved by evaluating each basin in its own context, and can only be compared meaningfully within the broader evolutionary history of region. The study summarises the geological history of the South Atlantic to keep the exploration history in context. This comprehensive catalogue of 425 wells and their results provide the first database capable of finessing out the relative contribution of each important element to success or failure.
For example, it is evident on inspection that the biggest number of successful wells, with billions of barrels of resource, is found on the rifted continental fragment of the Santos Basin, whereas there has been no commercial success on strike-slip crust on either side of the ocean; this compilation now allows testing the exact success rate (both technical and commercial) associated with every crustal type along all segments of both margins, and teasing out the related influence of kinematic style. Even within the Santos Basin there is attenuated continental crust and transitional magma-poor crust, each with its own distinctive suite of environmental conditions and corresponding rates of technical and commercial success that are different from the headline-grabbing parts of the basin. Across the whole region, technical success rate is approximately equal between magma-poor and magma-rich transitional crust, but the commercial success rate between the two is different by almost a factor of two. Only with the detailed well results can we begin to deconvolve the disparity in rate of commerciality and size of resource additions.
Steepness of the margin and depositional environments influence the degree to which sediments may pond on or bypass the slope. In general, ponding of sediments within intra-slope mini-basins is associated with a distinctly different technical and commercial success rate for stratigraphic traps than non-ponded slopes, and steeper slopes with a different success rate from flatter ones.
Every basin has multiple source rocks at different stratigraphic positions and with different geographic distribution, but it is evident that not every spot in every basin has access to a source. Details of source rock maturation and timing, as well as reservoir quality, will depend on the details of burial and thermal history that vary according to rift timing and geometry, crustal type, and sediment loading history. Important economic issues like relative abundance of oil vs gas and potentially fatal permeability impairment start to make sense when viewed in a full geological history context across the region.
Of course, the picture varies from basin to basin, with local nuance from the interaction of other critical factors affecting technical and commercial success rates. Only by considering the ensemble of all factors, which are documented for every well, can we get a firm impression of the local reasons for success and failure, and begin to formulate rigorous expectations for success in underexplored parts of the South Atlantic, such as the Pelotas and Punta del Este basins on the South American side of the Austral segment. Even though the experience base in those basins is sparse (to say the least, with only one well), the rest of the geologic context of the basins is known and can be compared to other basins and other segments of the region to formulate rational hypotheses and predictions.
In the South Atlantic Margin Study Westwood has characterised 425 wells drilled between 2007 and 2025 in 23 basins that span both sides of the South Atlantic from the Marathon Fault Zone in the North to the Agulhas-Falkland Fault Zone in the South. The characterisation covers present-day water depth, the age and lithology of targeted reservoirs, as well as the kind and volume of hydrocarbons proven, and any technical and/or commercial success (or failure). Westwood has placed each well in geologic context using Getech’s Globe knowledgebase, covering key factors influencing exploration performance like crustal domain, source rock, kinematic style, depositional slope type, angle of palaeo-slope, and distance to palaeo-shoreline.
This study provides for the first time an integrated, uniformly documented information store that can guide evidence-based exploration planning and focus detailed geologic studies on the aspects of each palaeo-tectonic and palaeo-environmental setting that truly matter for success or failure.
Guest Author
William A. Heins, Chief Geoscientist – Getech
William A. Heins, PhD, PG, is Chief Geoscientist at Getech. A sedimentary geologist with more than three decades of experience, Bill specialises in basin analysis, sedimentology, reservoir quality prediction and regional geoscience across petroleum and emerging subsurface energy applications including natural hydrogen and geothermal. Before joining Getech, he spent more than 14 years at ExxonMobil Upstream Research, where he helped develop the patented SandGEM reservoir prediction system. Bill holds a PhD in Geology from UCLA and degrees in Geology and Economics from the University of Pennsylvania.
Bill will also be speaking at Westwood’s Offshore Energy Houston: State of the Market 2026 event taking place on Tuesday 27th October 2026. Find out more here.
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