Geological Modelling of the Offshore Orange Basin, West Coast of South Africa

Curnell Campher
Petroleum Agency SA, Cape Town, South Africa

The Orange Basin covers an area of roughly 130 000 square kilometers relevant to the 200 m isobath (Gerrard & Smith, 1982) and has roughly one well drilled for every 4000 square kilometers. The basin has proven hydrocarbon reserves and potential for further discoveries.

The study area is located within South African exploration license blocks 3A/4A and 3B/4B and covers a region of roughly 97 km by 150 km. The study aims at understanding the geological processes responsible for the formation of the Orange Basin with a focus on the evolution of source rocks maturity. The Petrel software was used for seismic interpretation and well correlation and PetroMod (IES, Version 10) for basin modelling and assessing source rock maturity.

Preliminary seismic interpretation of the post Hauterivian succession shows a relative thickening of the sedimentary sequence westward as the basin evolves from the early drift to complete drift phase. Initial results from petroleum system modelling indicate that the Barremian- early Aptian source rock is at present over mature and producing mostly gas in the shelf areas whereas potential for oil is most likely still present in the deep water area of the basin where Tertiary progradation has resulted in renewed petroleum generation. The younger Cenomanian-Turonian source rock shows a lower transformation ratio than the older source rocks and modelling indicates that the source rock is mainly producing oil. Additional modelling is needed to further constrain the model results.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery