Evidence of Petroleum System Evolution of the Southern Bredasdorp Basin, South Africa: A Multi-Dimensional Approach
Lihle Madyibi1, Rolando di Primio2, George Smith1, Gesa Kuhlmann2, and Zahie Anka2
1Geological Sciences, University of Cape Town, Cape Town, South Africa
2Department 4 Chemistry of the Earth, GeoForschungsZentrum, Potsdam, Germany
The southernmost Bredasdorp Basin, offshore South Africa, remains only partially understood with respect to petroleum systems evolution when compared to the northern and central flanks of the basin. The southern flank of the basin has been unsuccessful for hydrocarbons with most of the wells drilled to date yielding insignificant oil and gas shows. Incomplete integration of data in the southern area is a possible reason for the oil and gas search being hitherto unsuccessful. In this study, we apply a two-dimensional, later up-scaled to a three-dimensional, modeling approach in order to advance our understanding of the petroleum systems evolution in the southern flank of the Bredasdorp Basin.
The model is based on the interpretation of 64490m two-dimensional seismic-reflection profiles, as well as the analyses of well logs and cores that constrain the sedimentary facies distribution and the units’ age. Four main source rock intervals (Barremian, Aptian and Turonian) were modeled for maturity and hydrocarbon generation.
Different scenarios of erosion and heat flow histories were considered for model calibration. The best calibration with vitrinite reflectance data is achieved when an erosive event, removing up to ~ 800 m of Maastrichtian to early Paleogene sediments, is accounted for in the model. Maturity predictions suggest that the Barremian and Aptian source rocks are currently mature and started generating hydrocarbons at about 80 Ma, whereas the Turonian source rock is immature. Present-day modeled transformation ratios for both mature source rocks are higher than 50%. Nevertheless, petroleum generation seems to be halted at about 69 to 35 Ma and 12 to 0 Ma due to minimal burial depth of sediments.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery