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Proven and Potential Clastic Reservoir Intervals within the Stratigraphic Framework of the Orange Basin, Offshore South Africa

Davids, Anthea C.
Promotion Division, Petroleum Agency SA, Bellville, South Africa.

The geology off South Africa's west coast margin evolved in response to the fragmentation of Gondwana. It comprises a wide passive margin basin related to the opening of the South Atlantic in the late Jurassic to Early Cretaceous. This basin is known as the Orange Basin and is the largest South African offshore basin. A variety of play types, including both stratigraphic and structural trapping opportunities, have been identified.

The aim of this study is to discuss the three proven as well as potential reservoir intervals in the basin, comprising the:

  • Valanginian-Hauterivian fluvio-deltaic and lacustrine sandstone packages intersected within the graben in the rift sequence.
  • Barremian age shoreline and shallow marine sandstone reservoirs were intersected in the transitional to early drift section.
  • Late Aptian to Late Cenomanian fluvial reservoir unit of the drift section.
  • The potential reservoir units not intersected to date in the Orange Basin include the pre-Hauterivian, the Hauterivian-Aptian and possible Tertiary deepwater sands. The following can be observed of such potential reservoirs:
    • The pre-Hauterivian is of unknown reservoir quality and it is possible that the earliest synrift as well as basement have potential as fractured reservoir.
    • Porosity reduction due to great burial depths poses a major element of risk for Hauterivian-Aptian leads.
    • Deepwater fans dominate the Tertiary beyond the shelf edge, but effective sealing poses a risk.

The Orange Basin is largely underexplored with only one well per 4000 km2 and has potential for the successful accumulation of hydrocarbons, possibly in significant quantities. Nonetheless, a number of uncertainties remain which results in a high level of geological risk. Further 2D and 3D seismic acquisition as well as drilling programs may be of great benefit in mitigating these risks.


AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012