Orange Basin Geology
The Orange Basin, offshore
Namibia and South Africa, became an oil & gas exploration hotspot in 2022
with major players like TotalEnergies and Shell. Chevron discovered the Kudu
gas field in 1974 with an estimated 1.3 TCF of gas in place, but the field is
not productive due to economics, lack of infrastructure, and rocks that may not
have adequate permeability. In 2012, Brazil’s Petrobras tried to repeat what
they had found in their pre-salt plays on the South American side in the Campos
and Santos Basins of the once connected rocks split by the mid-ocean rift
system, but were unsuccessful. Before mid-ocean rifting, the Orange Basin was
once connected as a single basin to the Pelotas Basin offshore Brazil and
Uruguay, as shown and compared below in different parameters.
The Orange Basin started as a
continental rift zone in Late Jurassic time (about 150mya), resulting in
half-grabens filling with syn-rift (deposition contemporaneous with rifting)
clastic and lacustrine sediments. Later, the basin transformed to ocean-floor
rifting with flood basalts spreading. Orange Basin reservoir rocks are mostly
Cretaceous-aged marine sandstones. Turonian source rocks are present above the
reservoirs, and Aptian source rocks are present below the reservoirs. Trapping
is typically a combination of structural and stratigraphic. The syn-rift
deposits may have deeper lacustrine source rocks within their restricted area.
Unfortunately, in January
2025, Shell wrote off about $400 million in Orange Basin projects due to higher
gas-to-oil ratios than expected and inadequate reservoir permeability in their
Graff field. The low permeability is thought to be a result of pore clogging by
clay or chlorite, or secondary calcite cementation. TotalEnergies’ nearby Venus
field also suffers from the permeability issue, and they are still evaluating
whether to develop the field and plan to decide in 2026.
BW Energy, a Norwegian firm,
is currently drilling the Kharas-1 well updip to the Kudu gas field, and
according to some geologists, possibly looking for deeper oil as well. Rasoul
Sorkhabi, in an article for AAPG Explorer, gives a synopsis of the challenges
and opportunities of the basin:
“The maximum width and depth of Orange Basin is
fashioned by the Orange river delta and further exploration is expected to
focus on this depocenter. Namibian discoveries have attracted international
attention to Orange Basin and there are still a few undrilled prospects (for
example, Ushivi in PEL 56 and Olympe in PEL 91) in Namibia. However, most of
Orange Basin is located offshore South Africa. Currently, TotalEnergies and Eco
Atlantic (Azinam) are well positioned in South African Orange Basin.”
“For 24 wells drilled in the Namibian Orange Basin since
2022, success rate of 75-percent is impressive. Nevertheless, drilling in water
depths of 2,000 meters into reservoirs 3,000 meters or deeper below the sea
floor is a costly venture and the exploration will require derisking geological
factors and suitable economic propositions.”
The Mopane 1X and 2X wells,
drilled by Galp in 2024, revealed a light oil play west of the Kudu gas field.
This discovery may have influenced BW Energy to drill updip of the Kudu gas
field, looking for better rock quality. In September 2025, Rhino Resources
finished drilling the Volans-1X, which reported commercial quantities of
rich-gas condensate at 40 ° API gravity in good reservoir quality rock. The
well is still being evaluated.
The Kudu Gas Field and the Possibility of Deeper Source
Rocks
The Kudu gas field is developed in syn-rift sediments of an inner sub-basin below the Aptian source rocks and may result from deeper Lower Cretaceous continental source rocks.
Some possible evidence for deeper source rocks is the presence of diamondoids.
The origin and occurrence of diamondoids are explained in Wikipedia:
“Diamondoids are found in mature high-temperature
petroleum fluids (volatile oils, condensates and wet gases). These fluids can
have up to a spoonful of diamondoids per US gallon (3.78 liters). A review by
Mello and Moldowan in 2005 showed that although the carbon in diamonds is not
biological in origin, the diamondoids found in petroleum are composed of carbon
from biological sources. This was determined by comparing the ratios of carbon
isotopes present.”
“In chemistry, diamondoids are g. eneralizations of the
carbon cage molecule known as adamantane (C10H16), the smallest unit cage
structure of the diamond crystal lattice.”
Diamondoids are hydrocarbons
with high thermal stability. The presence of diamondoids suggests that the Kudu
gas is sourced from cracked oil. Henk Komrick for GeoExPro gives some details
of the possible objectives of the Kharas-1 well.
“Gion Kuper, who studied the Kudu field extensively when
he worked for Tullow Oil as a petroleum systems expert, thinks that it is
plausible that the Kudu gas migrated into the currently mapped closure from
other places. “The main reason for this,” he says, “is that the current
temperature in the Kudu reservoir, although around 160 °C, is still a bit low
for the extensive level of thermal cracking suggested by the geochemical data.”
It is also thought that temperatures may not have been much higher in the past.
This makes a case for another accumulation to exist, possibly nearby, although
finding oil may be a stretch.”
“It is that slightly deeper reservoir that BW Energy
might be trying to prove now, in the hope that there is oil remaining. Finding
a deeper level of hydrocarbons would also imply that a deeper, potentially
lacustrine source rock – older than the Barremian-Aptian Kudu Shale source rock
overlying the gas reservoir – is involved in generating the bulk of the
hydrocarbons for Kudu.”
“In addition to hydrocarbon phase, reservoir quality in
the Kudu target might be one of the key risks,” adds Gion. “At these elevated
temperatures, cementation can be a significant issue, as we have also seen with
other discoveries nearby.” Saying that, if the oil was cracked in another place
on the Kudu structure, there must be something somewhere, so it is probably
worth drilling into it. Let’s see if BW Energy can make Kudu gas, and maybe
oil, work.”
According to Oil Price US: BW
Energy is moving ahead with an ambitious goal to triple its oil production to
90,000 barrels per day within three years, “driven by a mix of organic
growth, exploration success, and strategic acquisitions across Africa and South
America.” The Kharas-1 well may be targeting an updip equivalent of the
Mopane reservoir sand and possibly test for deeper oil as well. The results
could be interesting and will maybe be known soon.
References:
BW Energy Targets 90,000 BPD as Kudu Basin Drilling
Heats Up. Charles Kennedy. Oil Price US. October 8, 2025. BW
Energy Targets 90,000 BPD as Kudu Basin Drilling Heats Up
Diamondoid. Wikipedia. Diamondoid - Wikipedia
Kharas-1 well might have two surprises in store: BW
Energy is currently drilling a well in Namibian waters that aims to further
appraise the wider Kudu block, as well as a shallower target that could be
equivalent in age to Mopane. Henk Kombrink. GeoExPro. October 3, 2025. Kharas-1
well might have two surprises in store - GeoExpro
New light oil discovery draws attention away from the
Orange Basin central axis to northern promise. Peter Elliott – Nventures.
GeoExPro. February 9, 2024. New
light oil discovery draws attention away from the Orange Basin central axis to
northern promise - GeoExpro
Orange Basin of Africa: Progress, problems and
prospects. Rasoul Sorkhabi. AAPG Explorer. September 1, 2025. Orange
Basin of Africa
Chasing the Orange Basin from Namibia to Brazil. Africa
Oil+Gas Report. Geosciences. February 15, 2024. Chasing
the Orange Basin from Namibia to Brazil - Africa’s premier report on the oil,
gas and energy landscape.
Rhino announces Volans-1X probe as high liquid-yield
gas condensate discovery in excellent quality reservoir. Rhino Resources. October
1, 2025. Rhino
announces Volans-1X probe as high liquid-yield gas condensate discovery in
excellent quality reservoir - Rhino Resources
No comments:
Post a Comment