The Orange Basin: Challenges for Future Exploration
Varsha Singh1, David van der Spuy2, and O. M. Kandjoze3
1New Ventures: Upstream, PetroSA, Cape Town, South Africa
2Promotions, Petroleum Agency SA, Cape Town, South Africa
3Exploration and Production, NAMCOR, Windhoek, Namibia
Offshore exploration in the Orange Basin is still at a very early stage with no wells drilled in water depths greater than 1000m. All exploration drilling has focussed on the shelf where there are proven hydrocarbon resources.
The Orange Basin which straddles the South African - Namibian border, is part of the South Atlantic passive margin and was formed during the rifting of the South American and African plates. The underlying structure of the Orange basin consists of synrift half - grabens trending sub parallel to the coastline. Post - rift features of the basin include growth faults and toe thrusts within the distal part of the drift succession. A thick wedge of Cretaceous to tertiary sediments built out over an Early Cretaceous rift section, and formed a major basin system extending approximately 160 000 km2 to the 2000m isobath.
The most well documented petroleum system is the natural gas system generated from the lower Aptian and Barremian shales. The occurrence of an active petroleum system has been documented by the Kudu field (Barremian source) to the north and Ibhubesi field (Aptian source) to the south as well as numerous discoveries and shows. A number of addition petroleum play types have been identified by exploration companies either from direct evidence i.e. drilling or by analogy. Several speculative petroleum systems and plays are also prognosed in the undrilled parts of the basin. Potential sandstone reservoirs are expected in the Lower Cretaceous and have been intersected by exploration wells. To the South these fluvial-deltaic sands have excellent reservoir properties with porosities and permeabilities of more than 22% and 400 mD respectively.
While the potential resource base is vast, the exploration challenge is now focused on understanding the regional economic viability of the potential petroleum systems defined in the Orange Basin.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery