Shell has made a significant oil and gas discovery at the Graff-1 well offshore Namibia. The well results have so far shown at least two reservoirs in the Upper Cretaceous, with a light oil column reported in the Santonian, in high quality channel sands. This discovery is in the deep water of the southernmost sector of the Orange Basin offshore Namibia.
Last month, Upstream Magazine reported on early positive signs from TotalEnergies’ Venus-1 wildcat in around 3,000 meters of water, also off the southern coast of Namibia, with unconfirmed reports of both oil and gas, and thick reservoirs. The well is targeting a multi-billion-barrel prospect and is in a block adjacent to the South African maritime border.
These successes in Namibia are extremely significant and encouraging for South Africa as the same geological sedimentary basin continues into South African territory, extending from the border with Namibia to offshore Cape Town, and far out to sea, comprising an area of over 160,000 square kilometers. Shell holds exploration acreage in the South African southern sector of the basin together with partners TotalEnergies and PetroSA. TotalEnergies holds further acreage in the South Africa sector of the Orange Basin with partners Sezigyn in ER343 and Impact Africa in ER335. To the east and northeast of these blocks is ER339 where Eco Atlantic will take over the Azinam holding of 20 percent, once the section 11 transfer is complete (see figure 1). There is also open acreage to the south of the TotalEnergies and Impact block, where some leads have been identified in ultra-deep water. These are based on amplitude anomalies and are interpreted as basin floor fan deposits (figure 2).
Most importantly, Graff-1 has proven the existence of a working petroleum system in the Cretaceous section of the basin with oil as a component. Previously, only gas has been discovered in the Cretaceous sector.
Orange Basin Geology
The deepwater sector of the South African Orange Basin is unexplored, but similar geology extends south of Namibia into the South African sector. Geological features similar to the Namibian reservoirs have been identified on seismic data in the South African part of the basin, also in the Cretaceous, but these remain to be tested through drilling.
New seismic data acquired by the survey planned by Searcher will assist in reducing exploration risk and help in identifying and quantifying possible oil and gas deposits off South Africa’s west coast.
The Orange Basin is a large, Mesozoic passive volcanic margin basin situated off the coasts of Namibia and South Africa. The early rift section of the basin is filled by terrestrial, lacustrine and volcanic rocks, while drift sediments comprise largely clastics deposited by the Orange, Oliphants and BergRivers, and their proto-equivalents.
To date, exploration in the South African sector has been confined to the shallow water sectors, targeting syn-rift grabens and the post-rift Cretaceous sequences. Numerous gas, condensate and even oil shows have been reported, while important discoveries include the Aptian-Albian fluvial Ibhubesi gas field and the Hauterivian synrift A-J oil discovery, both off the South African coast. The deepwater section of the basin off South Africa was first imaged on speculative data acquired by PGS in 2002, followed by multiclient surveys acquired by Spectrum in 2012, 2013 and 2014, and two large 3-D surveys. To date, the deepwater basin remains undrilled.
Besides the encouraging results from Namibia, shallower water exploration within the South African sector has delivered numerous hydrocarbon shows and discoveries, source rock intersections and amplitude-versus-offset anomalies that provide evidence of working petroleum systems and source rock sequences of Hauterivian, Barremian, Aptian and possibly Turonian age. Basin-modeling results indicate that source rocks could be mature for oil and gas generation in the deep outboard basin. A large, wide basement high lies to the west of the main synrift graben, and trends parallel to the coastline, plunging from the southeast to the northwest. This important feature forms the sole structural high in the basin and is the obvious focus for charge and migration, both from source rocks to west, as well as those within and overlying the main graben to the east.
Exploration plays in the deepwater part of the basin include the pinch-out of against the marginal ridge, Barremian clastics, basin-floor fans and turbidites in the lower to mid-Cretaceous, younger Cretaceous turbidites and fold and thrust systems resulting from gravity driven collapse of upper slope sediments. Recent work by some operators has also suggested the possible presence of carbonate platforms, deposited in the Barremian, above the Marginal Ridge.
While factors such as reservoir quality, migration, charge and trapping remain uncertain, seismic interpretation, basin modeling and evidence from drilling results in the shallow basin point to the presence of all the requirements for hydrocarbon accumulations waiting to be discovered.
Recent Seismic Activities in RSA
Two separate court cases were heard at the Grahamstown High Court of South Africa in November and December 2021. In both cases, the applicants sought an order interdicting Shell and Impact Africa Limited from proceeding with their 3-D seismic survey off the East Coast of South Africa. In the first case, brought by Border Deep Sea Angling Association and others, the application was dismissed on the basis that the applicants’ lacked supporting evidence that seismic surveys would cause irreparable harm on the marine life.
In the second case, brought by Sustaining the Wild Coast and others, an interdict was granted against Shell and Impact Africa Limited on the basis that the evidence presented showed that the consultation process was significantly flawed. Shell applied for leave to appeal, which was dismissed on the basis that a ruling on the matter would have no material effect, since Shell would only resume the seismic survey around December 2022. In terms of the court, by this date the actual matter – that is, whether the exploration right to Shell and partners was granted in compliance with regulatory requirements – would have been ruled upon.
Furthermore, in February 2022, an “interim” interdict lodged by Adams and Others was granted by the Western Cape High Court against Searcher Geodata, temporarily suspending a 2-D multiclient seismic acquisition off the West Coast of South Africa pending the hearing of an application interdicting the seismic survey.