Тип бассейна:
Подтип бассейна:
Класс бассейна:
Возраст бассейна:
Тип полезных ископаемых:
Геологический возраст начало:
Геологический возраст конец:
Площадь: 127366.73 км²
Outeniqua Basin
The Outeniqua Basin is situated off the south coast of South Africa and it comprises four inboard shallow water sub-basins in water depth less than 200 m (the Bredasdorp, Pletmos, Gamtoos and Algoa sub-basins), and the deep water extension of those, the Southern Outeniqua sub-basin. The Outeniqua basin is bounded to the south by the northeast-southwest trending Agulhas-Falkland Fracture Zone (AFFZ) which formed during the southern South Atlantic break-up. Over the past ~160 Ma the Outeniqua Basin has undergone extension, transformation and subsidence; such that the improved continuity and resolution gained from newly reprocessed 2D seismic data is requisite to observe the development of structural architecture, sedimentation and basin morphology through time.
Continental rifting and margin extension that preceded the opening of the southern South Atlantic Ocean started in the Late Jurassic and rift architecture is followed the structural grain inherited from the underlying Ordovician-Devonian Cape Super Group of the Gondwana Orogeny (~300 Ma). Evidences of the role of a pre-existing fabric during basin formation have been observed on the reprocessed seismic data, such as the pronounced erosion of highly deformed pre-rift Cape Super Group, and low angle listric faulting of a half-graben developed and detached on an imbricate thrusting structure. During the Valanginian, right lateral shear developed along the AFFZ, accommodating the break-up of the southern South Atlantic. This right lateral strike-slip deformation continued until the Middle Aptian effecting basin architecture and geometry. Localised transpressional and transtensional deformation (such as complex pull-up and flower structures) is observed in the Southern Outeniqua sub-basin, representing a strike-slip style of deformation.
PETROLEUM SYSTEM
The Outeniqua Basin is the conjugate margin to the Falkland Plateau on the South American plate. Giant oil discoveries in the North Falklands Basin by Rockhopper such as Sea lion and Isobel Elaine, each containing a billion barrels of recoverable oil reserves, share the same Barremian source rock as the oil discoveries made in the shallow water Bredasdorp sub-basin. There have been several hydrocarbon discoveries in the shallow water of the Outeniqua Basin since 1969, beginning with a gas and condensate discovery in well Ga-A1 in the Pletmos sub-basin with 85 MMboe recoverable reserves. This was followed by a number of discoveries during the 1980s and 1990s including the largest oil and gas discoveries to date, Sable (50 MMboe) and Mossel Bay Complex (357 MMboe) respectively in the Bredasdorp sub-basin.
There are three proven source rock intervals encountered within the basin; a syn-rift Late Jurassic lacustrine shale, a Hauterivian-Barremain restricted marine mudstone and an Early Aptian anoxic restricted marine mudstone. These source rock intervals are correlated across the basin using seismic-well tied markers, revealing the morphology of the basin through time.
Several undrilled prospects have been identified within this reprocessed dataset, classifying in following play concepts.
· Fractured and sub-aerial quartzite (Table Mountain Formation of Cape Super Group) pre-rift play (Figure 1).
Figure 1. Undrilled basement highs identified on reprocessed 2D seismic profiles in the Pletmos (Figure b) and Southern Outeniqua (Figure a) sub-basins. The line location is indicated in Figure (c). Pre-rift Cape Fold Belt interpretation is based on gravity and seismic data. Hot colours on Bouguer gravity anomaly of 150 km resolution indicate basement high areas.
· Large syn-rift structures such as rotated fault blocks, roll-over anticlines and draped sands over structural highs (Figure 2).
Figure 2. Undrilled high amplitude reflectors within the syn-rift rotated fault blocks, draped sands above the rotated fault blocks, and large basin floor fans.
· Large basin floor fan and channel plays with bright amplitude reflectors supported by positive Amplitude Versus Angle (AVA) attribute anomalies (Figure 2 and 3).
Figure 3. Large basin floor fans displaying flat spots. The seismic lines are located in the Southern Outeniqua sub-basin. The high amplitude reflectors are associated with positive AVA attribute anomalies on both strike and dip lines.
Attribute anomalies derived from the reprocessed seismic data indicate the presence of direct hydrocarbon indicators (DHI’s). Examples of up to 15 km long Late Cretaceous flat spots (interpreted as fluid-water contacts) are identified within bright amplitude reflectors of basin floor fan geometry (Figure 3). These high amplitude reflectors are also supported by AVA attribute anomalies on both strike and dip lines (Figure 3) and are interpreted to indicate the presence of gas. Resource estimates for these plays are significant and the improved imaging of the reprocessed seismic allows for significant risk reduction and supports future exploration for giant discoveries, unleashing the potential of this underexplored southern corner of Africa.
Data source:Future giant discovery in the Outeniqua Basin, offshore South Africa. Anongporn Intawong, Neil Hodgson, Anthea Davids, Chantell van Bloemenstein, Curnell Campher. 2017
Следующий Бассейн: Rio Muni