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Abstract: Geological Aspects of Petroleum Systems and Related Exploration Plays in South Africa's Orange Basin

Jungslager, Eric - SOEKOR (Pty) Ltd., South Africa

Oil and gas and active source rocks are known at several stratigraphic levels and in several areas of the Orange Basin from exploration boreholes and from geochemical "Sniffer" survey anomalies, and inferred from seismic direct hydrocarbon indicators including bottom simulating reflectors and seismic chimneys. These hydrocarbon finds and indications, their migration routes from their likely source kitchens, the reservoir-seal-trap systems hosting them, together with the location of dry boreholes allow the delineation of petroleum systems and related plays of undiscovered accumulations.

Excellent quality marine oil-prone source rocks of Aptian age have been encountered in the DSDP 361 well in the oceanic Cape Basin west of the Orange Basin. These source shales are known to extend eastward where they become mature and eventually become more gas-prone in the drilled proximal, structurally gentle areas of the Orange Basin. It is argued that an Aptian-sourced / Upper Cretaceous turbidite-reservoired oil system is at work in the undrilled distal, deeper water growth-fault and toe-thrust belts.

Gas generated by the more proximal and deeply buried correlatives of these oil-prone shales in the active gas kitchen underlying the depocenter of the Orange Basin, as well as from Barremian shales, defines an Early Cretaceous gas system within which are found the Albian discoveries off South Africa, and the Barremian Kudu gas field off Namibia.

Hauterivian source kitchens of both marine and lacustrine nature and which are known to be developed in several South West Gondwana rift and early post-rift basins and in a graben in the Orange Basin, are likely to be within the oil window in the southern part of South Africa's western margin and along a trend of grabens along the edge of the main depocenter in the north.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil