Trace element geochemistry of crude oils and condensates from South African Basins

• Trace elements distribution in South African offshore basins evaluated.
• Two main oil families exist in both Bredasdorp and Orange Basins.
• The organic materials from which the oils were derived were deposited mainly under anoxic conditions.
• Both marine and terrestrial organic matter generated the oils and condensates in Bredasdorp Basin.

Crude oil and condensates samples from Bredasdorp and Orange Basins, South Africa were analyzed for trace elements using inductively coupled plasma – optical emission spectrometry. The oil and condensate samples were analyzed to classify the oils into family and to determine the origin of the oils and depositional environment of organic matter that yielded the oils using trace elements. The concentrations of the elements (Co, Cr, Cu, Fe, Mn, Ni, and V) determined ranged from 0.10 to 7364.7 ppb. Iron is the most abundant element in the samples while cobalt is least abundant. Both concentrations and ratios of nickel and vanadium showed two main families of oils; oils of marine origin and oils of terrestrial origin. Oil samples from the Orange Basin are mainly of marine source and their organic matter were deposited under anoxic conditions. Most of the oil samples from the Bredasdorp Basin are of marine origin with a few samples having terrestrial origin. Cluster analysis also classified the oil and condensate samples from the two basins into two main families of marine and terrestrial sources.