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

Evaluating rare earth elements as a proxy for oil–source correlation. A case study from Aer Sag, Erlian Basin, northern China

“…Since the concentrations of trace elements in crude oils can be influenced by in-reservoir alteration processes such as thermal degradation and biodegradation as well as migration (Al-Shahristani and Al-Atyia, 1972;Tissot and Welte, 1984;Barwise, 1990;Greibrokk et al, 1994;López et al, 1995), there may be difficulty using absolute concentrations in correlation studies. However, trace element ratios (e.g., V/Ni and Ni/Co) of crude oils are often constant and have been used widely in correlation studies (Hirner, 1987;Akinlua et al, 2007Akinlua et al, , 2015Shi et al, 2015). In this study, the V/(V + Ni) ratios in extracts of mudstones and oil sands varied widely, ranging from 0.04 to 0.65 (Table 5).…”

“…Prior studies (Hirner, 1987;Akinlua et al, 2007Akinlua et al, , 2015 indicated that biologically important elements such as V, Ni and Co can be used as reliable parameters for oil-oil and oil-source correlations. Since the concentrations of trace elements in crude oils can be influenced by in-reservoir alteration processes such as thermal degradation and biodegradation as well as migration (Al-Shahristani and Al-Atyia, 1972;Tissot and Welte, 1984;Barwise, 1990;Greibrokk et al, 1994;López et al, 1995), there may be difficulty using absolute concentrations in correlation studies.…”

“…Generally, the highest concentrations of metal elements are found in crude oils which are immature (Barwise, 1990;Oluwole et al, 1993;Akinlua et al, 2015) and/or biodegraded crude oils (Hodgson and Baker, 1959;Udo et al, 1992;López et al, 1995;Akinlua et al, 2007). Many studies (Zaki et al, 1989;Frankenberger, 1994;Duyck et al, 2002;Selby et al, 2007) also indicate that trace elements in crude oils are mainly found in the asphaltene fractions and to a minor extent in the resin fractions.…”

“…On the one hand, the concentrations of V and Ni in crude oils are controlled by organic matter types and depositional environments of source rocks (Lewan and Maynard, 1982;Lewan, 1984;Barwise, 1990). On the other hand, their concentrations can also be influenced by in-reservoir alteration processes (thermal degradation, biodegradation) and petroleum migration (Al-Shahristani and Al-Atyia, 1972; López et al, 1995;Akinlua et al, 2015).…”

“…Although these alterations might change the concentration of trace elements in crude oils, some elemental ratios remain constant in many instances, such as the V/Ni ratio (Al-Shahristani and Al-Atyia, 1972;Lewan, 1984;Tissot and Welte, 1984;López et al, 1995). Numerous studies (Hodgson and Baker, 1959;Al-Shahristani and Al-Atyia, 1972;Lewan and Maynard, 1982;Lewan, 1984;Hitchon and Filby, 1984;Ellrich et al, 1985;Hirner, 1987;Curiale, 1987;Barwise, 1990;Oluwole et al, 1993;Filby, 1994;Frankenberger, 1994;López et al, 1995López et al, , 1998Akinlua et al, 2007Akinlua et al, , 2015Finlay et al, 2012) have indicated that the concentration and distribution of trace elements in crude oils provide not only vital information for the origin and maturation of petroleum as well as depositional environment of its source rocks, but also a potential tool for oil-oil and/or oil-source correlation. For a long time, due to discovery of organometallic carriers (porphyrin complexes) and relatively high abundance of V and Ni in crude oil (Lewan and Maynard, 1982;Tissot and Welte, 1984;Barwise, 1990;Filby, 1994), V and Ni in crude oil have received more attention than other trace elements and have been used widely in petroleum exploration.…”