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Open AccessArticle

Geochemical Evaluation of the Cretaceous Mudrocks and Sandstones (Wackes) in the Southern Bredasdorp Basin, Offshore South Africa: Implications for Hydrocarbon Potential

1
Department of Geology, University of Fort Hare, Private Bag X1314, Alice 5700, Eastern Cape Province, South Africa
2
DSI-NRF CIMERA, Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, Johannesburg 2006, South Africa
3
Department of Geology and Mining, University of Limpopo, Private Bag X1106, Sovenga 0727, Limpopo Province, South Africa
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(7), 595; https://doi.org/10.3390/min10070595
Received: 15 May 2020 / Revised: 24 June 2020 / Accepted: 26 June 2020 / Published: 30 June 2020
The southern Bredasdorp Basin, off the south coast of South Africa, is only partly understood in terms of its hydrocarbon potential when compared to the central and northern parts of the basin. Hydrocarbon potential assessments in this part of the basin have been limited, perhaps because the few drilled exploration wells were unproductive for hydrocarbons, yielding trivial oil and gas. The partial integration of data in the southern Bredasdorp Basin provides another reason for the unsuccessful oil and gas exploration. In this study, selected Cretaceous mudrocks and sandstones (wacke) from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1 and E-D3 drilled in the southern part of the Bredasdorp Basin were examined to assess their total organic carbon (TOC), thermal maturity, organic matter type and hydrocarbon generation potential. The organic geochemical results show that these rocks have TOC contents ranging from 0.14 to 7.03 wt.%. The hydrogen index (HI), oxygen index (OI), and hydrocarbon index (S2/S3) values vary between 24–263 mg HC/g TOC, 4–78 mg CO2/g TOC, and 0.01–18 mgHC/mgCO2 TOC, respectively, indicating predominantly Type III and IV kerogen with a minor amount of mixed Type II/III kerogen. The mean vitrinite reflectance values vary from 0.60–1.20%, indicating that the samples are in the oil-generation window. The Tmax and PI values are consistent with the mean vitrinite reflectance values, indicating that the Bredasdorp source rocks have entered the oil window and are considered as effective source rocks in the Bredasdorp Basin. The hydrocarbon genetic potential (SP), normalized oil content (NOC) and production index (PI) values all indicate poor to fair hydrocarbon generative potential. Based on the geochemical data, it can be inferred that most of the mudrocks and sandstones (wackes) in the southern part of the Bredasdorp Basin have attained sufficient burial depth and thermal maturity for oil and gas generation potential. View Full-Text
Keywords: Bredasdorp basin; geochemical parameters; kerogen type; thermal maturity; hydrocarbon potential Bredasdorp basin; geochemical parameters; kerogen type; thermal maturity; hydrocarbon potential
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Baiyegunhi, T.L.; Liu, K.; Gwavava, O.; Wagner, N.; Baiyegunhi, C. Geochemical Evaluation of the Cretaceous Mudrocks and Sandstones (Wackes) in the Southern Bredasdorp Basin, Offshore South Africa: Implications for Hydrocarbon Potential. Minerals 2020, 10, 595.

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