--> Petroleum Systems Analysis of the Gamtoos Basin, South Africa
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2018 AAPG International Conference and Exhibition

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Petroleum Systems Analysis of the Gamtoos Basin, South Africa

Abstract

The Gamtoos Basin, offshore the southern coast of South Africa was formed as a consequence of the breakup of the African and South American plate during the late Jurassic. (Broad et.al, 2006). The oldest dated sediments encountered in the basin are of Kimmeridgian age and constitute a significant source rock. The basin is relatively under explored with only 10 shallow wells drilled in an area of approximately 4000 square kilometeres. These wells are mainly focused around the main Gamtoos graben area. The current study aims to assess the maturity of three source rock units namely the Kimmeridgian, Tithonian and Valanginian/Hauterivian source rocks, intersected in a few wells in the Gamtoos Basin, on a regional scale. The study comprised the construction of Previous Hit1-DNext Hit models of 6 drilled wells and 29 pseudo wells spread over the area of the basin. The maturity of all three source rock intervals in the Previous Hit1-DTop models was integrated and assessed at various periods throughout geological time to trace the evolution of source rock maturity up to the present day. Results of the modelling show that the older Kimmeridgian source rocks are over mature in the basin depocentre but still hold potential for oil generation away from the depocentre where they are less deeply buried. The Tithonian and Valanginian/Hauterivian source rocks show a similar trend with the more mature sections of the source rock in the main graben area, where there is a substantial sedimentary package. The study proved that the source rock is indeed more mature in the main Gamtoos graben and also highlights areas where the source rocks could be in the oil window.