South Africa: The Unpicked Fruits of the Durban and Zululand Basins

By

Varsha Singh¹

(1) Petroleum Agency SA, Cape Town, South Africa

 The South African East Coast is characterised by two distinct rift basins that developed during the Late Jurassic-Early Cretaceous break-up of the Gondwana super-continent:

(1) The Zululand Basin with its onshore extension, forms the southern extent of the Mozambique Basin. (2) The Durban Basin structurally more complex offshore, lies to the south of the Zululand Basin.

The mid-Cretaceous geology of the East Coast is dominated by sediment input from the Tugela River. With limited well control and regional seismic data, the stratigraphy has been correlated from the modern shelf into the deep-water areas of the basins. The basin geometry consists of horst and graben systems and a thick post-rift sedimentary section beyond the modern shelf edge. Seismic mapping reveals extensive systems of untested basin floor fan complexes.

The Tugela Submarine fan is extensive and prospectivity associated with the fan remains unexplored. Thermal modelling associated with the fan indicates that potential source rocks in the area have reached levels of maturity, with peak hydrocarbon generation occurring during the late Cretaceous. Background gas associated with two of the four wells drilled offshore, provides empirical evidence for a mature source basin-ward.

Reservoir quality sandstones have been documented regionally in Mozambique, and within wells and outcrops in the Zululand. Sandstone units with porosities up to 23% were penetrated in the onshore Zululand Basin.

This paper demonstrates how the above elements of a petroleum system relate to the various plays identified. Plays, which may reveal some of the juiciest fruits yet to be tasted!