Preliminary interpretation of a vast swath of three dimensional(3D) seismic data in Namibia’s hydrocarbon rich Orange Basin, has provided clues for a contiguous relationship between the Orange basin and the Pelota basin in Southern Brazil and Uruguay.
“The time for a conjugate leap from the significant discoveries of Namibia’s Orange Basin to the unexplored Pelotas Basin of Southern Brazil and Uruguay is upon us”, write Neil Hodgson, Lauren Found and Karyna Rodriguez, all geoscientists at Searcher, the Australian geophysical company.
In the last two years, the Orange Basin, which is present in both Namibia and South Africa, has yielded discoveries of hundreds of millions of barrels of crude oil and gas after exploratory drilling in its Nambian segment by Shell and TOTAL Energies.
From late 2022 to June 2023, Searcher completed acquisition of 6,700square kilometres of three dimensional (3D) seismic data in two phases, representing the largest multi-client 3D offering in the entire Basin, in Petroleum Exploration Licences PEL 85 and PEL 3 respectively.
“The Aptian source rock of Namibia can be correlated to its twin in the Pelotas Basin of Southern Brazil and Uruguay”, Hodgson et al assert, in an article published in Geo Expro, a Norway based earth science journal.
“The Aptian source rock is clearly identifiable in the seismic of the Orange Basin in Namibia as a soft topped unit with lower internal frequency, little internal structure, standing out in AVO space as a classic strong type IV anomaly”, the authors collectively note.
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column; a subdivision of the Early or Lower Cretaceous Epoch or Series. It encompasses the time from 121.4 ± 1.0 million years ago (Ma) to 113.0 ± 1.0 Ma, approximately.
The authors argue that Aptian source has proved so effective in Namibia with TotalEnergies’ Venus-1 discovery and Shell’s four up-slope discoveries, all charged from the Aptian source rock, potentially offering tens of billions of barrels of recoverable light oil. Hodgson and his co-authors talk of using a geophysical tool, the amplitude versus offset (AVO) or amplitude variation with offset, in an innovative way, to tease out how the source rock of Aptian age in Namibia’s Orange Basin correlates with the Aptian source rock in the Pelotas basin.
“AVO has historically been used as a tool to look for oil or gas in clastic reservoirs i.e., a Direct Hydrocarbon Indicator (DHI) tool”, the scientists declare.
“Yet in our process (and multiple other examples since the technique was promoted by Løseth et. al. in 2011), we turn this on its head and use AVO to characterise and identify source rock”. It is no surprise at all, they contend, “that this source rock can also be identified from its seismic character in the Pelotas Basin of Brazil and Uruguay where it presents the same as Orange Basin but thicker and has a similar Type IV AVO response. The only surprise is that the Aptian sourced plays in this basin remain untested on this margin”.
The three scientists say that “Like human un-conjoined twins though, the Pelotas Basin’s lifestyle choices have varied somewhat from its Orange Basin twin. The continual dynamic topography induced instability of the Namibia margin and a lower sediment supply via the Orange River has led to a comparatively thin sedimentary section than is observed in Pelotas, whose sedimentary section is, however, demonstrably stable, where no dynamic topographic inversion and shelf collapse has occurred and sediment supply via the proto-Platte River has been prodigious, generating a rather more generously proportioned sedimentary deposit than its West African twin”.
Therefore, only at the edges of the Pelotas Delta is the Aptian source rock buried just deep enough to generate Oil. In such places, the Aptian is prodigious and is no-doubt charging some of the worlds’ biggest prospects in the Cretaceous counter regional play.
“It is here that Searcher is acquiring 3D seismic in 2023/4 season”.
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