The Barremian Deep Marine Confined Channel System: Bredasdorp Basin, South Africa

Singh, Varsha¹, Jeff Aldrich¹ (1) PetroSA, Cape Town, South Africa

A number of gas and gas-condensate discoveries are present in the Bredasdorp Basin, offshore South Africa. The South Coast Gas development targets production from six gas discoveries to be tied back to existing infrastructure.

Five of the discoveries are Barremain-Aptian deep marine channel deposits. The geological model envisages sandstone deposition in a confined channel within an anastomosing system.

During the early Hauterivian, deep marine turbidite deposition was controlled by an already well-established half-graben system. A palaeovalley developed on the hanging-wall side of the northwest-southeast striking fault. The Barremian to Aptian progradational deposition of sediment accompanied the progressive widening of the Bredasdorp Basin.

A second half graben resulted from an increased rate of fault movement during the Barremian, creating a major erosional valley parallel to the fault system. At this stage the valley experienced predominantly erosion, pushing the depocentre further down-dip. An early Barremian compressional period created structural closures in a predominantly extensional regime.

During the Aptian, stacked and amalgamated channels and lobes were formed in a retrogradational setting. These sandstones are poorly imaged on the seismic data because of the low acoustic impedance contrast between the sandstones and encasing shales. In addition, the reservoirs are difficult to map due to thin sandstone beds.

This paper reviews the geological model of a single 3rd order channel system, spread over a depositional corridor of ~25km. Sixteen wells have penetrated the channel system with approximately 160 m of cores.

Channel widths and heterogeneity are documented as well as the effect of the above on the hydrocarbon trapping mechanism.