Table 1
Trace-metal and isoprenoid markers in crude oils
Gulf of Suez oils (Miocene)
Marker Amal 13 Amer Balaeim 19 Ramadan Shoab Aly
V/Ni 2.32 2.10 2.39 2.10 2.23
V/E Ni, Mg, FE 1.84 1.70 1.60 1.75 1.57
v/E Ni, Cu, Co 2.31 - 2.37 0.75 2.21
Pr/Ph - 0.68 0.78 0.94 0.73
Western Desert iols (Lower Creataceous)
Kahraman Salam TSW 8 WD 19 WD 33
V/Ni 0.55 0.91 1.32 1.00 1.24
V/E Ni, Mg, Ca,Co 0.08 - 0.62 0.01 0.90
V/E Ni, Cu, Co 0.44 - 1.07 0.36 1.23
Pr/Ph 3.24 3.05 1.36 1.25 1.07
M.A. Abu-Elgheit et al.
In addition to the above marker, we have utilized other markers of the type (V/E Ni, Mg, Fe) and (V/E Ni,Cu,Co) for correlations. They are also recorded in Table 1. the former has an average value of 1.69 for the Gulf of Suez oils, whereas it is only 0.40 for the Western Desrt oils. For the second marker the average values are 1.91 and 0.78 for the respective oils. These trace metal markers clearly distinguish between crude oils with respect to their geologic age. The relevance of the three markers is that they confirm the occurrence of the six metals in the crude oils during the early stages of their formation. It must be mentioned that no correlation was observed with V/Mg, V/Fe, V/Cu, V/Co, or their Ni counterparts. However, the valid correlations of the markers using composites of metal concentrations add to the significance of V and Ni whose reliable levels overshadow the partial contamination of crude oils by the other metals from different sources.
The geochemical investigation was then conducted relying upon the isoprenoid biomarker relating pristine to phytane. GC was used for performing the analysis of the saturate fractions of the deasphalted oils. A typical chromatogram of their hydrocarbons is shown in Figure 1. Similar to the trace metals, the Pr/Ph marker(Table 1) is almost uniform in the Gulf of Suez oils, revealing their same origin, yet showing marked differences in the Western Desert oils, reflecting varying compositions of source materials, conditions during hydrocarbon formation, and migrational history of the oils so formed. The change of Pr/Ph from 0.68 to 3.24 on passing from Miocene to Lower Cretaceous age is in agreement with the observation that this marker increases with oil maturity (Connan, 1973; Ten Haven et al., 1987). Its correlation with the trace-metal markers also offers the explanation that maturation is manifested by a high biological marker associated with a decrease in trace-metal content and a low trace-metal content and a low trace-metal marker.
The role of petroleum markers was also noticed in the environmental investigation. The recovered oil recovered oil spills were analyzed for their trace-metal contents, and
Retention time
Figure 1. GC of Salam crude oil saturate fraction.
Petroleum Markers for Geochemical Investigations 7